A patch clamp study of γ‐aminobutryic acid (GABA)‐induced macroscopic currents in rat melanotrophs in cell culture

Abstract

1 The macroscopic currents induced in cultured rat melanotrophs by exogenous γ-aminobutyric acid (GABA) were analysed using the patch clamp recording technique. 2 Using various concentrations of intra-and extracellular chloride it was demonstrated that the conductance activated by GABA was chloride selective. Since these currents were blocked with bicuculline and enhanced with chlordiazepoxide the involvement of GABA_A receptors similar to those in the CNS is indicated. 3 When chloride was symmetrically distributed across the membrane the voltage/current relationship was linear; pronounced rectification of GABA mediated currents was evident when there was an asymmetrical distribution of chloride. 4 With concentrations of GABA greater than 10 μm a fading of the current was seen during prolonged (5–10 s) applications. This effect appeared to be due to a decline of conductance rather than a shift of the chloride equilibrium potential. 5 Values for the Hill coefficient derived from dose-response curves suggested that the binding of 2 molecules of GABA to the receptor is required for the activation of the chloride channel. 6 There was no indication of a direct, GABA_B receptor-mediated change of conductance.