Pertussis toxin inhibits thrombin-induced activation of phosphoinositide hydrolysis and Na+/H+ exchange in hamster fibroblasts

Abstract

Prior treatment with pertussis toxin of G0-arrested hamster fibroblasts (CCL39) results in a dose-dependent inhibition of two early events of the mitogenic response elicited by alpha-thrombin: accumulation of inositol phosphates in Li+-treated cells, and activation of the Na+/H+ antiport, measured either by the amiloride-sensitive 22Na+ influx or by the increase in intracellular pH. At 10(-1) U/ml of alpha-thrombin, the maximal inhibition was approximately 50% for these two early cellular responses, but the pertussis toxin effect was more pronounced at lower thrombin concentrations. In contrast, pertussis toxin does not affect the Na+/H+ antiport activation induced by phorbol esters or EGF, the action of which is not mediated by the phosphoinositide-metabolizing pathway in CCL39 cells. Therefore, our data suggest the following. A GTP-binding regulatory protein is probably involved in signal transduction between thrombin receptors and the phosphatidylinositol 4,5-bisphosphate-specific phospholipase C. This regulation does not seem to be exerted via modulations of cyclic AMP levels. The thrombin-induced activation of Na+/H+ antiport is, at least in part, mediated by the protein kinase C, as a consequence of stimulation of phosphatidylinositol turnover.