Inhibition by nicardipine of endothelin-mediated inositol phosphate formation and Ca2+ mobilization in smooth muscle cell.
We have investigated the effects of endothelin on phosphoinositide metabolism and Ca2+ mobilization in cultured A10 cells. Endothelin stimulated a significant increase in inositol phosphate formation in a time- and dose-dependent manner. IP3 was significantly elevated by 30 sec and reached a 2.0-fold above control at 1 min. The EC50 for endothelin was 0.5 nM. The initiation of inositol phosphate formation was independent of extracellular Ca2+, and the Ca2+ ionophore, A23187, did not stimulate IP3 formation. However, the sustained elevation of inositol phosphates was partially inhibited by incubating cells in buffer lacking Ca2+ or in buffer containing nicardipine. Endothelin mobilized both intracellular and extracellular Ca2+ reaching a peak intracellular concentration of 350 +/- 11 nM by 1 min when cells were bathed with Ca2+-complete buffer. Intracellular Ca2+ remained 2-fold above baseline for at least 15 min. In contrast, when cells were exposed to endothelin in Ca2+-free buffer, the peak value of [Ca2+]i was 195 +/- 20 nM and returned to baseline by 2 min. Nicardipine completely blocked the influx of extracellular Ca2+ but did not interfere with the mobilization of intracellular stores. We conclude that endothelin produces a rapid and sustained elevation in inositol phosphate formation. The rapid production of IP3 is consistent with the time course for mobilization of intracellular Ca2+. Elevated cytosolic Ca2+ levels are maintained by the influx of extracellular Ca2+ through a nicardipine-sensitive Ca2+ channel and are involved in the sustained formation of inositol phosphates. These data provide an explanation for the sustained, nicardipine-inhibitable contraction of coronary artery strips induced by endothelin.
Xuan
Y T
YT
Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina 27710.
Whorton
A R
AR
Watkins
W D
WD
D000818:Animals; D001572:Benzofurans; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism*; D002460:Cell Line; D004095:Dihydropyridines; D016232:Endothelins; D004730:Endothelium, Vascular / Q000378:metabolism / Q000502:physiology*; D005456:Fluorescent Dyes; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism / Q000502:physiology*; D009529:Nicardipine / Q000494:pharmacology*; D010455:Peptides / Q000502:physiology*; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D013403:Sugar Phosphates / Q000037:antagonists & inhibitors*
D001572:Benzofurans; D015220:Calcium Channels; D004095:Dihydropyridines; D016232:Endothelins; D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D010455:Peptides; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D013403:Sugar Phosphates; C038806:1,4-dihydropyridine; D015544:Inositol 1,4,5-Trisphosphate; D009529:Nicardipine; D016257:Fura-2