Gi3 does not contribute to the inhibition of adenylate cyclase when stimulation of an alpha 2-adrenergic receptor causes activation of both Gi2 and Gi3.
Agonist occupancy of the alpha 2-C10 adrenergic receptor in a stable clone (1C) of Rat 1 fibroblasts produced by transfection of cells with genomic DNA encoding this receptor causes the activation of both of the pertussis-toxin-sensitive G-proteins Gi2 and Gi3 [Milligan, Carr, Gould, Mullaney & Lavan (1991) J. Biol. Chem. 266, 6447-6455]. An IgG fraction from an antiserum (I3B) which identifies the C-terminal decapeptide of Gi3 alpha only was able to inhibit partially receptor stimulation of high-affinity GTPase activity. An equivalent fraction from an antiserum (AS7) able to identify the C-terminal decapeptide of Gi1 alpha + Gi2 alpha, but not Gi3 alpha, was also able to inhibit partially receptor stimulation of GTPase activity, and the effects of the two antisera were additive. By contrast, agonist-mediated inhibition of forskolin-amplified adenylate cyclase activity was abolished completely by the IgG fraction of antiserum AS7, but was not decreased by treatment with antiserum 13B. Based on the proportion of agonist-stimulated high-affinity GTPase which was prevented by each antiserum and on the measured membrane levels of Gi2 and Gi3, calculations indicated that essentially all of the cellular Gi3, but only 15% of the available Gi2, can be activated by the alpha 2-C10 adrenergic receptor in these cells. These results demonstrate that, although Gi3 is activated by alpha 2-adrenergic agonists in membranes of clone 1C cells, it does not contribute to the transduction of receptor-mediated inhibition of adenylate cyclase.
McClue
S J
SJ
Department of Biochemistry, University of Glasgow, Scotland, U.K.
Selzer
E
E
Freissmuth
M
M
Milligan
G
G
D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002999:Clone Cells; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007106:Immune Sera; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D000067956:Adenylyl Cyclase Inhibitors; D007106:Immune Sera; D011942:Receptors, Adrenergic, alpha; D011994:Recombinant Proteins; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases