Ethanol-induced inhibition of mouse brain adenosine triphosphatase activities: lack of interaction with norepinephrine in vitro.

The in vitro effects of ethanol on C57BL/6J mouse forebrain ATPase activities were investigated in the presence and absence of norepinephrine. Three enzyme activities (Na + K-ATPase, Mg-ATPase, and low affinity Ca-ATPase) were studied in forebrain homogenates using a colorimetric assay. The effect of norepinephrine on ethanol inhibition of Sprague-Dawley rat brain Na + K-ATPase activity was examined in selected experiments for direct comparison with the results obtained using mouse brain. Ethanol (250-2000 mM) inhibited all ATPase activities in a concentration-dependent manner. In each case the IC50 was well beyond what would be a lethal concentration in vivo. Ethanol inhibition of mouse forebrain Na + K-ATPase activity was competitive with regards to K+ ion concentration, but was uncompetitive for inhibition of Mg-ATPase and Ca-ATPase activities. Norepinephrine (0.1 mM) did not sensitize mouse brain Na + K-ATPase activity to ethanol-induced inhibition. In contrast, norepinephrine sensitized rat brain Na + K-ATPase to ethanol inhibition when tested simultaneously with mouse brain under identical conditions. These results cannot be explained by differences in assay conditions and suggest that the interaction between norepinephrine and ethanol inhibition of Na + K-ATPase activity may be species specific. Norepinephrine alone stimulated mouse and rat brain Na + K-ATPase activity when assayed in imidazole buffer, but not when assayed in tris buffer. Furthermore, 0.1 mM norepinephrine slightly antagonized the inhibitory effect of ethanol on mouse brain Mg-ATPase activity, but did not affect ethanol-induced inhibition of Ca-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)