Effects of in vitro ethanol on the brain cation pump in alcoholics and controls

In vivo ethanol exposure reduces in vitro Na⁺K⁺-adenosine triphosphatase (Na⁺K⁺-ATPase) sensitivity to ethanol in some animal models, but very little is known about the effects of ethanol on human brain Na⁺K⁺-ATPase. Cerebral cortex homogenates from 13 male alcoholic and 9 control subjects were assayed for K⁺-p-nitrophenylphosphatase (K⁺-pNPPase, a measure of Na⁺K⁺ ATPase) and Mg²⁺-pNPPase activities at 37° for 20 min in 75 mM imidazole-HCl (pH7.4), 5mM p-nitrophenylphosphate, 5mM MgCl₂, and 20 mM KCl, with or without 1 mM ouabain. Native K⁺-pNPPase activities were similar in control and alcoholic brains (61.5 ± 3.5 vs 55.3 ± 3.1 nmol/mg/min). In vitro exposure to a near lethal ethanol level (0.5%, or 110 mM) was without effect, whereas 5% ethanol inhibited IC-pNPPase activity by about 28% (P < 0.001) in both groups. Both 0.5 and 5% ethanol in vitro significantly stimulated Mg²⁺-pNPPase activity (1-2% and 19-20%, respectively). By comparison, mouse brain K⁺-pNPPase was inhibited significantly by in vitro ethanol, and Mg²⁺-pNPPase activity was unaffected. Ethanol levels attainable in humans may not be sufficient to alter significantly brain Na⁺,K⁺-ATPase activity.