Histamine H-2 receptor activates adenylate cyclase and PLC via separate GTP-dependent pathways

Previously, we demonstrated that a single histamine H-2 receptor can couple to both the adenosine 3',5'-cyclic monophosphate and inositol 1,4,5-trisphosphate/intracellular Ca2+ signaling pathways in a stimulatory manner. We undertook the present studies to further characterize the postreceptor events involved in H-2 receptor dual signaling. Histamine H-2 receptor-mediated signal transduction was examined in isolated cell membranes prepared from purified canine parietal cells and HEPA cells (rat hepatoma cell line) stably transfected to express the canine H-2 histamine receptor cDNA. Histamine dose-dependently:stimulated both adenylate cyclase [AC; mean effective concentration (EC(50)) = 2 X 10(-7) M] and phospholipase C (PLC; EC(50) = 3.1 +/- 0.5 X 10(-7) M) activity in an H-2-specific and GTP-dependent manner. Cholera toxin pretreatment abolished the stimulatory effect of histamine on PLC activity in isolated membranes without altering binding of the H-2 receptor antagonist tiotidine. Anti-G(s) alpha dose-dependently inhibited histamine-stimulated AC activity while leaving the effect of this secretagogue on PLC activity unaltered. Although anti-G(q) alpha inhibited vasopressin-stimulated PLC activity in HEPA cells and carbachol-stimulated PLC in parietal cells, this antibody did not alter the action of histamine on PLC in the same membrane preparations. Antibody against the NH2 and COOH terminals of the common beta-subunit of heterotrimeric G proteins did not inhibit histamine-stimulated PLC activity. Our studies demonstrate for the first time that activation of the H-2 receptor leads to stimulation of both AC and PLC via separate GTP-dependent mechanisms.