Nanomolar concentrations of ouabain block ethanol-inducible Na+, K+-ATPase activity in brain

Abstract

The effect of low concentrations of ethanol on Na⁺, K⁺-ATPase activity, defined as ouabain-inhibitable ⁸⁶Rb⁺(K⁺) uptake, was investigated in a crude synaptosome preparation which was subject to minimal subcellular fractionation procedures. Moderate (20–30%) but potent (EC₅₀ = 3.8 mM) stimulation of total ouabain (1 mM)-inhibitable K⁺ uptake by ethanol was observed following incubation periods of up to 20 min. The activity of the ethanol-induced component of K⁺ uptake was antagonized by nanomolar concentrations of ouabain. Thus, the moderate stimulation of total ouabain-inhibitable K⁺ uptake by ethanol was attributable to the activation of a component of K⁺ uptake which was very sensitive (VS; IC₅₀ = 2.8×10⁻¹⁰ M) to inhibition by ouabain. Slightly higher concentrations of ouabain (10⁻⁹–10^−6.6 M) stimulated K⁺ uptake above control (no ethanol or ouabain) in both the absence and presence of ethanol. The selectivity of the VS-ethanol interaction was demonstrated by the lack of any ethanol effect on two other components of two other components of ouabain-inhibitable K⁺ uptake which accounted for inhibition of K⁺ uptake by concentrations of ouabain above 10^−6.6 M and were defined as sensitive (S; IC₅₀ = 10⁻⁶ M) and insensitive (I; IC₅₀ = 10⁻⁴ M) to ouabain. These results define the ethanol-inducible component of ouabain-inhibitable Na⁺,K⁺-ATPase activity and promote the view that changes in Na⁺,K⁺-ATPase-dependent ion translocation may contribute to ethanol intoxication in vivo.