Beta gamma-mediated enhancement of corticotropin-releasing hormone-stimulated adenylyl cyclase activity by activation of gamma-aminobutyric acid(B) receptors in membranes of rat frontal cortex.
A number of studies have shown that activation of gamma-aminobutyric acid(B) (GABA(B)) receptors potentiates neurotransmitter-induced accumulation of cyclic AMP in brain slices, but the mechanisms involved in the facilitatory effect have not been fully elucidated. In the present study, we showed that in membranes of rat frontal cortex the GABA(B) receptor agonist (-)baclofen increased basal adenylyl cyclase activity and potentiated the maximal enzyme stimulation elicited by corticotropin-releasing hormone (CRH). The less active enantiomer (+)baclofen had no effect on cyclic AMP formation, whereas the natural agonist GABA mimicked the stimulatory action of (-)baclofen. In radioligand-binding experiments, the affinity and maximal binding capacity of (125)I-Tyr-CRH was not affected by (-)baclofen. The GABA(B) receptor antagonist CGP 55845A competitively counteracted the (-)baclofen potentiation of CRH-stimulated adenylyl cyclase activity with a pA(2) value of 6.70. Moreover, both (-)baclofen and GABA, but not (+)baclofen, caused a concentration-dependent stimulation of [(35)S]GTP gamma S binding to membrane G-proteins. The intracerebral injection of pertussis toxin significantly reduced the facilitatory effects of (-)baclofen on both basal and CRH-stimulated adenylyl cyclase activities. Moreover, membrane incubation with the GDP-bound form of the alpha subunit of transducin, a scavenger of G protein beta gamma subunits, blocked the stimulatory effects of (-)baclofen. The data indicate that in rat frontal cortex activation of GABA(B) receptors potentiates the CRH stimulation of adenylyl cyclase activity through a mechanism involving the beta gamma subunits of the pertussis toxin-sensitive G protein G(i)/G(o).
Onali
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Section of Biochemical Pharmacology, Department of Neuroscience, University of Cagliari, 09124 Cagliari, Italy. onali@unica.it
Olianas
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D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D018756:GABA Antagonists / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008297:Male; D037342:Pertussis Toxin; D010721:Phosphinic Acids / Q000494:pharmacology; D017397:Prefrontal Cortex / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018080:Receptors, GABA-B / Q000378:metabolism*; D013462:Sulfur Radioisotopes; D015293:Transducin / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D018756:GABA Antagonists; D007457:Iodine Radioisotopes; D010721:Phosphinic Acids; D011412:Propanolamines; D018080:Receptors, GABA-B; D013462:Sulfur Radioisotopes; D010566:Virulence Factors, Bordetella; C085075:CGP 55845A; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D003346:Corticotropin-Releasing Hormone; D037342:Pertussis Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin; D000262:Adenylyl Cyclases