Sepsis increases skeletal muscle sodium, potassium-adenosinetriphosphatase activity without affecting messenger RNA or protein levels.

Abstract

Previous studies suggest that sodium, potassium-adenosinetriphosphatase (Na+, K(+)-ATPase) activity in skeletal muscle is increased during sepsis, but the molecular mechanisms are not well understood. We tested the hypothesis that increased muscle Na+,K(+)-ATPase activity during sepsis is associated with increased expression of messenger RNA for the Na+,K(+)-ATPase alpha-1, alpha-2, and beta-1 subunits and increased amounts of the enzyme protein. Extensor digitorum longus muscles were harvested from rats 16 hours after induction of sepsis by cecal ligation and puncture or sham operation. The Na+,K(+)-ATPase activity was determined spectrophotometrically. Messenger RNA levels for the alpha-1, alpha-2, and beta-1 subunits of Na+,K(+)-ATPase were determined by Northern blot analysis. Enzyme protein levels were measured by Western blot analysis and tritium-ouabain binding assay. Muscle Na+,K(+)-ATPase activity was 46 percent higher in rats that had sepsis than in rats that underwent sham operation (p < .05). No significant differences between septic and control groups were noted in messenger RNA levels for the Na+,K(+)-ATPase subunits. Western blot analysis and tritium-ouabain binding revealed no difference in enzyme protein expression between septic and control animals. Results suggest that sepsis increases skeletal muscle Na+,K(+)-ATPase activity without affecting enzyme messenger RNA or protein levels. The results are consistent with an increased catalytic constant for individual Na+,K(+)-ATPase protein units, an atypical mechanism for this enzyme.