| Abstrakt: |
Activity of NaK-ATPase, the biochemical equivalent of the sodium pump, may be reguiated by several factors including hormones, drugs, and inheritance. To evaluate further the possibility of genetic control, we investigated hepatic NaK-ATPase in mice selectively bred for differences in ethanol-induced sleep time, designated long sleep (LS) and short sleep (SS). In SS mice, specific acitivity of NaK-ATPase was 65% higher than in LS. Other plasma membrane enzymes were also increased in SS including alkaline phosphatase (176%), leucine aminopeptidase (115%), 5′-nucleotidase (49%). In contrast, basal adenylate cyclase and insulin binding, sodium do-decyl sulfate polyacrylamide gel electrophoresis patterns, and the cytosolic enzyme tyrosine aminotransferase were similar. Altered membrane lipid composition did not account for these differences since the cholesterol:phospholipid ratio and the enzyme activity response after addition of benzyl alcohol to membrane preparation were similar in both strains. Kinetic analysis of NaK-ATPase activity showed a similar Km, but Vmax was 60% increased in SS mice. Using sodium-dependent binding of [γ32P]ATP, a comparable increase in enzyme units was demonstrated. Since half-maximal ouabain inhibition was similar, differences in NaK-ATPase isoenzymes are unlikely. Differences in NaK-ATPase between LS and SS appear to be specific to the liver since activities were not different in kidneys and muscles. Induction of NaK-ATPase with tri-iodothyronine (T3) showed greater responses in LS (+53%) than in SS (+13%). These changes may relate to a post-receptor abnormality, since malic enzyme, a thyroid-responsive enzyme, was higher basally in LS mice, but similar to NaK-ATPase, the response to T3 administration was blunted in SS mice. To evaluate a possible link between NaK-ATPase activity and resistance to the hypnotic effect of ethanol, we examined inbred strains of mice with shorter (C57BL/6J) and longer (DBA/2J) ethanol sleep times. In contrast to LS/SS mice, NaK-ATPaae was higher In DBA and lower in C57. Our study adds an animal model of genetically controlled differences in NaK-ATPase, which is localized only to the liver. Although there seems to be no relationship between the different NaK-ATPase activity in LS and SS mice and their different response to ethanol, this model is of potential interest for the study of mechanisms leading to ethanol-induced liver disease. [ABSTRACT FROM AUTHOR] |
