The β1 and γ2L subunits of the γ-aminobutyric acid type A receptor (GABAR) contain phosphorylation sites for PKC. To determine the effect of PKC on GABAR function, whole-cell recordings were obtained from mouse fibroblasts expressing recombinant α1β1γ2L receptors, and catalytically active PKC (PKM) was applied via the recording pipette. The first experiment was a population study. Intracellular application of PKM increased GABAR currents, and the enhancement was antagonized by coapplication of the PKC inhibitory peptide. No acceleration or deceleration of GABAR desensitization was observed. The second experiment was a reimpalement study in which paired recordings were made successively from individual cells. Enhancement of GABAR currents by PKM was again obtained. PKM increased GABAR currents at high (>10 μM) but not at low (<10 μM) GABA concentrations, resulting in increases in both EC50 and maximal GABAR current. Thus, PKC phosphorylation enhanced recombinant α1β1γ2L GABAR current by increasing maximal current without increasing the affinity of GABA for the GABAAs.
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