vasoactive-intestinal-peptide and 2-hydroxysaclofen

We investigated the mechanism by which GABA-B receptors enhance the Gs-coupled receptor-mediated cAMP production in Xenopus oocytes expressing poly (A)+ RNA derived from rat brain cortex. We expressed the cystic fibrosis transmembrane conductance regulator gene (CFTR) as a reporter for cAMP changes in oocytes. The GABA-B agonist (-)baclofen enhanced the adrenergic beta 2 agonist isoproterenol- or vasoactive intestinal peptide (VIP)-induced CFTR currents, whereas (-)baclofen alone did not cause any currents. The (-)baclofen-enhanced currents were inhibited by the GABA-B antagonist 2-OH saclofen. The enhancement by (-)baclofen was further augmented by coexpressing adenylyl cyclase (AC) type II, an isotype activated by G beta gamma and G alpha s, but not by coexpressing AC type III, an isotype insensitive to G beta gamma. Moreover, pretreatment of the oocytes with pertussis toxin (PTX) abolished the enhanced effect of (-)baclofen. These results indicate that upon GABA-B activation, the G beta gamma released from PTX-sensitive G-proteins activates the AC type II (or IV), and this process requires the G alpha s activation by Gs-coupled receptors.

Topics: Adrenergic beta-Agonists; Animals; Baclofen; Cerebral Cortex; Cyclic AMP; Cystic Fibrosis Transmembrane Conductance Regulator; Electrophysiology; GABA Agonists; GABA Antagonists; Genes, Reporter; GTP-Binding Protein alpha Subunits, Gs; Isoproterenol; Oocytes; Rats; Receptors, GABA-B; RNA, Messenger; Vasoactive Intestinal Peptide; Xenopus