SHORT-TERM REGULATION OF ENDOTHELIN RECEPTOR-MEDIATED PHOSPHOINOSITIDE HYDROLYSIS AND ARACHIDONIC-ACID RELEASE IN A7R5 SMOOTH-MUSCLE CELLS

In this study, the short-term regulation of endothelin-1- (ET-1) induced phosphoinositide (PI) hydrolysis and arachidonic acid release were investigated in cultured rat aortic smooth-muscle cells. ET-1, but not the ETB-selective peptide sarafotoxin (SFX) S6c, induced a dose-dependent increase in [H-3]inositol phosphate release (EC50 = 0.4 +/- 0.1 nM). ET-3 stimulated this response only at concentrations >0.1 muM. The ETA receptor antagonist BQ-123 inhibited ET-1-induced PI turnover, with an IC50 value of 97 +/- 15 nM. Pre-exposure of intact cells to ET-1 resulted in a 72% and 73% reduction in the ability of ET-1 or SFX S6b, respectively, to stimulate [H-3]inositol phosphate release, without affecting the response to vasopressin. In contrast, PI turnover induced by ET-1 or SFX S6b was only slightly lowered, by 28% and 22%, after a 30-min preincubation period with SFX S6b. ET-1, but not SFX S6c, also stimulated [H-3]arachidonic acid release by two-fold (EC50 = 3 +/- 0.8 nM). Pretreatment of intact cells with neomycin or phorbol-12-myristate-13-acetate resulted in a 49% and 44% inhibition of ET-1-induced [H-3]inositol phosphate accumulation but did not decrease ET-1-stimulated [H-3]arachidonic acid release, suggesting that these responses are separately regulated events in these cells.