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1 Physiology and Pharmacology, University of New South Wales, Sydney, New South Wales, Australia; JCSMR, Australian National University, Canberra, Australian Capital Territory, Australia
2 JCSMR, Australian National University, Canberra, Australian Capital Territory, Australia
3 Anatomy and Cell Biology, University of Melbourne, Melbourne, Victoria, Australia
4 Physiology and Pharmacology, University of New South Wales, Sydney, New South Wales, Australia
* To whom correspondence should be addressed. E-mail: caryl.hill{at}anu.edu.au.
Control of cerebral vasculature differs from that of systemic vessels outside the blood-brain barrier. The hypothesis that the endothelium modulates vasomotion via direct myoendothelial coupling was investigated in a small vessel of the cerebral circulation. In the primary branch of the rat basilar artery, membrane potential, diameter, and calcium dynamics associated with vasomotion were examined using selective inhibitors of endothelial function in intact and endothelium-denuded arteries. Vessel anatomy, protein and mRNA expression were studied using conventional electron microscopy high resolution ultrastructural and confocal immunohistochemistry and quantitative PCR. Membrane potential oscillations were present in both endothelial cells and smooth muscle cells and these preceded rhythmical contractions during which adjacent SMC intracellular calcium ([Ca2+]i) waves were synchronized. Endothelial removal abolished vasomotion and desynchronized adjacent smooth muscle cell [Ca2+]i waves. NG-nitro-L-arginine methyl ester (10 µM) did not mimic this effect and db-cGMP (300 µM) failed to resynchronize [Ca2+]i waves in endothelium-denuded arteries. Combined charybdotoxin and apamin abolished vasomotion and depolarized and constricted vessels, even in absence of endothelium. Separately, 37,43Gap27 and 40Gap27 abolished vasomotion. Extensive myoendothelial gap junctions (3 per endothelial cell) comprised of connexins 37 and 40 connected the endothelial cell and smooth muscle cell layers. Synchronised vasomotion in rat basilar artery is endothelium-dependent, with [Ca2+]i waves generated within smooth muscle cells being coordinated by electrical coupling via myoendothelial gap junctions.
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