We have found that human chymase produces a 31-amino acid endothelin [ET-1-(131)] from the 38-amino acid precursor (Big ET-1). We examined the mechanism of synthetic ET-1-(131)-induced intracellular Ca²⁺ signaling in cultured human coronary artery smooth muscle cells. ET-1-(131) increased the intracellular free Ca²⁺ concentration ([Ca²⁺]_i) in a concentration-dependent manner (10¹⁴-10¹⁰ M). This ET-1-(131)-induced [Ca²⁺]_i increase was not affected by phosphoramidon, Bowman-Birk inhibitor, and thiorphan. The ET-1-(131)-induced [Ca²⁺]_i increase was not influenced by removal of extracellular Ca²⁺ but was inhibited by thapsigargin. ET-1-(131) at 10¹² M did not cause Ca²⁺ influx, whereas 10⁷ M ET-1-(131) evoked marked Ca²⁺ influx, which was inhibited by nifedipine. ET-1-(131) also increased inositol trisphosphate formation. These results suggest that the ET-1-(131)-induced [Ca²⁺]_i increase at relatively low concentrations is attributable to the release of Ca²⁺ from inositol trisphosphate-sensitive intracellular stores, whereas Ca²⁺ influx into the cells evoked by high concentration of ET-1-(131) probably occurs through voltage-dependent Ca²⁺ channels. We concluded that the physiological activity of ET-1-(131) may be attributable to Ca²⁺ mobilization from intracellular stores rather than influx of Ca²⁺ from extracellular space.

human chymase; confocal laser microscopy

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