The mechanism by which intracellular GABA increases Cl- outward permeability across Deiters' neurone plasma membranes

The present experiments aimed to clarify how the interaction of gamma-amino-butyric acid (GABA) with its receptors on the cytoplasmic side of the Deiters' neurone plasma membrane causes Cl- permeability to be higher in the in----out than in the opposite direction. To this end, the rate of 36Cl- in----out passage was studied in basal conditions, with GABA on the cytoplasmic side and in the presence of both GABA and an increased ionic strength buffer on that side. The results show that an increase in ionic strength reverses the GABA effect of 36Cl- permeability. The reversion being caused by changes in the buffer on the intracellular but not on the extracellular side. Our interpretation of this result is that the interaction of GABA with its cytoplasmic side receptors induces an exposure of positive charges only at the intracellular mouth of the intraneuronal GABA gated Cl- channels. This asymmetry would be the basis of the reported higher Cl- permeability in the in----out direction.