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 c ouple to both the adenosine 3',5'-cyclic monophosphate and inositol 1, 4,5-trisphosphate/intracellular Ca2+ signaling pathways in a stimulato ry manner. We undertook the present studies to further characterize th e postreceptor events involved in H-2 receptor dual signaling. Histami ne H-2 receptor-mediated signal transduction was examined in isolated cell membranes prepared from purified canine parietal cells and HEPA c ells (rat hepatoma cell line) stably transfected to express the canine H-2 histamine receptor cDNA. Histamine dose-dependently:stimulated bo th 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) a ctivity in an H-2-specific and GTP-dependent manner. Cholera toxin pre treatment abolished the stimulatory effect of histamine on PLC activit y in isolated membranes without altering binding of the H-2 receptor a ntagonist tiotidine. Anti-G(s) alpha dose-dependently inhibited histam ine-stimulated AC activity while leaving the effect of this secretagog ue on PLC activity unaltered. Although anti-G(q) alpha inhibited vasop ressin-stimulated PLC activity in HEPA cells and carbachol-stimulated PLC in parietal cells, this antibody did not alter the action of hista mine on PLC in the same membrane preparations. Antibody against the NH 2 and COOH terminals of the common beta-subunit of heterotrimeric G pr oteins did not inhibit histamine-stimulated PLC activity. Our studies demonstrate for the first time that activation of the H-2 receptor lea ds to stimulation of both AC and PLC via separate GTP-dependent mechan isms.