| Abstract: | Pertussis toxin, PT, abolishes inhibitory regulation of adenylate cyclase by cell surface receptors. Inhibitors of adenylate cyclase in GH3 cells, namely somatostatin and the muscarinic cholinergic agonist carbachol, lower the cytosolic free Ca2+ concentration. Ca2+]i and cause hyperpolarization. These responses are selectively abolished by PT. It is concluded that the effects of somatostatin and carbachol to lower Ca2+]i and to hyperpolarize are secondary to their inhibitory action on adenylate cyclase. In contrast, PT does not impair the TRH induced rise in Ca2+]i in GH3 cells demonstrating that the coupling of TRH receptors to Ca2+ mobilization is not mediated by a PT substrate. |
