title: Adenosine A1 agonists and the Ca2+ channel agonist bay K 8644 produce a synergistic stimulation of the GTPase activity of Go in rat frontal cortical membranes.
abstract: The identity and role of G proteins in coupling adenosine receptors to effectors have been studied to a limited degree. We have identified the G proteins whose GTPase activity is stimulated by adenosine receptor agonists in neuronal membranes. (R)-Phenylisopropyladenosine, 2-chloroadenosine, and N-ethylcarboxamideadenosine produced a concentration-dependent stimulation of GTPase. At 10(-5) M, the increase above basal GTPase in frontal cortex was 25 +/- 4, 20 +/- 3, and 8 +/- 1%, respectively, and in the cerebellum 55 +/- 2, 41 +/- 4, and 22 +/- 2%, respectively. The effects of (R)-phenylisopropyladenosine and 2-chloroadenosine were inhibited by (1) A1 antagonists (76-96% reduction), (2) pretreatment with pertussis toxin (90-100% reduction), and (3) antibodies raised against the alpha-subunit of Gi and G(o) (55-57% reduction by each), suggesting that A1 receptors interact equally with Gi and G(o). (R)-Phenylisopropyladenosine increased the binding of a nonhydrolyzable analogue of GTP to membranes in a pertussis toxin-sensitive manner, indicative of activation of Gi or G(o). Previously, (+/-)-Bay K 8644 enhanced GTP hydrolysis by G(o) but not Gi. Now we report a profound synergistic stimulation of GTPase in the presence of (R)-phenylisopropyladenosine and (+/-)-Bay K 8644 (10(-7) to 10(-5) M). (+/-)-Bay K 8644 had no effect on nucleotide exchange and, thus, cannot activate G(o). It appears that a positive cooperative stimulation of G(o) occurs when it is first activated by A1 receptors and subsequently interacts with the L-type Ca2+ channel.
authors.affiliation: Department of Pharmacology, Royal Free Hospital School of Medicine, London, England.
authors.forename: M I
authors.initials: MI
authors.lastname: Sweeney
authors.forename: A C
authors.initials: AC
authors.lastname: Dolphin
mesh_terms: D015762:2-Chloroadenosine / Q000494:pharmacology; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide); D000595:Amino Acid Sequence; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D004357:Drug Synergism; D005625:Frontal Lobe / Q000201:enzymology*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D037342:Pertussis Toxin; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D058906:Purinergic P1 Receptor Agonists; D051381:Rats; D017208:Rats, Wistar; D018047:Receptors, Purinergic P1 / Q000502:physiology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1; D010566:Virulence Factors, Bordetella; D015762:2-Chloroadenosine; D010660:Phenylisopropyladenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D000241:Adenosine