Interaction of ethanol and catecholamines on rat brain (Na+ + K+)-ATPase

Abstract

The (Na+ + K+)-ATPase activity in rat brain homogenates was stimulated by either d(+)- or l(−)-noradrenaline (NA) or by dopamine (DA) when vanadium-contaminated ATP was used as substrate, but not with vanadium-free ATP. Addition of 6.25–50 mM ethanol (EtOH) alone had no effect on the activity of dilute (1:2600) homogenates; however, in the presence of l-NA or DA, but not of d-NA, it produced a concentration-dependent reduction of activity below control values, regardless of which ATP was used. The minimum concentrations of catecholamine producing sensitization of ATPase to EtOH were 10−12 M l-NA and 10−7 M DA. With concentrated (1:65 or 1:78) homogenates, EtOH produced concentration-dependent inhibition without addition of exogenous catecholamines. The inhibition of ATPase by EtOH in the concentrated homogenate was decreased by elevation of K+ concentration, and was prevented in both dilute and concentrated homogenates by phentolamine but not by propranolol. The findings suggest that the action of NA or an α receptor may alter the enzyme microenvironment, by an as yet unknown mechanism, rendering it more susceptible to inhibition by EtOH.