Functional coupling between A1 adenosine receptors and G-proteins in rat hippocampal membranes assessed by high-affinity GTPase activity.
1. In order to investigate the functional interaction between adenosine receptors and G-proteins in native brain membranes, stimulation of high-affinity GTPase activity by adenosine receptor agonists was characterized in rat hippocampal membranes. 2. Addition of 1 microM R-N6-phenylisopropyladenosine (R-PIA), a selective A1 adenosine receptor agonist, augmented the Vmax of the low-KM GTPase by 51%, with a slight increase in the KM value. 3. Several adenosine receptor agonists stimulated the high-affinity GTPase activity in a concentration-dependent manner, with a rank order of potency indicative of the involvement of A1 adenosine receptor subtype as follows: R-PIA > N6-cyclohexyladenosine > 5'-N-ethylcarboxamidoadenosine > or = 2-chloroadenosine > S-PIA > CGS 21680, 2-phenylaminoadenosine. 4. The selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine, inhibited R-PIA-stimulated high-affinity GTPase activity in a competitive manner, with a KB value of 2.5 nM. 5. The activating effects on high-affinity GTPase of R-PIA (via A1 adenosine receptors) and of 5-HT (via 5-HT1A receptors) were completely additive, indicating that A1 adenosine and 5-HT1A receptors were coupled to distinct pools of G-proteins in hippocampus. 6. Stimulation of high-affinity GTPase activity by adenosine receptor agonists can be used as a valuable measure for the investigation of the functional coupling between A1 adenosine receptors and G-proteins associated with adenylyl cyclase inhibition.
Odagaki
Y
Y
Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
Fuxe
K
K
D000818:Animals; D001667:Binding, Competitive; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006624:Hippocampus / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000201:enzymology / Q000378:metabolism / Q000648:ultrastructure; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D010761:Phosphorus Radioisotopes; D058906:Purinergic P1 Receptor Agonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology; D013268:Stimulation, Chemical; D014970:Xanthines / Q000494:pharmacology
D004791:Enzyme Inhibitors; D010761:Phosphorus Radioisotopes; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1; D011985:Receptors, Serotonin; D014970:Xanthines; D010660:Phenylisopropyladenosine; D012701:Serotonin; C051360:1,3-dipropyl-8-cyclopentylxanthine; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins