The role of phosphorylation in the activity and mercury modulation of GABA-induced currents in rat neurons.

The role of protein kinase A (PKA) and protein kinase C (PKC) in the function and modulation by mercury chloride of the GABA(A) receptor-chloride channel complex was studied with rat dorsal root ganglion cells using the whole-cell patch clamp technique. When added to the internal pipette solutions, both KT 5720, a selective PKA inhibitor, and calphostin C, a selective PKC inhibitor, increased the maximal current and shifted the EC50 for GABA in the direction of higher GABA concentrations. GABA-activated currents were decreased by the addition of 5 mM cAMP to the internal pipette solution, and by external perfusion of 100 nM phorbol 13-myristate 13-acetate. Mercury chloride potentiation of GABA-activated currents was blocked by internal application of 5 mM cAMP. PKA in the recording pipette abolished the mercury chloride potentiation of GABA-activated currents. In contrast, 0.56 microM KT 5720, but not calphostin C, in the internal pipette solution enhanced the effect of mercury chloride. In conclusion, both PKA and PKC negatively regulate the activity of the GABA(A) receptor-channel complex probably through phosphorylation of the receptor, and the PKA system underlies the mechanism of mercury chloride potentiation of GABA-activated currents.