EFFECTS OF THROMBIN RECEPTOR ACTIVATING PEPTIDE ON PHOSPHOINOSITIDE HYDROLYSIS AND PROTEIN-KINASE-C ACTIVATION IN CULTURED RAT AORTIC SMOOTH-MUSCLE CELLS - EVIDENCE FOR TETHERED-LIGAND ACTIVATION OF SMOOTH-MUSCLE CELL THROMBIN RECEPTORS

Phosphoinositide hydrolysis and protein kinase C (PKC) activation were examined in response to treatment of rat aortic smooth muscle cells with alpha-thrombin and a seven amino acid thrombin receptor activating peptide (TRAP-7; SFLLRNP). Alpha-thrombin and TRAP-7 stimulated total inositol phosphate (IP) accumulation and phosphorylation of a specific endogenous substrate for activated PKC. Acetylated TRAP-7 and ''reverse'' TRAP (FSLLRNPNDKYEPF) were ineffective in stimulating signal transduction. The active site inhibitor, MD805 (argatroban), and the anion-binding exosite inhibitor, BMS 180,742, reduced the IP response to alpha-thrombin in a concentration-dependent manner. In contrast, the TRAP-7-induced IP response was not affected by either inhibitor. These data are consistent with the tethered-ligand hypothesis for thrombin receptor activation in rat aortic smooth muscle cells.