Role of nonselective cation channels as Ca 2+ entry pathway in endothelin-1-induced contraction and their suppression by nitric oxide

Abstract

The present study was carried out to clarify the role of nonselective cation channels as a Ca 2+ entry pathway in the contraction and the increase in [Ca 2+] i induced by endothelin-1 in endothelium-denuded rat thoracic aorta rings, and their suppression by nitric oxide (NO). In Ca 2+-free medium, the endothelin-1-induced contraction was suppressed to about 20% of control values, although the increase in [Ca 2+] i became negligible. The contraction and the increase in [Ca 2+] i monitored by fura 2 fluorescence were unaffected by a blocker of L-type voltage-operated Ca 2+ channels nifedipine. A blocker of nonselective cation channels 1-[ β-[3-(4-methoxyphenyl)propoxyl]-4-methoxyphenethyl]-1 H-imidazole·HCl(SK&F 96365) suppressed the endothelin-1-induced contraction and increase in [Ca 2+] i to the level similar to that after removal of extracellular Ca 2+. SK&F 96365 had no further effect on the endothelin-1-induced contraction in the absence of extracellular Ca 2+. The endothelin-1-induced contraction and increase in [Ca 2+] i were abolished by a donor of NO sodium nitroprusside. The effects of another NO donor 3-morpholinosydnonimine (SIN-1) were also tested and yielded essentially similar results to those for sodium nitroprusside on the endothelin-1-induced contraction. Furthermore, the inhibitory effects of sodium nitroprusside could be blocked with a guanylate cyclase inhibitor 1 H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ) at 30 μM. These findings suggest that Ca 2+ entry through nonselective cation channels but not voltage-operated Ca 2+ channels plays a critical role in the endothelin-1-induced increase in [Ca 2+] i and the resulting contraction and that inhibition by NO of the endothelin-1-induced contraction is mainly the result of blockade of Ca 2+ entry through these channels.