Endothelin generating pathway through endothelin 1–31 in human cultured bronchial smooth muscle cells

The effects of endothelin (ET)‐1 1–31 and ET‐2 1–31 , human chymase products of the corresponding big ETs, on the intracellular free Ca 2+ concentration ([Ca 2+ ] i ) and [ 125 I]‐ET‐1 binding were investigated using human cultured bronchial smooth muscle cells (BSMC). ET‐1 1–31 (10 −8 M – 3×10 −7 M ) and ET‐2 1–31 (3×10 −8 M –3×10 −6 M ) caused an increase in [Ca 2+ ] i in a concentration‐dependent manner. Big ET‐1 (3×10 −8 M – 10 −6 M ) also caused this increase, but not big ET‐2 at concentrations up to 10 −6 M . The [Ca 2+ ] i increase induced by ET‐1 was inhibited by both BQ123, an ET A ‐receptor antagonist, and BQ788, an ET B ‐receptor antagonist, whereas that induced by ET‐3 was inhibited by BQ788 but not by BQ123. Increases in [Ca 2+ ] i caused by ET‐1 1–31 , big ET‐1 and ET‐2 1–31 were completely inhibited by 10 −4 M phosphoramidon, a dual neutral endopeptidase (NEP)/endothelin‐converting enzyme (ECE) inhibitor, and 10 −5 M thiorphan, a NEP inhibitor. Scatchard plot analyses of the saturation curves of [ 125 I]‐ET‐1 and [ 125 I]‐ET‐3 showed that both ET A ‐ and ET B ‐ receptors at the ratio of 4 : 1 were expressed on BSMC. ET‐1 1–31 , big ET‐1 and ET‐2 1–31 inhibited [ 125 I]‐ET‐1 binding in a concentration‐dependent manner, and these effects were attenuated by treatment with thiorphan. On the other hand, big ET‐2 slightly inhibited the binding at a high concentration and this was not affected by thiorphan. These results suggest that ET‐1 1–31 , big ET‐1 and ET‐2 1–31 cause an increase in [Ca 2+ ] i by being converted into the corresponding ET‐1 and ET‐2 by NEP, but this did not occur with big ET‐2 in human BSMC. ET‐2 1–31 produced by human chymase from big ET‐2 might be important for the generation of ET‐2 in human bronchial tissue.British Journal of Pharmacology (1999) 127 , 1415–1421; doi: 10.1038/sj.bjp.0702664