Intracellular GABA-activated in-->out permeation of chloride across the Deiters' neuron membrane: modulation by phosphorylating activities.

The modulation of intracellular GABA activated 36Cl- in-->out permeation across single Deiters' neuron membranes has been studied in a microchamber system. Addition of Mg2+/ATP on the membrane cytoplasmic side reduces strongly the GABA effect as does ATP alone. However, the greatest inhibition of the GABA effect is given by the addition of Mg2+ to the intracellular side buffer: a complete block of the stimulation by GABA of 36Cl- in-->out permeation. This is interpreted as due to the presence in this case of a constant concentration of exogenous Mg2+ acting together with endogenous ATP in the small cytoplasmic layer on the membrane inner side. The addition of ADP to Mg2+/ATP increases the inhibitory effect of the latter. This is presumably due to an extra increase of ATP, locally under the membrane, due to phosphorylation of ADP by endogenous phosphocreatine. Overall, the data confirm that phosphorylating conditions impair the intracellular GABA action on 36Cl- in-->out permeation.