Intercellular calcium signaling and nitric oxide feedback during constriction of rabbit renal afferent arterioles

Vasoconstriction and increase in the intracellular calcium concentration ([Ca2+]i) of vascular smooth muscle cells may cause an increase of endothelial cell [Ca2+]i, which, in turn, augments nitric oxide (NO) production and inhibits smooth muscle cell contraction. This hypothesis was tested in microperfused rabbit renal afferent arterioles, using fluorescence imaging microscopy with the calcium-sensitive dye fura-2 and the NO-sensitive dye 4-amino-5-methylamino-2′,7′- difluorescein. Both dyes were loaded into smooth muscle and endothelium. Depolarization with 100 mmol/l KCl led to a transient vasoconstriction which was converted into a sustained response by N-nitro-L-arginine methyl ester (L-NAME). Depolarization increased smooth muscle cell [Ca2+] i from 162 ± 15 nmol/l to a peak of 555 ± 70 nmol/l (n = 7), and this response was inhibited by 80% by the L-type calcium channel blocker calciseptine. After a delay of 10 s, [Ca2+]i increased in endothelial cells immediately adjacent to reactive smooth muscle cells, and this calcium wave spread in a nonregenerative fashion laterally into the endothelial cell layer with a velocity of 1.2 μm/s. Depolarization with 100 mmol/l KCl led to a significant increase in NO production ([NO]i) which was inhibited by L-NAME (n = 5). Acetylcholine caused a rapid increase in endothelial [Ca2+]i, which did not transfer to the smooth muscle cells. L-NAME treatment did not affect changes in smooth muscle [Ca 2+]i after depolarization, but it did increase the calcium sensitivity of the contractile apparatus. We conclude that depolarization increases smooth muscle [Ca2+]i which is transferred to the endothelial cells and stimulates NO production which curtails vasoconstriction by reducing the calcium sensitivity of the contractile apparatus. Copyright © 2007 the American Physiological Society.link_to_subscribed_fulltex