Enhancement by baclofen of the Gs-coupled receptor-mediated cAMP production in Xenopus oocytes expressing rat brain cortex poly (A)+ RNA: a role of G-protein beta gamma subunits.
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.
Uezono
Y
Y
Department of Pharmacology, University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan. uezonoy@med.uoeh-u.ac.jp
Ueda
Y
Y
Ueno
S
S
Shibuya
I
I
Yanagihara
N
N
Toyohira
Y
Y
Yamashita
H
H
Izumi
F
F
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism; D004594:Electrophysiology; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D017930:Genes, Reporter; D007545:Isoproterenol / Q000494:pharmacology; D009865:Oocytes; D012333:RNA, Messenger; D051381:Rats; D018080:Receptors, GABA-B / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology; D014981:Xenopus
D000318:Adrenergic beta-Agonists; D018755:GABA Agonists; D018756:GABA Antagonists; D012333:RNA, Messenger; D018080:Receptors, GABA-B; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D014660:Vasoactive Intestinal Peptide; D000242:Cyclic AMP; D019205:GTP-Binding Protein alpha Subunits, Gs; D001418:Baclofen; D007545:Isoproterenol; C057491:2-hydroxysaclofen