Brain NaK-ATPases in mice differentially sensitive to alcohols

Solubilization of benzodiazepine receptors from long- and short-sleep mice

Previous studies have shown that long-sleep (LS) and short-sleep (SS) mice, which were selectively bred for differential responses to the sedative-hypnotic actions of ethanol, also differ in response to several other agents that act at the GABAergic receptor. Binding at cortical benzodiazepine receptors is enhanced differentially by GABA and ethanol in membranes prepared from the two lines of mice with SS receptors enhanced to a greater extent. Heat denaturation studies and other biochemical characterizations of these receptors suggest that the GABAergic receptor complex from the two lines of mice differs. The present study examined whether perturbation of receptor-membrane interactions by treatment with detergent altered either GABA enhancement of [3H]flunitrazepam binding or ethanol enhancement of this binding. Octylglucopyranoside (OCTG), 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS), or deoxycholate solubilization of cortical membranes resulted in a loss of the LS/SS difference in GABA enhancement. Ethanol's effects on binding were altered differently from those of GABA by treatment with OCTG as an increase, not a decrease, in enhancement was observed in both lines of mice. These results suggest that protein-membrane interactions play an important role in mediating LS/SS differences in the allosteric interactions within the GABAergic receptor complex.

Effects of ethanol on ouabain inhibition of mouse brain (Na+,K+)ATPase activity

Plots of ouabain inhibition of mouse cerebral cortical (Na+,K+)ATPase activity fitted a two-site model significantly better than a one-site model, consistent with the presence of two forms of the enzyme with different affinities for ouabain. The fraction of enzyme activity with high affinity for ouabain (HAO: Ki = 500 nM), suggested to be localized neuronally, constituted the major portion (60-70%) of activity. Ouabain inhibition of both components of enzyme activity was reduced as KCl concentrations were increased. In vitro, only high concentrations of ethanol affected (Na+,K+)ATPase activity and ouabain inhibition of activity. Ethanol (500 mM) selectively reduced the activity, and increased the sensitivity to ouabain inhibition, of the HAO component, with no significant effect on the low-affinity (LAO) component. On the other hand, following chronic treatment of mice with ethanol in vivo, in a paradigm that produced tolerance and physical dependence, the sensitivity to ouabain of the HAO form of the enzyme was selectively increased. The relative proportions, and the activities of the HAO and LAO components, were not altered. The effects of ethanol, added in vitro, on the HAO component were decreased in ethanol-tolerant animals. The selective effect of chronic ethanol ingestion on (Na+,K+)ATPase activity indicates the specificity of action of ethanol in the CNS.

(Na+,K+)-ATPase and noradrenergic function: effects of chronic ethanol

The experiments in this paper examined interactions between ethanol and repeated noradrenergic stimulation in vivo on regulation of (Na+,K+)-ATPase. The increase in ouabain binding and K+-phosphatase activity associated with (Na+,K+)-ATPase in rats treated with repeated yohimbine injections was prevented by chronic ethanol. Ethanol did not affect the yohimbine-induced alterations in noradrenergic receptor binding or in content of the norepinephrine metabolite 3-methoxy-4-hydroxyphenylglycol, showing that prevention of noradrenergic stimulation of (Na+,K+)-ATPase was not caused by a decrease in availability of norepinephrine. In addition, norepinephrine depletion with the neurotoxin DSP4 did not prevent the increases in (Na+,K+)-ATPase indices during chronic ethanol treatment, showing that they did not result from increased norepinephrine exposure. These results suggest that chronic ethanol reduces sensitivity of (Na+,K+)-ATPase to norepinephrine in vivo, possibly as a consequence of membrane effects of ethanol tolerance.

Neuronal membrane enzymes in rat lines selected for differential motor impairment by ethanol

Neuronal membrane enzyme activities were determined in naive and ethanol-treated (30 min after 2 g/kg) male and female rats of lines developed for more (ANT) and less (AT) ethanol-induced motor impairment. Ethanol did not affect acetylcholinesterase, (Na+K)-ATPase or 5'-nucleotidase activities, but adenylate cyclase activities were lowered in both cerebellum and cerebrum. Cerebral acetylcholinesterase activities were higher in ANT than AT rats. No consistent line difference was observed regarding (Na+K)-ATPase activities. Slightly higher cerebellar 5'-nucleotidase activities were found in the ANT line. Cerebellar adenylate cyclase levels were substantially higher in the AT line. No line differences were displayed in the activation of adenylate cyclase activity by dopamine or norepinephrine. It is concluded that ethanol in vivo may inhibit neuronal adenylate cyclase activity and that cerebellar phosphorylation may be a regulator of motor impairment. Cholinergic mechanisms may also be connected to the ethanol-induced motor impairment.

Ethanol and temperature effects on five membrane bound enzymes

The effects of ethanol on the activities of five membrane bound enzymes were determined using a crude membrane preparation obtained from cortex of long-sleep (LS) and short-sleep (SS) mice. These two mouse lines were selectively bred for differences in duration of ethanol-induced sleep time. The enzymes studied were two forms of NaK-ATPase, Mg-ATPase, 5'nucleotidase, and acetylcholinesterase. Arrhenius plots of the ethanol-temperature-enzyme activity studies indicate specificity in ethanol's actions. NaK-ATPase activity consists of two enzymes which were distinguished by sensitivity to ouabain. The Arrhenius plot of the high ouabain sensitivity enzyme (low Ki) exhibited a transition temperature which was reduced twice as much by ethanol in LS membranes as in SS membranes. Ethanol did not affect the transition temperature of the high Ki NaK-ATPase but the control (no ethanol) transition temperature was 2.7 degrees higher in SS membranes. Arrhenius plots of Mg-ATPase activity did not exhibit a transition temperature and ethanol did not alter enzyme activity. Ethanol did not alter the transition temperatures of 5'nucleotidase or acetylcholinesterase but the control transition temperature for acetylcholinesterase was 2.3 degrees higher in SS membranes. These results indicate specificity in ethanol's actions on membranes and that inhibition of the lipid-enzyme interactions for the low Ki NaK-ATPase is correlated with the difference in sensitivity to ethanol seen between the LS and SS mice.