Stimulation of synaptosomal Na+,K(+)-ATPase by ethanol: possible involvement of an isozyme-specific inhibitor of Na+,K(+)-ATPase.
In synaptosomal preparations from rat cerebral cortex, ouabain-sensitive Rb+ uptake was stimulated by ethanol (20-80 mM). Based on differential sensitivity to ouabain, 80% of this Na+,K(+)-ATPase activity represented 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(+)-ATPase was selective for the activity of alpha 2/alpha 3 which was increased by 167% in the presence of 80 mM ethanol. In this concentration range, ethanol had no effect on alpha 1 activity. Exposure of synaptosomal preparations to EGTA increased basal (no ethanol) alpha 2/alpha 3 activity with no effect on alpha 1 activity. Further, ethanol no longer stimulated alpha 2/alpha 3 activity after EGTA treatment. An EGTA extract was concentrated and desalted to yield a fraction that selectively inhibited alpha 2/alpha 3 activity when reconstituted with EGTA-treated synaptosomal preparations. This inhibition was trypsin-sensitive, suggesting protein involvement, and was prevented by 80 mM ethanol. In the presence of the inhibitory protein fraction, ethanol stimulated Na+, K(+)-ATPase activity in EGTA-treated membranes with a dose-response like that observed with the crude (no EGTA) synaptosomes. We propose that the alpha 2/alpha 3 activity of Na+,K(+)-ATPase is subject to inhibitory 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.
Foley
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Department of Biochemistry, Microbiology and Molecular Genetics, University of Rhode Island, Kingston 02881-0812.
Rhoads
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology*; D006868:Hydrolysis / Q000187:drug effects; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000201:enzymology*
D007527:Isoenzymes; D000431:Ethanol; D004533:Egtazic Acid; D010042:Ouabain; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium