ENHANCEMENT BY BACLOFEN OF THE GS-COUPLED RECEPTOR-MEDIATED CAMP PRODUCTION IN XENOPUS OOCYTES EXPRESSING RAT-BRAIN CORTEX POLY (A)(- A ROLE OF G-PROTEIN BETA-GAMMA-SUBUNITS() RNA )

We investigated the mechanism by which GABA-B receptors enhance the Gs -coupled receptor-mediated cAMP production in Xenopus oocytes expressi ng poly (A)(+) RNA derived from rat brain cortex. We expressed the cys tic fibrosis transmembrane conductance regulator gene (CFTR) as a repo rter for cAMP changes in oocytes. The GABA-B agonist (-)baclofen enhan ced the adrenergic beta(2) agonist isoproterenol- or vasoactive intest inal peptide (VIP)-induced CFTR currents, whereas (-)baclofen alone di d not cause any currents. The (-)baclofen-enhanced currents were inhib ited by the GABA-B antagonist 2-OH saclofen. The enhancement by (-)bac lofen was further augmented by coexpressing adenylyl cyclase (AC) type II, an isotype activated by G beta gamma and G alpha s, but not by co expressing AC type III, an isotype insensitive to G beta gamma. Moreov er, pretreatment of the oocytes with pertussis toxin (PTX) abolished t he enhanced effect of(-)baclofen. These results indicate that upon GAB A-B activation, the G beta gamma released from PTX-sensitive G-protein s activates the AC type Il (or IV), and this process requires the G al pha s activation by Gs-coupled receptors. (C) 1997 Academic Press.