Abstract
We have examined the effects of diabetes, fasting, and refeeding on Na + K + -adenosine triphosphatase (ATPase) activity and its catalytic αII subunit gene expression in skeletal muscle. Two hypoinsulinemic states, streptozotocin-induced diabetes and 48-hour fasting caused a significant decrease ( P < .05) in skeletal muscle Na + K + -ATPase activity and a marked increase ( P < .01) in the levels of αII subunit mRNA. A decrease in enzyme activity was observed on the 2nd and the 14th day of diabetes, whereas an increase in αII mRNA levels was found only on the 14th day. The levels of αl mRNA were not affected, while the levels of mRNA of the structural β subunit were decreased on the 14th day of diabetes. Correction of hyperglycemia with insulin restored enzyme activity and αII isoform mRNA levels toward normal in diabetic animals. Refeeding for 48 or 72 hours restored these parameters to normal in skeletal muscle of previously fasting rats. These observations suggest that a decrease in muscle Na + K + -ATPase activity may lead to a compensatory increase in its αII subunit gene expression. The levels of insulin and not of glycemia appear to be critical in modulating Na + K + -ATPase activity and gene expression.
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