STIMULATION OF SYNAPTOSOMAL NA-ATPASE BY ETHANOL - POSSIBLE INVOLVEMENT OF AN ISOZYME-SPECIFIC INHIBITOR OF NA+,K+-ATPASE(,K+)

In synaptosomal preparations from rat cerebral cortex, ouabain-sensiti ve Rb+ uptake was stimulated by ethanol (20-80 mM). Based on different ial sensitivity to ouabain, 80% of this Na+,K+-ATPase activity represe nted activity of the alpha 1 isozyme while 20% was due to the alpha 2 and/or alpha 3 isozymes (alpha 2/alpha 3). Stimulation of Na+,K+-ATPas e was selective for the activity of alpha 2/alpha 3 which was increase d by 167% in the presence of 80 mM ethanol. In this concentration rang e, ethanol had no effect on alpha 1 activity. Exposure of synaptosomal preparations to EGTA increased basal (no ethanol) alpha 2/alpha 3 act ivity with no effect on alpha 1 activity. Further, ethanol no longer s timulated alpha 2/alpha 3 activity after EGTA treatment. An EGTA extra ct was concentrated and desalted to yield a fraction that selectively inhibited alpha 2/alpha 3 activity when reconstituted with EGTA-treate d synaptosomal preparations. This inhibition was trypsin-sensitive, su ggesting protein involvement, and was prevented by 80 mM ethanol. In t he presence of the inhibitory protein fraction, ethanol stimulated Na,K+-ATPase activity in EGTA-treated membranes with a dose-response lik e that observed with the crude (no EGTA) synaptosomes. We propose that the alpha 2/alpha 3 activity of Na+,K+-ATPase is subject to inhibitor y regulation and that ethanol stimulates this activity by releasing it from inhibition, an effect that may mimic in vivo deregulation of the enzyme by ethanol.