Comparison of the effects of endothelin-1,-2 and-3 (1-31) on changes in [Ca2+](i) in human coronary artery smooth muscle cells

We have previously found that human chymase selectively cleaves big endothe lins (ETs) at the Tyr(31)-Gly(32) bond to produce 31-amino-acid endothelins , ETs (1-31). In the present study, we investigated the effects of ETs (1-3 1) on changes in intracellular free Ca2+ ([Ca2+](i)) in cultured human coro nary artery smooth muscle cells (HCASMCs) using confocal laser microscopy. ETs (1-31) increased [Ca2+](i) in a concentration-dependent manner. Phospho ramidon did not inhibit the increases in [Ca2+](i) caused by ETs (1-31). Th e [Ca2+](i) increases induced by ETs (1-31) were compared to those of ETs ( 1-21) and big ETs. ET-1 (1-21)was about 10-times more potent than big ET-1 or ET-1 (1-31), whereas big ET-2 was 10-times less potent than ET-2 (1-21) or ET-2 (1-31). ETs (1-31) may induce [Ca2+](i) increase through ETA-type o r ETA-type-like receptors. The 10(-12) M ET (1-31)-induced increases in [Ca 2+](i) were not affected by removal of extracellular Ca2+, but were inhibit ed by thapsigargin. These results suggested that ET-1, -2 and -3 (1-31) sho wed similar potencies in increasing [Ca2+](i) and mechanisms of ET (1-31)-i nduced increases in [Ca2+](i) may be similar among the three ETs (1-31).