Involvement of the βγ subunits of G proteins in the cAMP response induced by stimulation of the histamine H1 receptor

Stimulation of the histamine H1 receptor has been shown to enhance adenosine 3′, 5′-cyclic monophosphate (cAMP) accumulation in various cell types but, to date, the mechanism by which this occurs is still unclear. In the present study, we examined the possibility that the βγ subunits of G proteins (Gβγ) are involved in this process in cultured Chinese hamster ovary cells transfected with the human histamine H1 receptor (CHO-H1). Histamine increased intracellular cAMP levels in a concentration-dependent manner in CHO-H1 cells, and this histamine action was abolished by pyrilamine (1 μM). Inhibition of histamine H1 receptor-Gq protein coupling by stable expression of the C-terminal peptide of Gαq protein significantly attenuated the cAMP accumulation induced by histamine. By comparison, neither BAPTA/AM (50 μM), an intracellular Ca2+ chelator, nor GF 109203X (1 μM), an inhibitor of protein kinase C, influenced the cAMP response. Histamine H1 receptor-mediated cAMP accumulation was significantly inhibited by transient transfection of CHO-H1 cells with the C-terminal peptide of β-adrenoceptor kinase I (residues 542–685), a scavenger of Gβγ. Stable expression of the C-terminal peptide of the Gαs protein, but not treatment with pertussis toxin (200 ng/ml for 24 h), attenuated the histamine H1 receptor-mediated cAMP accumulation. These results suggest that stimulation of histamine H1 receptors activates adenylyl cyclase through the release of Gβγ subunits from G proteins, thereby elevating intracellular cAMP levels.