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1Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra; 2Department of Physiology and Pharmacology, School of Medical Sciences, University of New South Wales, Sydney; and 3Department of Anatomy and Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, Australia
Submitted 11 May 2006 ; accepted in final form 26 June 2006
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 (SMCs), and these preceded rhythmical contractions during which adjacent SMC intracellular calcium concentration ([Ca2+]i) waves were synchronized. Endothelium 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 dibutyryl 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) composed of connexins 37 and 40 connected the endothelial cell and SMC layers. Synchronized vasomotion in rat basilar artery is endothelium dependent, with [Ca2+]i waves generated within SMCs being coordinated by electrical coupling via myoendothelial gap junctions.
connexin; electron microscopy; endothelial function; potassium channel; membrane potential
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