Endothelial alkalinisation inhibits gap junction communication and endothelium‐derived hyperpolarisations in mouse mesenteric arteries

Abstract

Key points• Gap junctions are important for coordination and transfer of signals between cells. Signals initiated in the vascular endothelium can spread through myoendothelial gap junctions and cause relaxation of coupled vascular smooth muscle cells.• The cellular level of acidity is important for control of vascular function. The mechanisms linking disturbed acid-base balance to changes in vascular tone have not been understood in detail.• We show that intracellular alkalinisation of endothelial cells in resistance arteries inhibits myoendothelial coupling and endothelium-dependent vasorelaxation. Although hyperpolarisations are generated in the endothelial cells under alkaline conditions, they are not transferred to the smooth muscle cells. Similarly, dye transfer between endothelial cells is inhibited during intracellular alkalinisation.• These results support the suggestion that intracellular pH is important for control of gap junction conductivity and intercellular communication. We describe a potential new molecular mechanism for development of vascular dysfunction in pathologies (e.g. diabetes, hypertension) involving altered myoendothelial signalling.Abstract Gap junctions mediate intercellular signalling in arteries and contribute to endothelium-dependent vasorelaxation, conducted vascular responses and vasomotion. Considering its putative role in vascular dysfunction, mechanistic insights regarding the control of gap junction conductivity are required. Here, we investigated the consequences of endothelial alkalinisation for gap junction communication and endothelium-dependent vasorelaxation in resistance arteries. We studied mesenteric arteries from NMRI mice by myography, confocal fluorescence microscopy and electrophysiological techniques. Removing CO 2 /HCO 3 − , reducing extracellular [Cl − ] or adding 4,4 -diisothiocyanatostilbene-2,2 -disulphonic acid inhibited or reversed Cl − /HCO 3 − exchange, alkalinised the endothelium by 0.2-0.3 pH units and inhibited acetylcholine-induced vasorelaxation. NO-synthase-dependent vasorelaxation was unaffected by endothelial alkalinisation whereas vasorelaxation dependent on small-and intermediate-conductance Ca 2+ -activated K + channels was attenuated by ∼75%. The difference in vasorelaxation between arteries with normal and elevated endothelial intracellular pH (pH i ) was abolished by the gap junction inhibitors 18β-glycyrrhetinic acid and carbenoxolone while other putative modulators of endothelium-derived hyperpolarisations -Ba 2+ , ouabain, iberiotoxin, 8Br-cAMP and polyethylene glycol catalase -had no effect. In the absence of CO 2 /HCO 3 − , addition of the Na acetylcholine were unaffected by omission of CO 2 /HCO 3 − . By contrast, dye transfer between endothelial cells and endothelium-derived hyperpolarisations of vascular smooth muscle cells stimulated by acetylcholine or the proteinase-activated receptor 2 agonist SLIGRL-amide were inhibited in the absence of CO 2 /HCO 3 − . We conclude that intracellular alkalinisation of endothelial cells attenu...

Human lymphatic vessel contractile activity is inhibited in vitro but not in vivo by the calcium channel blocker nifedipine

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Intracellular Acidification Alters Myogenic Responsiveness and Vasomotion of Mouse Middle Cerebral Arteries

“…2,4 In addition, acidification of endothelial cells in mesenteric arteries inhibits NO-synthase activity and NO-mediated vasorelaxation, 2,4 whereas endothelial cell alkalinization attenuates gap-junctiondependent intercellular coupling and endothelium-dependent hyperpolarizations. 7 These findings have established a fundamental role for pH i in modulating the vasomotor function of mesenteric arteries. In contrast, remarkably little is known about the regulation of pH i and its functional implications in other vascular beds, including cerebral arteries where NBCn1 is known to be expressed, 1,8 but its functional role for pH i regulation and vasomotor function requires further investigation.…”

The contribution of K+ channels to human thoracic duct contractility

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