Comparison of the Effects of Endothelin-1, -2 and -3 (1 - 31) on Changes in [Ca²⁺]_i in Human Coronary Artery Smooth Muscle Cells

Abstract

We have previously found that human chymase selectively cleaves big endothelins (ETs) at the Tyr³¹-Gly³² bond to produce 31-amino-acid endothelins, ETs (1 - 31). In the present study, we investigated the effects of ETs (1 - 31) on changes in intracellular free Ca²⁺ ([Ca²⁺]_i) in cultured human coronary artery smooth muscle cells (HCASMCs) using confocal laser microscopy. ETs (1 - 31) increased [Ca²⁺]_i in a concentration-dependent manner. Phosphoramidon did not inhibit the increases in [Ca²⁺]_i caused by ETs (1 - 31). The [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 ET_A-type or ET_A-type-like receptors. The 10^-12 M ET (1 - 31)-induced increases in [Ca²⁺]_i were not affected by removal of extracellular Ca²⁺, but were inhibited by thapsigargin. These results suggested that ET-1, -2 and -3 (1 - 31) showed similar potencies in increasing [Ca²⁺]_i and mechanisms of ET (1 - 31)-induced increases in [Ca²⁺]_i may be similar among the three ETs (1 - 31).