Endothelin receptor is coupled to phospholipase C via a pertussis toxin-insensitive guanine nucleotide-binding regulatory protein in vascular smooth muscle cells

The mechanisms of endothelin-1 (ET) actions were investigated in cultured rat aortic vascular smooth muscle A-10 cells. The A-10 cells have a single class of high affinity binding sites for ET with an apparent M_r of 65,000-75,000 on SDS-PAGE. Stimulation of cells with ET induces mobilization of Ca²⁺ from both intra- and extracellular pools to produce a bip basic increase in cytoplasmic free Ca²⁺ concentration. ET increases cellular levels of inositol trisphosphate and 1,2-diacylglycerol, indicating activation of phospholipase C by ET. ET stimulates production of inositol phosphates in membranes prepared from A-10 cells in the presence of guanosine 5′-O-(thiotriphosphate) (GTPγS), but not in its absence. Further, specific binding of ¹²⁵I-labeled ET to A-10 cell membranes is shown to be inhibited by GTPγS in a dose-dependent manner. Treatment of A-10 cells with pertussis toxin induces ADP-ribosylation of a 41,000-D membrane protein but fails to block the ET-induced increases in inositol phosphate production and Ca²⁺ mobilization. These results indicate that the receptor for ET is coupled to phospholipase C via a guanine nucleotide-binding regulatory protein which is distinct from the pertussis toxin substrate in A-10 cells.