Tyrosine kinase phosphorylation of GABA_A receptors

Phosphorylation of purified bovine brain GABA_A receptors by the tyrosine kinase, pp60^v-src was examined. pp60^v-src phosphorylated two bands of 54-62 kDa and 48-51 kDa that migrated to approximately the same position as bands recognized by antisera against the β2 and γ2 GABA_A receptor subunits, respectively. Bacterially expressed proteins containing the putative large cytoplasmic loops of the β1 and γ2L subunits were phosphorylated by pp60^v-src, indicating that the phosphorylation sites are located in these subunit domains. The tyrosine kinase inhibitors, genistein and the tyrphostins B-42 and B-44, inhibited muscimol-stimulated ³⁶Cl^- uptake in mouse brain membrane vesicles (microsacs). The magnitude of the tyrphostin B-44-induced inhibition of muscimol-stimulated ³⁶Cl^- uptake was significantly reduced in microsacs that were lysed and resealed under conditions that inhibit phosphorylation. GABA-gated Cl^- currents were also inhibited by genistein and tyrphostin B-44 in Xenopus oocytes expressing α1β1 and α1βγ2L subunits. Consequently, protein tyrosine kinase-dependent phosphorylation appears to be another mechanism of regulating the function of GABA_A receptors.