Expression of the GABA_B receptor in <i>Xenopus</i> oocytes and inhibition of the response by activation of protein kinase C

Abstract

The functional GABAB receptor was expressed in Xenopus oocytes by injecting mRNA obtained from the cerebellum of the rat. Application of GABA in the presence of bicuculline induced a hyperpolarization under current-clamp conditions and an outward current under voltage-clamp conditions. Baclofen mimicked the effect of GABA in the presence of bicuculline, and the effect of baclofen was antagonized by phaclofen. The GABA-induced outward current was slightly inhibited by treatment with GDP-beta-S and was completely inhibited by treatment with GTP-gamma-S. The activation of protein kinase C by 12-O-tetradecanoylphorbol-13-acetate (TPA), but not 4 alpha-phorbol-12,13-didecanoate, suppressed the GABAB receptor-mediated hyperpolarization, and the effect of TPA was antagonized by sphingosine. Thus, activation of protein kinase C inhibits the expressed GABAB receptor-mediated response.