Effect of streptozotocinâinduced diabetes on rat liver Na+/K+âATPase
2000
Sennoune, Souad | Gerbi, Alain | Duran, MarieâJosée | Grillasca, JoelâPaul | Compe, Emmanuel | Pierre, Sandrine | Planells, Richard | Bourdeaux, Madeleine | Vague, Philippe | Pieroni, Gerard | Maixent, JeanâMichel
Na+/K+âATPase during diabetes may be regulated by synthesis of its α and β subunits and by changes in membrane fluidity and lipid composition. As these mechanisms were unknown in liver, we studied in rats the effect of streptozotocinâinduced diabetes on liver Na+/K+âATPase. We then evaluated whether fish oil treatment prevented the diabetesâinduced changes. Diabetes mellitus induced an increased Na+/K+âATPase activity and an enhanced expression of the β1 subunit; there was no change in the amount of the α1 and β3 isoenzymes. Biphasic ouabain inhibition curves were obtained for diabetic groups indicating the presence of low and high affinity sites. No α2 andα3 isoenzymes could be detected. Diabetes mellitus led to a decrease in membrane fluidity and a change in membrane lipid composition. The diabetesâinduced changes are not prevented by fish oil treatment. The results suggest that the increase of Na+/K+âATPase activity can be associated with the enhanced expression of the β1 subunit in the diabetic state, but cannot be attributed to changes in membrane fluidity as typically this enzyme will increase in response to an enhancement of membrane fluidity. The presence of a highâaffinity site for ouabain (IC50â=â10−7âm) could be explained by the presence of (αβ)2 diprotomeric structure of Na+/K+âATPase or an as yet unknown α subunit isoform that may exist in diabetes mellitus. These stimulations might be related, in part, to the modification of fatty acid content during diabetes.
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