Evidence for a contribution of store-operated Ca2+ channels to NO-mediatedendothelium-dependent relaxation of guinea-pig aorta in response to a Ca2+ionophore, A23187

A23187 (6S-[6 alpha,8 beta,9 beta,11 alpha]-5-(methylamino)2-[3,9,11-trimet hyl-8-[1-methyl-2-oxo-2-(1H-pyrrol-2-yl)ethyl]-1,7-dioxaspiro[5.5] undec-2- yl] methyl]-4-benzoxazolecarboxylic acid, calcimycin), an antibiotic Ca2+ i onophore, produces an endothelium-dependent vascular relaxation. in the pre sent study, pharmacological features were functionally characterized of end othelium-dependent relaxant response of guinea-pig aorta to A23187, especia lly focusing on the possible Ca2+ source and Ca2+ mobilization mechanisms i n endothelial cells responsible for the vasorelaxant response to the Ca2+ i onophore. A23187-induced endothelium-dependent relaxation was suppressed pr ofoundly by N-G-nitro-L-arginine (L-NNA; 3 x 10(-4) M) or calmidazolium (3 x 10(-5) M), suggesting that nitric oxide (NO) produced by the enhanced act ivation of Ca2+/calmodulin-dependent endothelial NO synthase (eNOS) is larg ely responsible for the relaxant response of this artery to A23187. In the Ca2+-free solution without EGTA, NO-mediated endothelium-dependent relaxati on induced by A23187 was almost abolished, which suggests that Ca2+ entry f rom extracellular space into endothelial cells plays the key role in the A2 3187-induced functional vasorelaxation. On the other hand, SK&F96365 (1-[be ta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole; 5 x 10(-5 ) M) and Ni2+ (3 x 10(-4) M), both of which inhibit capacitative Ca2+ influ x through store-operated Ca2+ channels (SOCCs), attenuated significantly NO -mediated endo thelium-dependent relaxation by A23187. Furthermore, A23187- induced endothelium-dependent relaxation was suppressed more strongly than endothelium-independent relaxation induced by SIN-1 (3-morpholino-sydnonimi ne), an NO donor, when aortic preparation was preconstricted with high KCl instead of agonistic stimulation (prostaglandin F(2)alpha). These findings suggest that NO-mediated endothelium-dependent relaxant response of guinea- pig aorta to A23187 is preceded by the increase in endothelial cytosolic fr ee Ca2+ concentration ([Ca2+](cyt)) due to the enhanced Ca2+ influx from ex tracellular space. In the enhanced Ca2+ entry leading to the stimulation of eNOS and NO-mediated functional relaxant response of guinea-pig aorta to A 23187, activation of SOCCs but not the Ca2+ entry through plasma membrane C a2+-specific routes made by A23187 seems to play the predominant role. It i s most likely that A23187 acts primarily at the Ca2+ store sites in endothe lial cells, which subsequently depletes stored Ca2+ to activate SOCCs via u nidentified mechanisms.