Publications

Scholarly Journals--Published

  • Jullienne A, Quan R, Szu JI, Trinh MV, Behringer EJ, Obenaus A. Progressive vascular abnormalities in the aging 3xTg-AD mouse model of Alzheimer’s disease. Biomedicines. 10(8): 1967, 2022. PMID: 36009514; PMCID: PMC9405684; doi: 10.3390/biomedicines10081967 Vascular dysfunction and structural abnormalities in Alzheimer's disease (AD) are known to contribute to the progression of the pathology, and studies have tended to ignore the role of the vasculature in AD progression. We utilized the 3xTg-AD mouse model of AD to examine individual cerebral vessels and the cortical vascular network across the lifespan. Our vessel painting approach was used to label the entire cortical vasculature, followed by epifluorescence microscopy. The middle cerebral artery (MCA) tree was assessed with confocal microscopy, and a new method was developed to assess branching patterns as a measure of aging-related changes. We found that vascular remodeling was profoundly altered at 4-6 months of age, when the 3xTg-AD mouse is known to transition to cognitive impairment and Aβ deposition in both sexes. Analysis of vascular features (density, junctions, length) of the MCA territory highlighted sex-dependent differences across the 3xTg-AD mouse lifespan, with no alterations in branching patterns. Our current cerebrovascular angioarchitectural analyses demonstrate progressive alterations in individual cortical vessels, as well as in the vascular network of the cortex. These new findings advance our understanding of brain anatomy and physiology in the 3xTg-AD mouse, while potentially identifying unique diagnostic signatures of AD progression. (08/2022) (link)
  • Hakim MA, Pires PW, Behringer EJ. Isolation and functional resolution of arteriolar endothelium of mouse brain parenchyma. J Vis Exp. e63463, 2022. PMID: 35343953; PMCID: PMC9154351; doi: 10.3791/63463; jove.com/t/63463 Cerebral blood flow is conveyed by vascular resistance arteries and downstream parenchymal arterioles. Steady-state vascular resistance to blood flow increases with decreasing diameter from arteries to arterioles that ultimately feed into capillaries. Due to their smaller size and location in the parenchyma, arterioles have been relatively understudied and with less reproducibility in findings than surface pial arteries. Regardless, arteriolar endothelial cell structure and function—integral to the physiology and etiology of chronic degenerative diseases—requires extensive investigation. In particular, emerging evidence demonstrates that compromised endothelial function precedes and exacerbates cognitive impairment and dementia.   In the parenchymal microcirculation, endothelial K+ channel function is the most robust stimulus to finely control the spread of vasodilation to promote increases in blood flow to areas of neuronal activity. This paper illustrates a refined method for freshly isolating intact and electrically coupled endothelial “tubes” (diameter, ~25 μm) from mouse brain parenchymal arterioles. Arteriolar endothelial tubes are secured during physiological conditions (37 °C, pH 7.4) to resolve experimental variables that encompass K+ channel function and their regulation, including intracellular Ca2+ dynamics, changes in membrane potential, and membrane lipid regulation. A distinct technical advantage versus arterial endothelium is the enhanced morphological resolution of cell and organelle (e.g., mitochondria) dimensions, which expands the usefulness of this technique. Healthy cerebral perfusion throughout life entails robust endothelial function in parenchymal arterioles, directly linking blood flow to the fueling of neuronal and glial activity throughout precise anatomical regions of the brain. Thus, it is expected that this method will significantly advance the general knowledge of vascular physiology and neuroscience concerning the healthy and diseased brain. (03/2022) (link)
  • Chum PP, Hakim MA, Behringer EJ. Cerebrovascular microRNA expression profile during early development of Alzheimer’s disease in a mouse model. J Alzheimer’s Dis., 85(1): 91-113, 2022. PMID: 34776451; doi: 10.3233/JAD-215223  Abstract. Background: Emerging evidence demonstrates association of Alzheimer’s disease (AD) with impaired delivery of blood oxygen and nutrients to and throughout the brain. The cerebral circulation plays multiple roles underscoring optimal brain perfusion and cognition entailing moment-to-moment blood flow control, vascular permeability, and angiogenesis. With currently no effective treatment to prevent or delay the progression of AD, cerebrovascular microRNA (miRNA) markers corresponding to post-transcriptional regulation may distinguish phases of AD. Objective: We tested the hypothesis that cerebrovascular miRNA expression profiles indicate developmental stages of AD pathology. Methods: Total RNA was isolated from total brain vessel segments of male and female 3xTg-AD mice [young, 1–2 mo; cognitive impairment (CI), 4–5 mo; extracellular amyloid- plaques (A), 6–8 mo; plaques+neurofibrillary tangles (AT), 12–15 mo]. NanoString technology nCounter miRNA Expression panel for mouse was used to screen for 599 miRNAs. Results: Significant (p < 0.05) downregulation of various miRNAs indicated transitions from young to CI (e.g., let-7g & miR-1944, males; miR-133a & miR-2140, females) and CI to A (e.g., miR-99a, males) but not from A to AT. In addition, altered expression of select miRNAs from overall Pre-AD (young + CI) versus AD (A + AT) were detected in both males (let-7d, let-7i, miR-23a, miR-34b-3p, miR-99a, miR-126-3p, miR-132, miR-150, miR-151-5p, miR-181a) and females (miR-150, miR-539). Altogether, at least 20 cerebrovascular miRNAs effectively delineate AD versus Pre-AD pathology. Conclusion: Using the 3xTg-AD mouse model, these data demonstrate that cerebrovascular miRNAs pertaining to endothelial function, vascular permeability, angiogenesis, inflammation, and A/tau metabolism can track early development of AD. (01/2022) (link)
  • Hakim MA & Behringer EJ. Methyl-beta-cyclodextrin restores KIR channel function in brain endothelium of female Alzheimer’s disease mice. J Alzheimer’s Dis Rep., 5(1): 693-703, 2021. PMID: 34755043; PMCID: PMC8543374; doi: 10.3233/ADR-210016   Abstract. Background: As the sixth-leading cause of death in the United States, Alzheimer’s disease (AD) entails deteriorating endothelial control of blood flow throughout the brain. In particular, reduced inward-rectifying K+ (KIR) channel function in animal models of aging and AD compromises endothelial function and optimal perfusion of brain parenchyma. Deficient endothelial KIR channels may result from aberrant interaction with plasma membrane cholesterol as a primary regulator of membrane fluidity and ion channels. Objective: We tested the hypothesis that mild methyl--cyclodextrin (MCD) treatment to reduce membrane cholesterol may restore endothelial KIR channel function in brain endothelium of old AD mice. Methods: Membrane potential was continuously measured in isolated endothelial tubes from posterior cerebral arteries of young (1 to 3 months) and old (16 to 19 months) female 3xTg-AD mice before and after mild treatment with the cholesterolremoving agent MCD (1 mmol/L). Elevated extracellular potassium ([K+]E; 15 mmol/L) and NS309 (1 mol/L) activated KIR and Ca2+-activated K+ (SKCa/IKCa) channels respectively before and after MCD treatment. Results: SKCa/IKCa channel function for producing hyperpolarization remained stable regardless of age group and MCD treatment (Vm: ∼–33 mV). However, as deficient during AD, KIR channel function was restored (Vm: –9 ± 1 mV) versus pre-MCD conditions (–5 ± 1 mV); a progressive effect that reached –14 ± 1 mV hyperpolarization at 60 min following MCD washout. Conclusion: In female animals, MCD treatment of brain endothelium selectively restores KIR versus SKCa/IKCa channel function during AD. Thus, the endothelial cholesterol-KIR channel interface is a novel target for ameliorating perfusion of the AD brain. (09/2021) (link)
  • Hakim MA, Nye-Chum P, Buchholz JN, Behringer EJ. Aging alters cerebrovascular endothelial GPCR and K+ channel function: Divergent role of biological sex. J Gerontol A Biol Sci Med Sci., 75(11):2064-2073, 2020. PMID: 31760422; doi: 10.1093/gerona/glz275 Abstract Age-related dementia entails impaired blood flow to and throughout the brain due, in part, to reduced endothelial nitric oxide signaling. However, it is unknown whether sex affects cerebrovascular Gq-protein-coupled receptors (GPCRs) and K+ channels underlying endothelium-derived hyperpolarization (EDH) during progressive aging. Thus, we simultaneously evaluated intracellular Ca2+ ([Ca2+]i) and membrane potential (Vm) of intact endothelial tubes freshly isolated from posterior cerebral arteries of young (4-6 mo), middle-aged (12-16 mo), and old (24-28 mo) male and female C57BL/6 mice. Purinergic receptor function (vs. muscarinic) was dominant and enhanced for [Ca2+]i increases in old females versus old males. However, Ca2+-sensitive K+ channel function as defined by NS309-evoked Vm hyperpolarization was mildly impaired in females versus males during old age. This sex-based contrast in declined function of GPCRs and K+ channels to produce EDH may support a greater ability for physiological endothelial GPCR function to maintain optimal cerebral blood flow in females versus males during old age. As reflective of the pattern of cerebral blood flow decline in human subjects, inward-rectifying K+ (KIR) channel function decreased with progressive age regardless of sex. Combined age-related analyses masked male versus female aging and, contrary to expectation, hydrogen peroxide played a minimal role. Altogether, we conclude a sex-based divergence in cerebrovascular endothelial GPCR and K+ channel function while highlighting a previously unidentified form of age-related endothelial dysfunction as reduced KIR channel function. (10/2020) (link)
  • Hakim MA and Behringer EJ. Development of Alzheimer's disease progressively alters sex-dependent KCa and sex-independent KIR channel function in cerebrovascular endothelium. J Alzheimer’s Dis., 2020. PMID: 32651315; doi: 10.3233/JAD-200085    Background: Development of Alzheimer's disease (AD) pathology is associated with impaired blood flow delivery of oxygen and nutrients throughout the brain. Cerebrovascular endothelium regulates vasoreactivity of blood vessel networks for optimal cerebral blood flow. Objective: We tested the hypothesis that cerebrovascular endothelial Gq-protein-coupled receptor (GPCR; purinergic and muscarinic) and K+ channel [Ca2+-activated (KCa2.3/SK3 and KCa3.1/IK1) and inward-rectifying (KIR2.x)] function declines during progressive AD pathology. Methods: We applied simultaneous measurements of intracellular Ca2+ ([Ca2+]i) and membrane potential (Vm) in freshly isolated endothelium from posterior cerebral arteries of 3×Tg-AD mice [young, no pathology (1- 2 mo), cognitive impairment (CI; 4- 5 mo), extracellular Aβ plaques (Aβ; 6- 8 mo), and Aβ plaques + neurofibrillary tangles (AβT; 12- 15 mo)]. Results: The coupling of ΔVm-to-Δ[Ca2+]i during AβT pathology was lowest for both sexes but, overall, ATP-induced purinergic receptor function was stable throughout AD pathology. SKCa/IKCa channel function itself was enhanced by ∼20% during AD (Aβ+ AβT) versus pre-AD (Young + CI) in males while steady in females. Accordingly, hyperpolarization-induced [Ca2+]i increases following SKCa/IKCa channel activation and Δ[Ca2+]i-to-ΔVm coupling was enhanced by ≥two-fold during AD pathology in males but not females. Further, KIR channel function decreased by ∼50% during AD conditions versus young regardless of sex. Finally, other than a ∼40% increase in females versus males during Aβ pathology, [Ca2+]i responses to the mitochondrial uncoupler FCCP were similar among AD versus pre-AD conditions. Conclusion: Altogether, AD pathology represents a condition of altered KCa and KIR channel function in cerebrovascular endothelium in a sex-dependent and sex-independent manner respectively. (07/2020) (link)
  • Stoll S, Xi J, Ma B, Leimena C, Behringer EJ, Qin G, Qiu H. The valosin-containing protein protects the heart against pathological Ca2+ overload by modulating Ca2+ uptake proteins. Toxicol Sci. pii: kfz164, 2019. PMID: 31368507; doi: 10.1093/toxsci/kfz164 Stress-induced mitochondrial calcium (Ca2+) overload is a key cellular toxic effectors and a trigger of cardiomyocyte death during cardiac ischemic injury through the opening of mitochondrial permeability transition pore (mPTP). We previously found that the valosin-containing protein (VCP), an ATPase-associated protein, protects cardiomyocytes against stress-induced death and also inhibits mPTP opening in vitro. However, the underlying molecular mechanisms are not fully understood. Here, we tested our hypothesis that VCP acts as a novel regulator of mitochondrial Ca2+ uptake proteins and resists cardiac mitochondrial Ca2+ overload by modulating mitochondrial Ca2+ homeostasis. By using a cardiac-specific transgenic (TG) mouse model in which VCP is overexpressed by 3.5 folds in the heart compared to the wild type (WT) mouse, we found that, under the pathological extra-mitochondrial Ca2+ overload, Ca2+ entry into cardiac mitochondria was reduced in VCP TG mice compared to their little-matched WT mice, subsequently preventing mPTP opening and ATP depletion under the Ca2+ challenge. Mechanistically, overexpression of VCP in the heart resulted in post-translational protein degradation of the mitochondrial Ca2+ uptake protein 1 (MICU1), an activator of the mitochondria Ca2+ uniporter (MCU) that is responsible for mitochondrial calcium uptake. Together, our results reveal a new regulatory role of VCP in cardiac mitochondrial Ca2+ homeostasis and unlock the potential mechanism by which VCP confers its cardioprotection. (07/2019) (link)
  • Behringer EJ and Hakim MA. Functional interaction among KCa and TRP channels for cardiovascular physiology: modern perspectives on aging and chronic disease. Int J Mol Sci. 20(6): pii: E1380, 2019. PMID: 30893836; PMCID: PMC6471369; doi: 10.3390/ijms20061380 Effective delivery of oxygen and essential nutrients to vital organs and tissues throughout the body requires adequate blood flow supplied through resistance vessels. The intimate relationship between intracellular calcium ([Ca2+]i) and regulation of membrane potential (Vm) is indispensable for maintaining blood flow regulation. In particular, Ca2+-activated K? (KCa) channels were ascertained as transducers of elevated [Ca2+]i signals into hyperpolarization of Vm as a pathway for decreasing vascular resistance, thereby enhancing blood flow. Recent evidence also supports the reverse role for KCa channels, in which they facilitate Ca2+ influx into the cell interior through open non-selective cation (e.g., transient receptor potential; TRP) channels in accord with robust electrical (hyperpolarization) and concentration (~20,000-fold) transmembrane gradients for Ca2+. Such an arrangement supports a feed-forward activation of Vm hyperpolarization while potentially boosting production of nitric oxide. Furthermore, in vascular types expressing TRP channels but deficient in functional KCa channels (e.g., collecting lymphatic endothelium), there are profound alterations such as downstream depolarizing ionic fluxes and the absence of dynamic hyperpolarizing events. Altogether, this review is a refined set of evidence-based perspectives focused on the role of the endothelial KCa and TRP channels throughout multiple experimental animal models and vascular types. We discuss the diverse interactions among KCa and TRP channels to integrate Ca2+, oxidative, and electrical signaling in the context of cardiovascular physiology and pathology. Building from a foundation of cellular biophysical data throughout a wide and diverse compilation of significant discoveries, a translational narrative is provided for readers toward the treatment and prevention of chronic, age-related cardiovascular disease. (03/2019) (link)
  • Hakim MA and Behringer EJ. Simultaneous measurements of intracellular calcium and membrane potential in freshly isolated and intact mouse cerebral endothelium. J Vis Exp. 143: e58832, 2019. PMID: 30735188; PMCID: PMC6506161; doi: 10.3791/58832; https://www.jove.com/video/58832 Cerebral arteries and their respective microcirculation deliver oxygen and nutrients to the brain via blood flow regulation. Endothelial cells line the lumen of blood vessels and command changes in vascular diameter as needed to meet the metabolic demand of neurons. Primary endothelial-dependent signaling pathways of hyperpolarization of membrane potential (Vm) and nitric oxide typically operate in parallel to mediate vasodilation and thereby increase blood flow. Although integral to coordinating vasodilation over several millimeters of vascular length, components of endothelium-derived hyperpolarization (EDH) have been historically difficult to measure. These components of EDH entail intracellular Ca2+ [Ca2+]i increases and subsequent activation of small- and intermediate conductance Ca2+-activated K+ (SKCa/IKCa) channels. Here, we present a simplified illustration of the isolation of fresh endothelium from mouse cerebral arteries; simultaneous measurements of endothelial [Ca2+]i and Vm using Fura-2 photometry and intracellular sharp electrodes, respectively; and a continuous superfusion of salt solutions and pharmacological agents under physiological conditions (pH 7.4, 37 °C). Posterior cerebral arteries from the Circle of Willis are removed free of the posterior communicating and the basilar arteries. Enzymatic digestion of cleaned posterior cerebral arterial segments and subsequent trituration facilitates removal of adventitia, perivascular nerves, and smooth muscle cells. Resulting posterior cerebral arterial endothelial "tubes" are then secured under a microscope and examined using a camera, photomultiplier tube, and one to two electrometers while under continuous superfusion. Collectively, this method can simultaneously measure changes in endothelial [Ca2+]i and Vm in discrete cellular locations, in addition to the spreading of EDH through gap junctions up to millimeter distances along the intact endothelium. This method is expected to yield a high-throughput analysis of the cerebral endothelial functions underlying mechanisms of blood flow regulation in the normal and diseased brain. (01/2019) (link)
  • Hakim MA, Buchholz JN, Behringer EJ* (2018). Electrical dynamics of isolated cerebral and skeletal muscle endothelial tubes: differential roles of G-Protein coupled receptors and K+ channels. Pharmacol Res Perspect. 6(2), e00391.*Corresponding author. Electrical dynamics of freshly isolated cerebral endothelium have not been determined independently of perivascular nerves and smooth muscle. We tested the hypothesis that endothelium of cerebral and skeletal muscle arteries differentially utilizes purinergic and muscarinic signaling pathways to activate endothelium-derived hyperpolarization. Changes in membrane potential (Vm) were recorded in intact endothelial tubes freshly isolated from posterior cerebral and superior epigastric arteries of male and female C57BL/6 mice (age: 3-8 months). Vm was measured in response to activation of purinergic (P2Y) and muscarinic (M3) receptors in addition to small- and intermediate-conductance Ca2+-activated K+ (SKCa/IKCa) and inward rectifying K+ (KIR) channels using ATP (100 μmol·L-1), acetylcholine (ACh; 10 μmol·L-1), NS309 (0.01-10 μmol·L-1), and 15 mmol·L-1 KCl, respectively. Intercellular coupling was demonstrated via transfer of propidium iodide dye and electrical current (±0.5-3 nA) through gap junctions. With similarities observed across gender, peak hyperpolarization to ATP and ACh in skeletal muscle endothelial tubes was ~twofold and ~sevenfold higher, respectively, vs cerebral endothelial tubes, whereas responses to NS309 were similar (from resting Vm ~-30 mV to maximum ~-80 mV). Hyperpolarization (~8 mV) occurred during 15 mmol·L-1 KCl treatment in cerebral but not skeletal muscle endothelial tubes. Despite weaker hyperpolarization during endothelial GPCR stimulation in cerebral vs skeletal muscle endothelium, the capability for robust SKCa/IKCa activity is preserved across brain and skeletal muscle. As vascular reactivity decreases with aging and cardiovascular disease, endothelial K+ channel activity may be calibrated to restore blood flow to respective organs regardless of gender. (04/2018)
  • Kapela A, Behringer EJ, Segal SS, Tsoukias NM (2018). Biophysical properties of microvascular endothelium: Requirements for initiating and conducting electrical signals. Microcirculation. 25(2). OBJECTIVE: Electrical signaling along the endothelium underlies spreading vasodilation and blood flow control. We use mathematical modeling to determine the electrical properties of the endothelium and gain insight into the biophysical determinants of electrical conduction. METHODS: Electrical conduction data along endothelial tubes (40 μm wide, 2.5 mm long) isolated from mouse skeletal muscle resistance arteries were analyzed using cable equations and a multicellular computational model. RESULTS: Responses to intracellular current injection attenuate with an axial length constant (λ) of 1.2-1.4 mm. Data were fitted to estimate the axial (ra ; 10.7 MΩ/mm) and membrane (rm ; 14.5 MΩ·mm) resistivities, EC membrane resistance (Rm ; 12 GΩ), and EC-EC coupling resistance (Rgj ; 4.5 MΩ) and predict that stimulation of ≥30 neighboring ECs is required to elicit 1 mV of hyperpolarization at distance = 2.5 mm. Opening Ca2+ -activated K+ channels (KCa ) along the endothelium reduced λ by up to 55%. CONCLUSIONS: High Rm makes the endothelium sensitive to electrical stimuli and able to conduct these signals effectively. Whereas the activation of a group of ECs is required to initiate physiologically relevant hyperpolarization, this requirement is increased by myoendothelial coupling and KCa activation along the endothelium inhibits conduction by dissipating electrical signals. (02/2018)
  • Behringer EJ*, Scallan JP, Jafarnejad M Castorena-Gonzalez JA, Zawieja SD, Moore Jr. JE, Davis MJ, and Segal SS (2017). Calcium and electrical dynamics in lymphatic endothelium. J Physiol. 595(24): 7347-7368. *Co-first authorship. Comment in “Endothelial tubes: another window into lymphatic function” by Kim A. Dora and Dirk F. Van Helden. J Physiol. 595(24):7267-7268, 2017. KEY POINTS: Endothelial cell function in resistance arteries integrates Ca2+ signalling with hyperpolarization to promote relaxation of smooth muscle cells and increase tissue blood flow. Whether complementary signalling occurs in lymphatic endothelium is unknown. Intracellular calcium and membrane potential were evaluated in endothelial cell tubes freshly isolated from mouse collecting lymphatic vessels of the popliteal fossa. Resting membrane potential measured using intracellular microelectrodes averaged ∼-70 mV. Stimulation of lymphatic endothelium by acetylcholine or a TRPV4 channel agonist increased intracellular Ca2+ with robust depolarization. Findings from Trpv4-/- mice and with computational modelling suggest that the initial mobilization of intracellular Ca2+ leads to influx of Ca2+ and Na+ through TRPV4 channels to evoke depolarization. Lymphatic endothelial cells lack the Ca2+ -activated K+ channels present in arterial endothelium to generate endothelium-derived hyperpolarization. Absence of this signalling pathway with effective depolarization may promote rapid conduction of contraction along lymphatic muscle during lymph propulsion. ABSTRACT: Subsequent to a rise in intracellular Ca2+ ([Ca2+ ]i ), hyperpolarization of the endothelium coordinates vascular smooth muscle relaxation along resistance arteries during blood flow control. In the lymphatic vasculature, collecting vessels generate rapid contractions coordinated along lymphangions to propel lymph, but the underlying signalling pathways are unknown. We tested the hypothesis that lymphatic endothelial cells (LECs) exhibit Ca2+ and electrical signalling properties that facilitate lymph propulsion. To study electrical and intracellular Ca2+ signalling dynamics in lymphatic endothelium, we excised collecting lymphatic vessels from the popliteal fossa of mice and removed their muscle cells to isolate intact LEC tubes (LECTs). Intracellular recording revealed a resting membrane potential of ∼-70 mV. Acetylcholine (ACh) increased [Ca2+ ]i with a time course similar to that observed in endothelium of resistance arteries (i.e. rapid initial peak with a sustained 'plateau'). In striking contrast to the endothelium-derived hyperpolarization (EDH) characteristic of arteries, LECs depolarized (>15 mV) to either ACh or TRPV4 channel activation. This depolarization was facilitated by the absence of Ca2+ -activated K+ (KCa ) channels as confirmed with PCR, persisted in the absence of extracellular Ca2+ , was abolished by LaCl3 and was attenuated ∼70% in LECTs from Trpv4-/- mice. Computational modelling of ion fluxes in LECs indicated that omitting K+ channels supports our experimental results. These findings reveal novel signalling events in LECs, which are devoid of the KCa activity abundant in arterial endothelium. Absence of EDH with effective depolarization of LECs may promote the rapid conduction of contraction waves along lymphatic muscle during lymph propulsion. (12/2017)
  • Behringer EJ* and Segal SS (2017). Impact of aging on calcium signaling and membrane potential in endothelium of resistance arteries: Role for mitochondria. J Gerontol A Biol Sci Med Sci. 72(12), 1627-1637. *Corresponding author The integral role of the endothelium during the coordination of blood flow throughout vascular resistance networks has been recognized for several decades now. Early examination of the distinct anatomy and physiology of the endothelium as a signaling conduit along the vascular wall has prompted development and application of an intact endothelial "tube" study model isolated from rodent skeletal muscle resistance arteries. Vasodilatory signals such as increased endothelial cell (EC) Ca2+ ([Ca2+ ]i ) and hyperpolarization take place in single ECs while shared between electrically coupled ECs through gap junctions up to distances of millimeters (≥2 mm). The small- and intermediate-conductance Ca2+ activated K+ (SKCa /IKCa or KCa 2.3/KCa 3.1) channels function at the interface of Ca2+ signaling and hyperpolarization; a bidirectional relationship whereby increases in [Ca2+ ]i activate SKCa /IKCa channels to produce hyperpolarization and vice versa. Further, the spatial domain of hyperpolarization among electrically coupled ECs can be finely tuned via incremental modulation of SKCa /IKCa channels to balance the strength of local and conducted electrical signals underlying vasomotor activity. Multifunctional properties of the voltage-insensitive SKCa /IKCa channels of resistance artery endothelium may be employed for therapy during the aging process and development of vascular disease. (11/2017) (link)
  • Behringer EJ (2017). Calcium and electrical signaling in arterial endothelial tubes: New insights into cellular physiology and cardiovascular function. Microcirculation 24(3). The integral role of the endothelium during the coordination of blood flow throughout vascular resistance networks has been recognized for several decades now. Early examination of the distinct anatomy and physiology of the endothelium as a signaling conduit along the vascular wall has prompted development and application of an intact endothelial "tube" study model isolated from rodent skeletal muscle resistance arteries. Vasodilatory signals such as increased endothelial cell (EC) Ca2+ ([Ca2+ ]i ) and hyperpolarization take place in single ECs while shared between electrically coupled ECs through gap junctions up to distances of millimeters (≥2 mm). The small- and intermediate-conductance Ca2+ activated K+ (SKCa /IKCa or KCa 2.3/KCa 3.1) channels function at the interface of Ca2+ signaling and hyperpolarization; a bidirectional relationship whereby increases in [Ca2+ ]i activate SKCa /IKCa channels to produce hyperpolarization and vice versa. Further, the spatial domain of hyperpolarization among electrically coupled ECs can be finely tuned via incremental modulation of SKCa /IKCa channels to balance the strength of local and conducted electrical signals underlying vasomotor activity. Multifunctional properties of the voltage-insensitive SKCa /IKCa channels of resistance artery endothelium may be employed for therapy during the aging process and development of vascular disease. (04/2017) (link)
  • Behringer EJ and Segal SS (2015). Membrane potential governs calcium influx into microvascular endothelium: Integral role for muscarinic receptor activation. J Physiol. 593(20), 4531-4548.  In resistance arteries, coupling a rise of intracellular calcium concentration ([Ca(2+)]i) to endothelial cell hyperpolarization underlies smooth muscle cell relaxation and vasodilatation, thereby increasing tissue blood flow and oxygen delivery. A controversy persists as to whether changes in membrane potential (V(m)) alter endothelial cell [Ca(2+)]i. We tested the hypothesis that V(m) governs [Ca(2+)]i in endothelium of resistance arteries by performing Fura-2 photometry while recording and controlling V(m) of intact endothelial tubes freshly isolated from superior epigastric arteries of C57BL/6 mice. Under resting conditions, [Ca(2+)]i did not change when V(m) shifted from baseline (∼-40 mV) via exposure to 10 μM NS309 (hyperpolarization to ∼-80 mV), via equilibration with 145 mm [K(+)]o (depolarization to ∼-5 mV), or during intracellular current injection (±0.5 to 5 nA, 20 s pulses) while V(m) changed linearly between ∼-80 mV and +10 mV. In contrast, during the plateau (i.e. Ca(2+) influx) phase of the [Ca(2+)]i response to approximately half-maximal stimulation with 100 nm ACh (∼EC50), [Ca(2+)]i increased as V(m) hyperpolarized below -40 mV and decreased as V(m) depolarized above -40 mV. The magnitude of [Ca(2+)]i reduction during depolarizing current injections correlated with the amplitude of the plateau [Ca(2+)]i response to ACh. The effect of hyperpolarization on [Ca(2+)]i was abolished following removal of extracellular Ca(2+), was enhanced subtly by raising extracellular [Ca(2+)] from 2 mm to 10 mm and was reduced by half in endothelium of TRPV4(-/-) mice. Thus, during submaximal activation of muscarinic receptors, V(m) can modulate Ca(2+) entry through the plasma membrane in accord with the electrochemical driving force. (10/2015)
  • Socha MJ, Boerman EM, Behringer EJ, Shaw RL, Domeier TL, and Segal SS (2015). Advanced age protects microvascular endothelium from aberrant Ca2+ influx and cell death induced by hydrogen peroxide. J Physiol. 593(9), 2155-2169. KEY POINTS: Calcium signalling in endothelial cells of resistance arteries is integral to blood flow regulation. Oxidative stress and endothelial dysfunction can prevail during advanced age and we questioned how calcium signalling may be affected. Intact endothelium was freshly isolated from superior epigastric arteries of Young (∼4 months) and Old (∼24 months) male C57BL/6 mice. Under resting conditions, with no difference in intracellular calcium levels, hydrogen peroxide (H2 O2 ) availability was ∼1/3 greater in endothelium of Old mice while vascular catalase activity was reduced by nearly half. Compared to Old, imposing oxidative stress (200 μm H2 O2 ) for 20 min increased intracellular calcium to 4-fold greater levels in endothelium of Young in conjunction with twice the calcium influx. Prolonged (60 min) exposure to H2 O2 induced 7-fold greater cell death in endothelium of Young. Microvascular adaptation to advanced age may protect endothelial cells during elevated oxidative stress to preserve functional viability of the intima. ABSTRACT: Endothelial cell Ca(2+) signalling is integral to blood flow control in the resistance vasculature yet little is known of how its regulation may be affected by advancing age. We tested the hypothesis that advanced age protects microvascular endothelium by attenuating aberrant Ca(2+) signalling during oxidative stress. Intact endothelial tubes (width, ∼60 μm; length, ∼1000 μm) were isolated from superior epigastric arteries of Young (3-4 months) and Old (24-26 months) male C57BL/6 mice and loaded with Fura-2 dye to monitor [Ca(2+) ]i . At rest there was no difference in [Ca(2+) ]i between age groups. Compared to Young, the [Ca(2+) ]i response to maximal stimulation with acetylcholine (3 μm, 2 min) was ∼25% greater in Old, confirming signalling integrity with advanced age. Basal H2 O2 availability was ∼33% greater in Old while vascular catalase activity was reduced by half. Transient exposure to elevated H2 O2 (200 μm, 20 min) progressively increased [Ca(2+) ]i to ∼4-fold greater levels in endothelium of Young versus Old. With no difference between age groups at rest, Mn(2+) quench of Fura-2 fluorescence revealed 2-fold greater Ca(2+) influx in Young during elevated H2 O2 ; this effect was attenuated by ∼75% using ruthenium red (5 μm) as a broad-spectrum inhibitor of transient receptor potential channels. Prolonged exposure to H2 O2 (200 μm, 60 min) induced ∼7-fold greater cell death in endothelium of Young versus Old. Thus, microvascular endothelium can adapt to advanced age by reducing Ca(2+) influx during elevated oxidative stress. Protection from cell death during oxidative stress will sustain endothelial integrity during ageing. (05/2015)
  • Behringer EJ, Shaw RL, Westcott EB, Socha MJ, and Segal SS (2013). Aging impairs electrical conduction along endothelium of resistance arteries through enhanced Ca2+-activated K+ channels activation. Arterioscler Thromb Vasc Biol. 33, 1892-1901.  OBJECTIVE: Intercellular conduction of electrical signals underlies spreading vasodilation of resistance arteries. Small- and intermediate-conductance Ca(2+)-activated K(+) channels of endothelial cells serve a dual function by initiating hyperpolarization and modulating electrical conduction. We tested the hypothesis that regulation of electrical signaling by small- and intermediate-conductance Ca(2+)-activated K(+) channels is altered with advancing age. APPROACH AND RESULTS: Intact endothelial tubes (60 µm wide; 1-3 mm long) were freshly isolated from male C57BL/6 mouse (Young: 4-6 months; Intermediate: 12-14 months; Old: 24-26 months) superior epigastric arteries. Using dual intracellular microelectrodes, current was injected (± 0.1-3 nA) at site 1 while recording membrane potential (Vm) at site 2 (separation distance: 50-2000 µm). Across age groups, greatest differences were observed between Young and Old. Resting Vm in Old (-38 ± 1 mV) was more negative (P<0.05) than Young (-30 ± 1 mV). Maximal hyperpolarization to both direct (NS309) and indirect (acetylcholine) activation of small- and intermediate-conductance Ca(2+)-activated K(+) channels was sustained (ΔVm ≈-40 mV) with age. The length constant (λ) for electrical conduction was reduced (P<0.05) from 1630 ± 80 µm (Young) to 1320 ± 80 µm (Old). Inhibiting small- and intermediate-conductance Ca(2+)-activated K(+) channels with apamin+charybdotoxin or scavenging hydrogen peroxide (H2O2) with catalase improved electrical conduction (P<0.05) in Old. Exogenous H2O2 (200 µmol/L) in Young evoked hyperpolarization and impaired electrical conduction; these effects were blocked by apamin+charybdotoxin. CONCLUSIONS: Enhanced current loss through Ca2+-activated K+ channel activation impairs electrical conduction along the endothelium of resistance arteries with aging. Attenuating the spatial domain of electrical signaling will restrict the spread of vasodilation and thereby contribute to blood flow limitations associated with advanced age. (08/2013)
  • Behringer EJ and Segal SS (2012). Spreading the signal for vasodilatation: Implications for skeletal muscle blood flow control and the effects of aging. J. Physiol. 590 (Pt 24), 6277-6284. Blood flow control requires coordinated contraction and relaxation of smooth muscle cells (SMCs) along and among the arterioles and feed arteries that comprise vascular resistance networks. Whereas smooth muscle contraction of resistance vessels is enhanced by noradrenaline release along perivascular sympathetic nerves, the endothelium is integral to coordinating smooth muscle relaxation. Beyond producing nitric oxide in response to agonists and shear stress, endothelial cells (ECs) provide an effective conduit for conducting hyperpolarization along vessel branches and into surrounding SMCs through myoendothelial coupling. In turn, bidirectional signalling from SMCs into ECs enables the endothelium to moderate adrenergic vasoconstriction in response to sympathetic nerve activity. This review focuses on the endothelium as the cellular pathway that coordinates spreading vasodilatation. We discuss the nature and regulation of cell-to-cell coupling through gap junctions, bidirectional signalling between ECs and SMCs, and how oxidative stress during ageing may influence respective signalling pathways. Our recent findings illustrate the role of small (SK(Ca)) and intermediate (IK(Ca)) Ca(2+) activated K(+) channels as modulators of electrical conduction along the endothelium. Gaps in current understanding indicate the need to determine mechanisms that regulate intracellular Ca(2+) homeostasis and ion channel activation in the resistance vasculature with advancing age. (12/2012)
  • Socha MJ, Domeier TL, Behringer EJ, Segal SS (2012). Coordination of intercellular Ca2+ signaling in endothelial cell tubes of resistance arteries. Microcirculation. 19(8), 757-770. OBJECTIVE: To test the hypothesis that Ca(2+) responses to GPCR activation are coordinated between neighboring ECs of resistance arteries. METHODS: EC tubes were freshly isolated from superior epigastric arteries of C57BL/6 mice. Intercellular coupling was tested using microinjection of propidium iodide. Following loading with fluo-4 dye, intracellular Ca(2+) responses to ACh were imaged with confocal microscopy. RESULTS: Cell-to-cell transfer of propidium iodide confirmed functional GJCs. A 1 μm ACh stimulus evoked Ca(2+) responses (9.8 ± 0.8/min, F/F(0) = 3.11 ± 0.2) which pseudo-line-scan analysis revealed as composed of Ca(2+) waves and spatially restricted Ca(2+) release events. A 100 nm ACh stimulus induced Ca(2+) responses of lower frequency (4.5 ± 0.7/min) and amplitude (F/F(0) = 1.95 ± 0.11) composed primarily of spatially restricted events. The time interval between Ca(2+) waves in adjacent cells (0.79 ± 0.12 s) was shorter (p < 0.05) than that between nonadjacent cells (1.56 ± 0.25 s). Spatially restricted Ca(2+) release events had similar frequencies and latencies between adjacent and nonadjacent cells. Inhibiting intracellular Ca(2+) release with 2-APB, Xestospongin C or thapsigargin eliminated Ca(2+) responses. CONCLUSIONS: With moderate GPCR stimulation, localized Ca(2+) release events predominate among cells. Greater GPCR stimulation evokes coordinated intercellular Ca(2+) waves via the ER. Calcium signaling during GPCR activation is complex among cells, varying with stimulus intensity and proximity to actively signaling cells. (11/2012)
  • Behringer EJ and Segal SS (2012). Tuning electrical conduction along endothelial cell tubes through Ca2+-activated K+ channels. Circ Res. 110, 1311-1321. RATIONALE: Electrical conduction through gap junction channels between endothelial cells of resistance vessels is integral to blood flow control. Small and intermediate-conductance Ca(2+)-activated K(+) channels (SK(Ca)/IK(Ca)) initiate electrical signals in endothelial cells, but it is unknown whether SK(Ca)/IK(Ca) activation alters signal transmission along the endothelium. OBJECTIVE: We tested the hypothesis that SK(Ca)/IK(Ca) activity regulates electrical conduction along the endothelium of resistance vessels. METHODS AND RESULTS: Freshly isolated endothelial cell tubes (60 μm wide; 1-3 mm long; cell length, ≈35 μm) from mouse skeletal muscle feed (superior epigastric) arteries were studied using dual intracellular microelectrodes. Current was injected (±0.1-3 nA) at site 1 while recording membrane potential (V(m)) at site 2 (separation distance=50-2000 μm). SK(Ca)/IK(Ca) activation (NS309, 1 μmol/L) reduced the change in V(m) along endothelial cell tubes by ≥50% and shortened the electrical length constant (λ) from 1380 to 850 μm (P<0.05) while intercellular dye transfer (propidium iodide) was maintained. Activating SK(Ca)/IK(Ca) with acetylcholine or SKA-31 also reduced electrical conduction. These effects of SK(Ca)/IK(Ca) activation persisted when hyperpolarization (>30 mV) was prevented with 60 mmol/L [K(+)](o). Conversely, blocking SK(Ca)/IK(Ca) (apamin+charybdotoxin) depolarized cells by ≈10 mV and enhanced electrical conduction (ie, changes in V(m)) by ≈30% (P<0.05). CONCLUSIONS: These findings illustrate a novel role for SK(Ca)/IK(Ca) activity in tuning electrical conduction along the endothelium of resistance vessels by governing signal dissipation through changes in membrane resistance. Voltage-insensitive ion channels can thereby tune intercellular electrical signaling independent from gap junction channels. (05/2012)
  • Behringer EJ, Socha MJ, Polo-Parada L, Segal SS (2012). Electrical conduction along endothelial cell tubes from mouse feed arteries: confounding actions of glycyrrhetinic acid derivatives. Br J Pharmacol. 166(2), 774-787. BACKGROUND AND PURPOSE: Electrical conduction along endothelium of resistance vessels has not been determined independently of the influence of smooth muscle, surrounding tissue or blood. Two interrelated hypotheses were tested: (i) Intercellular conduction of electrical signals is manifest in endothelial cell (EC) tubes; and (ii) Inhibitors of gap junction channels (GJCs) have confounding actions on EC electrical and Ca(2+) signalling. EXPERIMENTAL APPROACH: Intact EC tubes were isolated from abdominal muscle feed (superior epigastric) arteries of C57BL/6 mice. Hyperpolarization was initiated with indirect (ACh) and direct (NS309) stimulation of intermediate- and small-conductance Ca(2+) -activated K(+) channels (IK(Ca) /SK(Ca) ). Remote membrane potential (V(m) ) responses to intracellular current injection defined the length constant (λ) for electrical conduction. Dye coupling was evaluated following intracellular microinjection of propidium iodide. Intracellular Ca(2+) dynamics were determined using Fura-2 photometry. Carbenoxolone (CBX) or β-glycyrrhetinic acid (βGA) was used to investigate the role of GJCs. KEY RESULTS: Steady-state V(m) of ECs was -25 mV. ACh and NS309 hyperpolarized ECs by -40 and -60 mV respectively. Electrical conduction decayed monoexponentially with distance (λ∼1.4 mm). Propidium iodide injected into one EC spread into surrounding ECs. CBX or βGA inhibited dye transfer, electrical conduction and EC hyperpolarization reversibly. Both agents elevated resting Ca(2+) while βGA inhibited responses to ACh. CONCLUSIONS AND IMPLICATIONS: Individual cells were effectively coupled to each other within EC tubes. Inhibiting GJCs with glycyrrhetinic acid derivatives blocked hyperpolarization mediated by IK(Ca) /SK(Ca) channels, regardless of Ca(2+) signalling, obviating use of these agents in distinguishing key determinants of electrical conduction along the endothelium. (05/2012)
  • Socha MJ*, Behringer EJ*, Segal SS. (2012). Calcium and electrical signaling along endothelium of the resistance vasculature. Basic Clin Pharmacol Toxicol. 110(1), 80-86. *Equal contribution This MiniReview is focused on the nature of intercellular signalling along the endothelium that helps to co-ordinate blood flow control in vascular resistance networks. Vasodilation initiated by contracting skeletal muscle ascends from arterioles within the tissue to encompass resistance arteries upstream and thereby increase blood flow during exercise. In resistance vessels, acetylcholine microiontophoresis or intracellular current injection initiates hyperpolarization that conducts through gap junction channels (GJCs) along the vessel wall resulting in conducted vasodilation (CVD). Both ascending vasodilation and CVD are eliminated with endothelial cell (EC) disruption, pointing to common signalling events and mutual dependence upon EC integrity. As demonstrated by electrical coupling and dye transfer during intracellular recording, their longitudinal orientation and robust expression of GJCs enable ECs to play a predominant role in CVD. Once conduction is initiated, a major interest centres on whether CVD is purely passive or involves additional 'active' signalling events. Here, we discuss components for Ca²? and electrical signalling with an emphasis on intercellular coupling through endothelial GJCs. We stress the importance of understanding relationships between intracellular Ca²? dynamics, EC hyperpolarization and CVD while integrating findings from isolated ECs into more complex interactions in vivo. Whereas endothelial dysfunction accompanies cardiovascular disease and the components of intra- and inter-cellular signalling are increasingly well defined, little is known of how Ca²? signalling and electrical conduction along microvascular endothelium are altered in diseased states. Thus, greater insight into how these relationships are governed and interact is a key goal for continued research efforts. (01/2012)
  • Behringer EJ, Leite LD, Buchholz NE, Keeney MG, Pearce WJ, Vanterpool CK, Wilson SM, Buchholz JN (2009). Maturation and long-term hypoxia alters Ca2+-induced Ca2+ release in sheep cerebrovascular sympathetic neurons. J Appl Physiol. 107(4), 1223-1234. The contribution of sympathetic nerves arising from the superior cervical ganglia (SCG) toward the growth and function of cerebral blood vessels is pertinent throughout maturation as well as in response to cardiovascular stress imposed by high-altitude long-term hypoxia (LTH). The function of SCG sympathetic neurons is dependent on intracellular Ca2+ concentration ([Ca2+](i)) signaling, which is strongly influenced by a process known as Ca2+-induced Ca2+ release (CICR) from the smooth endoplasmic reticulum (SER). In this study, we used the sheep SCG neuronal model to test the hypotheses that maturation decreases CICR and high-altitude LTH depresses CICR in fetal SCG neurons but not in those of the adult. We found that the contribution of CICR to electric field stimulation (EFS)-evoked [Ca2+] i transients was greatest in SCG cells from normoxic fetuses and was abolished by LTH. The decline in CICR was associated with a reduction in sarco(endo) plasmic reticulum Ca2+-ATPase (SERCA) function in fetal SCG cells during LTH, reducing SER Ca2+ levels below the threshold needed for the coupling of Ca2+ influx and CICR. With respect to the maturation from the fetus to adult, the decrease in CICR may reflect both a reduction in the levels of ryanodine receptor isoforms 2 and 3 and SERCA function. In response to LTH and in contrast to the fetus, CICR function in adult SCG cells is maintained and may reflect alterations in other mechanisms that modulate the CICR process. As CICR is instrumental in the function of sympathetic neurons within the cerebrovasculature, the loss of this signaling mechanism in the fetus may have consequences for the adaptation to LTH in terms of fetal susceptibility to vascular insults. (07/2009) (link)
  • Behringer EJ, Vanterpool CK, Pearce WJ, Wilson SM, & Buchholz JN (2009). Advancing Age Alters the Contribution of Calcium Release From Smooth Endoplasmic Reticulum Stores in Superior Cervical Ganglion Cells. J Gerontol A Biol Sci Med Sci. 64(1), 34-44. In superior cervical ganglion (SCG) neurons calcium-induced calcium release (CICR), mediated by ryanodine receptors (RyRs), contributes to stimulation-evoked intracellular calcium ([Ca(2+)](i)) transients. Hypothesis: The contribution of CICR to electrical field stimulation (EFS)-evoked [Ca(2+)](i) transients in SCG cells declines with senescence and may be partially recovered in the presence of caffeine. We measured EFS-evoked [Ca(2+)](i) transients in isolated fura-2-loaded SCG cells from Fischer-344 rats aged 6, 12, and 24 months with either the RyR antagonist ryanodine to block the contribution of CICR to [Ca(2+)](i) transients or caffeine to sensitize CICR to EFS. EFS-evoked [Ca(2+)](i) transients increased from 6 to 12 months and declined at 24 months and ryanodine decreased [Ca(2+)](i) transients in SCG cells from 6- and 12-monthold animals only. Caffeine significantly increased EFS-evoked [Ca(2+)](i) transients in all age groups. These data suggest that CICR declines with senescence and residual CICR function may be reclaimed in senescent cells with caffeine. (01/2009) (link)
  • Buchholz JN, Behringer EJ, Pottorf BJ, Pearce WJ and Vanterpool CK (2007). Age–dependent changes in Ca2+ homeostasis in peripheral neurons:  implications for changes in function. Aging Cell, 6(3), 285-296. Calcium ions represent universal second messengers within neuronal cells integrating multiple cellular functions, such as release of neurotransmitters, gene expression, proliferation, excitability, and regulation of cell death or apoptotic pathways. The magnitude, duration and shape of stimulation-evoked intracellular calcium ([Ca2+]i) transients are determined by a complex interplay of mechanisms that modulate stimulation-evoked rises in [Ca2+]i that occur with normal neuronal function. Disruption of any of these mechanisms may have implications for the function and health of peripheral neurones during the aging process. This review focuses on the impact of advancing age on the overall function of peripheral adrenergic neurones and how these changes in function may be linked to age-related changes in modulation of [Ca2+]i regulation. The data in this review suggest that normal aging in peripheral autonomic neurones is a subtle process and does not always result in dramatic deterioration in their function. We present studies that support the idea that in order to maintain cell viability peripheral neurones are able to compensate for an age-related decline in the function of at least one of the neuronal calcium-buffering systems, smooth endoplasmic reticulum calcium ATPases, by increased function of other calcium-buffering systems, namely, the mitochondria and plasmalemma calcium extrusion. Increased mitochondrial calcium uptake may represent a 'weak point' in cellular compensation as this over time may contribute to cell death. In addition, we present more recent studies on [Ca2+]i regulation in the form of the modulation of release of calcium from smooth endoplasmic reticulum calcium stores. These studies suggest that the contribution of the release of calcium from smooth endoplasmic reticulum calcium stores is altered with age through a combination of altered ryanodine receptor levels and modulation of these receptors by neuronal nitric oxide containing neurones. (06/2007)

Books and Chapters

  • Buchholz JN, Behringer EJ (Editors). Calcium and Signal Transduction. Physiology Series, Volume 1. London, UK: Intech Open; 2019:1-192. ISBN: 978-1-78984-249-4. (01/2018 - 01/2019)
  • Behringer EJ, Segal SS. Ion channels in control of blood flow: electrical conduction along endothelium of resistance arteries. In: Vascular Ion Channels in Physiology and Disease. Cham, Switzerland: Springer; 2016:79–100. ISBN: 978-3319296333.    (01/2016 - 2018)
  • Buchholz JN, Pottorf WJ, Vanterpool CK, Behringer EJ and Duckles SP (2012). Senescence, Chapter title: Calcium Regulation in Neuronal Function with Advancing Age: Limits of Homeostasis. Rijeka, Croatia: InTech; 2012: 531-558. ISBN: 978-953-308-28-6. (01/2012 - 2018)

Abstract

  • Local: 1.   Behringer EJ, Leite LD, Buchholz NE, Keeney M, Pearce WJ and Buchholz JN. The impact of development and long-term hypoxia on molecular modulators of calcium-induced calcium release in sheep sympathetic neurons.  Loma Linda Basic Sciences Symposium 2006.  2.   Behringer EJ, Vanterpool CK, Pearce WJ and Buchholz JN. Advancing age alters the contribution of release of calcium from internal stores to stimulation-evoked calcium transients to stimulation-evoked influx in rat superior cervical ganglia.  Loma Linda Basic Sciences Symposium 2007.  3.   Behringer EJ, Leite LD, Buchholz NE, Keeney MG, Pearce WJ and Buchholz JN. Development and long-term hypoxia alters calcium-induced calcium release in sheep cerebrovascular neurons.  Loma Linda Basic Sciences Symposium 2008.  4.   Behringer EJ, Polo-Parada L, Jackson WF, Segal SS. IKCa/SKCa channels modulate electrical conduction along microvascular endothelial tubes. Cardiovascular Day 2011, University of Missouri—Columbia.  5.   Behringer EJ and Segal SS. Aging restricts electrical signaling along endothelial tubes via enhanced activation of SKCa/IKCa channels: role for oxidative stress. Cardiovascular Day 2013, University of Missouri—Columbia.  6.   Behringer EJ and Segal SS. Modulating Ca2+ entry into endothelial tubes by controlling membrane potential during muscarinic receptor activation. Cardiovascular Day, 2014. University of Missouri—Columbia.  7.   Hickey B, Calderon B, Bowman D, Hewitt C, Behringer E. Mitochondrial regulation of calcium and electrical signaling in the cardiovascular and nervous systems with advancing age. Center for Health Disparities & Molecular Medicine Symposium (August 3, 2016). Loma Linda University, Loma Linda, CA.  8.   Stoll S, Behringer E, and Qiu H. The valosin-containing protein inhibits the mitochondrial permeability transition pore opening via inducible nitric oxide synthase in the heart. 19th Annual Research Symposium jointly with the 5th Annual Inland Empire Stem Cell Consortium Symposium (November 8, 2016).  9.   Thomas E, Tsai D, Hewitt C, Buchholz J, Behringer E. Expression of the mitochondrial calcium uniporter in mouse hippocampus and cortex with advancing age. Center for Health Disparities & Molecular Medicine Symposium (August 2, 2017). Loma Linda University, Loma Linda, CA.  10.  Nye P, Kumar M, Hakim M, Behringer E. Real time PCR analysis of cerebrovascular endothelial and smooth muscle cell biomarkers with advancing age. Center for Health Disparities & Molecular Medicine Symposium (August 2, 2017). Loma Linda University, Loma Linda, CA.  11. Hakim MA, Buchholz JN, Behringer EJ. Electrical dynamics of isolated cerebral and skeletal muscle endothelial tubes: differential roles of G-Protein coupled receptors and K+ channels. Loma Linda Basic Sciences Symposium 2017 (November 2, 2017).  12. White J, Nye P, and Behringer EJ. Genetic Expression of cerebrovascular endothelial GPCRs, ion channels, and connexins during advancing age and Alzheimer’s disease. Center for Health Disparities & Molecular Medicine Symposium (August 1, 2018). Loma Linda University, Loma Linda, CA.  13. Nye P and Behringer EJ. Genetic expression profiles of cerebrovascular endothelium during development of Alzheimer’s disease. Loma Linda Basic Sciences 21st Symposium (November 1, 2018). Loma Linda University, Loma Linda, CA.  14. Hakim MA, Buchholz JN, and Behringer EJ. Calcium and electrical dynamics of cerebral arterial endothelium during development of Alzheimer’s disease. Loma Linda Basic Sciences 21st Symposium (November 1, 2018). Loma Linda University, Loma Linda, CA.  15. Stoll S, Behringer E, Qiu H. The valosin-containing protein resists mitochondrial calcium overload by reducing calcium uptake. Loma Linda Basic Sciences 21st Symposium (November 1, 2018). Loma Linda University, Loma Linda, CA.16. Cedeño L, Chum PP, Buchholz JN, Behringer EJ. Genetic expression of endothelium mitochondrial calcium ion channels and antioxidant enzymes of the brain during Alzheimer’s disease. Center for Health Disparities & Molecular Medicine Symposium (August 7, 2019). Loma Linda University, Loma Linda, CA.17. Cellini JM, Hewitt CW, Buchholz JN, Behringer EJ. Norepinephrine levels in the mouse brain with Alzheimer’s disease. Center for Health Disparities & Molecular Medicine Symposium (August 7, 2019). Loma Linda University, Loma Linda, CA.18. Hakim MA, Behringer EJ. Alzheimer’s disease as a condition of accelerated cerebrovascular aging. Loma Linda Basic Sciences 22nd Symposium (October 31, 2019). Loma Linda University, Loma Linda, CA. 19. Hakim MA & Behringer EJ. Removal of membrane cholesterol selectively restores KIR channel function in brain endothelium during Alzheimer’s disease. Loma Linda Basic Sciences 23rd Symposium in partnership with the Inland Empire Stem Cell Consortium (October 29, 2020). Loma Linda University, Loma Linda, CA. 20. Chum PP & Behringer EJ. Cerebrovascular miRNA expression profile during development of Alzheimer’s disease*. Loma Linda Basic Sciences 23rd Symposium in partnership with the Inland Empire Stem Cell Consortium (October 29, 2020). Loma Linda University, Loma Linda, CA. *Competitively selected for the School of Medicine (SOM)/Annual Postgraduate Convention (APC) 2021 poster session (3/4-3/8/2021). 21. Hakim MA*, Pires PW, Behringer EJ. Isolation and functional resolution of arteriolar endothelium of mouse brain parenchyma. Loma Linda Basic Sciences 24th Symposium (November 4, 2021). Loma Linda University, Loma Linda, CA.*Selected flash talk speaker 22. Samardzija MK, Solis SR, Chum PP, Behringer EJ. Role of endothelial specific miRNAs during development of Alzheimer’s disease. Center for Health Disparities & Molecular Medicine Symposium (August 3, 2022). Loma Linda University, Loma Linda, CA. 23. Solis SR, Chum PP, Behringer EJ. Cerebrovascular miRNAs governing endothelial cell growth, structure, and function indicate Alzheimer’s disease pathogenesis. Center for Health Disparities & Molecular Medicine Symposium (August 3, 2022). Loma Linda University, Loma Linda, CA. 24. Miot FEL & Behringer EJ.  Computational modeling of neurovascular ion channel activity. Loma Linda Basic Sciences 25th Symposium (October 27, 2022). Loma Linda University, Loma Linda, CA. 25. Bishara MA, Solis SR, Chum PP, Behringer EJ. Cerebrovascular miRNA & mRNA targets mark onset of Alzheimer’s disease. Loma Linda Basic Sciences 25th Symposium (October 27, 2022). Loma Linda University, Loma Linda, CA. (Present)
  • National/International Conferences: 1.   Behringer EJ, Vanterpool CK, Pearce WJ and Buchholz JN.  Late maturation and advancing age alter the contribution of release of calcium from internal stores to stimulation-evoked calcium transients.  Society for Neuroscience 2006 (80.5/KK12).   2.   Buchholz JN, Vanterpool CK, Pearce WJ and Behringer EJ. Advancing age alters the contribution of release of calcium from internal stores to stimulation-evoked calcium transients to stimulation-evoked influx in rat superior cervical ganglia.  Experimental Biology 2007. FASEB J 21:A1350, 2007.  3.   Behringer EJ, Vanterpool CK, Pearce WJ and Buchholz JN. Impact of advancing age on caffeine-mediated sensitization of calcium release in superior cervical ganglion cells.  Experimental Biology 2008. FASEB J 22:1126.7, 2008. 4.   Behringer EJ, Leite LD, Buchholz NE, Keeney MG, Pearce WJ and Buchholz JN. Development and long-term hypoxia alters calcium-induced calcium release in sheep cerebrovascular neurons.  Society for Neuroscience 2008 (482.4/RR37). 5.   Behringer EJ,  Polo-Parada L, Jackson WF, Segal SS. Glycyrrhetinic acid derivatives block hyperpolarization concomitant with intercellular coupling along microvascular endothelial tubes. Experimental Biology 2011. FASEB J 25:817.5, 2011. 6.  Behringer EJ, Socha MJ, Jackson WF, Segal SS. IKCa/SKCa channels modulate electrical conduction along microvascular endothelial tubes. Peer-reviewed abstract accepted by the 10th International Symposium on Resistance Arteries (ISRA; Rebild Bakker, Denmark, 5/ 2011). 7.   Behringer EJ and Segal SS. Tuning electrical conduction along endothelial cell tubes via Ca2+-activated K+ channels. Experimental Biology 2012. FASEB J 26:1058.12, 2012. 8.   Behringer EJ and Segal SS. Aging impairs electrical conduction along resistance artery endothelium via enhanced signal dissipation through KCa channels. Experimental Biology 2012. FASEB J 26:861.2, 2012. 9.   Behringer EJ. Young Investigator Session: Aging impairs electrical conduction along endothelial tubes via activation of KCa channels by reactive oxygen species. Joint meeting of the British Microcirculation Society & the Microcirculatory Society, Inc. 2012. 10. Behringer EJ and Segal SS. Aging restricts electrical signaling along endothelial tubes via enhanced activation of SKCa/IKCa channels: role for oxidative stress. Annual meeting of the Biophysical Society 2013. Biophys J., 104(2):493a, 2013. 11. Behringer EJ and Segal SS. Altered electrical reactivity of endothelial tubes with aging: Role of mitochondria and Ca2+-activated K+ channels. Experimental Biology 2013. FASEB J 27:679.1, 2013. 12. Behringer EJ, Scallan JP, Davis MJ, and Segal SS. Depolarization of collecting lymphatic endothelium with acetylcholine or TRPV4 activation. Experimental Biology 2013. FASEB J 27:678.3, 2013. 13. Behringer EJ, Socha MJ, Westcott EB and Segal SS. Sustained calcium release and hyperpolarization in microvascular endothelium with advanced age. Joint meeting of the North American Vascular Biology Organization (NAVBO) and the Microcirculatory Society (MCS), October 20-24, 2013. 14. Behringer EJ and Segal SS. Modulating Ca2+ entry into endothelial tubes by controlling membrane potential during muscarinic receptor activation. Experimental Biology 2014. FASEB J 28: 664.7, 2014. 15. Behringer EJ. Impact of aging on calcium and electrical signaling in microvascular endothelium. National Institute on Aging Butler-Williams Scholars Program (formerly known as the NIA Summer Institute). NIH campus, Bethesda, MD, August 4-8, 2014. 16. Behringer EJ and Segal SS. Hyperpolarization enhances calcium influx into endothelium of resistance arteries during muscarinic receptor activation: role of TRPV4 channels. 11th International Symposium on Resistance Arteries (ISRA; Banff, Alberta, Canada, 9/2014). 17. Behringer EJ and Segal SS. Modulating calcium entry into microvascular endothelium by controlling membrane potential during submaximal muscarinic receptor activation. Annual meeting of the Biophysical Society 2015. Biophys J., 108(2):p105a, 2015. 18. Behringer EJ. Impact of aging on calcium and electrical signaling in microvascular endothelium. Ninth Annual Division of Aging Biology New Investigator’s Forum. NIH campus, Bethesda, MD, June 18-19, 2015. 19. Jafarnejad M, Behringer EJ, Scallan JP, Davis MJ, Segal SS, Moore Jr. JE. Mathematical Model of Calcium and Electrical Dynamics in Lymphatic Endothelium. Experimental Biology 2016. FASEB J 30:726.9, 2016. 20. Hakim MA, Buchholz JN, Behringer EJ. Altered intracellular calcium reactivity of cerebral artery endothelial tubes with advancing age. Society for Neuroscience 2017; 11/13/2017. 21. Hakim MA, Buchholz JN, Behringer EJ. Alteration of Calcium and Electrical Dynamics in Cerebrovascular Endothelium During Development of Alzheimer’s disease. Experimental Biology 2019; 4/7/2019.22. Nye PP, Behringer EJ. Genetic Expression Profile of Cerebrovascular Endothelium During Development of Alzheimer’s Disease. Experimental Biology 2019; 4/7/2019.23. Stoll S, Ma B, Behringer EJ, Qiu H. The valosin-containing protein resists pathological cardiac calcium overload via inhibiting mitochondrial calcium uptake. American Heart Association Council on Basic Cardiovascular Sciences 2019.24. Jullienne A, Obenaus A, Lee JB, Behringer E; for the MODEL-AD Consortium. Lifespan magnetic resonance imaging of novel mouse models of Alzheimer’s disease: phenotyping and comparisons to healthy aging. Society for Neuroscience 2019; 10/22/2019.25. Hakim MA & Behringer EJ. Alzheimer’s disease as a condition of accelerated cerebrovascular aging. Bangladesh Medical Association of North America (BMANA) 11th Annual Convention (California Chapter); 2/16/2020.26. Hakim MA & Behringer EJ. Alzheimer’s disease as a condition of accelerated aging of cerebrovascular endothelial function. Experimental Biology 2020; 4/5/2020. 27. Chum PP & Behringer EJ. Cerebrovascular miRNA expression profile during development of Alzheimer’s disease. Experimental Biology 2021. 28. Hakim MA* & Behringer EJ. Removal of membrane cholesterol selectively restores KIR channel function in brain endothelium during Alzheimer’s disease. Experimental Biology 2021. *Author & abstract won the American Physiological Society (APS) Central Nervous System (CNS) & Cell Section 2021 Research Recognition Awards. 29. Behringer EJ, Hakim MA, Blackwell J, Pires PW. Endothelial KIR channel dysfunction in aged cerebral parenchymal arterioles. Experimental Biology 2022. Selected for the APS Wiggers Award topic ("Sex and aging in the microcirculation"; Chair: David Busija) on 4/5/2022.   (Present)