Coupling of inhibitory receptors with Gi-proteins in hamster adipocytes: comparison between adenosine A1 receptor and alpha 2-adrenoceptor.
Adenosine A1 receptors and alpha 2-adrenoceptors are both potent inhibitors of adipocyte lipolysis when activated by their agonists. The aim of this work was to compare the coupling of these receptors to the Gi-proteins in hamster adipocytes. The adenosine A1 receptor was characterized with the antagonist [3H]dipropyl-cyclopentyl-xanthine ([3H]DPCPX) and the agonist [3H](-)-phenylisopropyladenosine ([3H]PIA). It was demonstrated by [32P]ADP-ribosylation with pertussis toxin and immunoblotting that Gi1, Gi2 and Gi3 are expressed in hamster adipocytes. Partial ADP-ribosylation of Gi-proteins by pertussis toxin, acting on the intact cells or on the adipocyte membranes, demonstrated that the adenosine A1 receptor was less sensitive to the disappearance of functional Gi-proteins than the alpha 2-adrenoceptor. These results are in accordance with the weak sensitivity of the binding of the agonist [3H]PIA to guanine nucleotides and seem to confirm that the adenosine A1 receptor is strongly and differently coupled than the alpha 2-adrenoceptor to the Gi-proteins in hamster adipocyte membranes.
Larrouy
D
D
INSERM U317, Institut Louis Bugnard, Université Paul Sabatier, CHU Rangueil, Toulouse, France.
Remaury
A
A
Daviaud
D
D
Lafontan
M
M
D000244:Adenosine Diphosphate / Q000378:metabolism; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D006224:Cricetinae; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D008066:Lipolysis / Q000502:physiology; D008297:Male; D008647:Mesocricetus; D037342:Pertussis Toxin; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism*; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D018341:Receptors, Adrenergic, alpha-2; D018047:Receptors, Purinergic P1; D010566:Virulence Factors, Bordetella; D014970:Xanthines; D010660:Phenylisopropyladenosine; D000244:Adenosine Diphosphate; C051360:1,3-dipropyl-8-cyclopentylxanthine; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins