G sub(i)3 does not contribute to the inhibition of adenylate cyclase when stimulation of an alpha sub(2)-adrenergic receptor causes activation of both G sub(i)2 and G sub(i)3

Agonist occupancy of the alpha sub(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 G sub(i)2 and G sub(i)3. An IgG fraction from an antiserum (I3B) which identifies the C-terminal decapeptide of G sub(i)3 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 G sub(1)1 alpha + G sub(i)2 alpha , but not G sub(i)3 alpha , was also able to inhibit partially receptor stimulation of GTPase activity, and the effects of the two antisera were additive.