Sepsis increases the plasma membrane content of α1 and α2 isoforms of Na⁺-K⁺ adenosine triphosphatase in rat skeletal muscle

Hypothesis: Increased Na⁺-K⁺ adenosine triphosphatase (ATPase) activity in skeletal muscle during sepsis is caused by transient increases in enzyme content within the plasma membrane. Design: Randomized controlled study. Setting: University laboratory. Intervention: Eighty-eight adult male Wistar rats were randomly assigned to undergo cecal ligation and puncture (CLP) or sham operation. Main Outcome Measures: Gastrocnemius muscles were harvested 6, 12, 24, and 48 hours after operation and Na⁺-K⁺ ATPase activities were measured spectrofluorimetrically. Messenger RNA (mRNA) levels for the α1 and α2 isoforms of Na⁺-K⁺ ATPase were determined by Northern blot analysis. Crude membranes, internal membranes, and purified plasma membranes were isolated from gastrocnemius muscles and protein levels of α1 and α2 isoforms were determined by Western blot analysis. Results: Na⁺-K⁺ ATPase activity in the CLP group was significantly higher compared with the sham group 24 hours after operation (P<.05). However, there were no differences between the sham and CLP groups 6, 12, or 48 hours after operation. No significant differences between the CLP and sham groups were noted in mRNA levels for Na⁺-K⁺ ATPase α1 and α2 isoforms. Western blot analysis revealed that the plasma membrane (but not internal membrane or crude membrane) content of α2 and α1 isoforms from the CLP group was significantly increased compared with the sham group 24 hours after operation (P<.05). Conclusions: Na⁺-K⁺ ATPase activity increases 24 hours after CLP in gastrocnemius muscle and then declines. This increase is caused by increased Na⁺-K⁺ ATPase protein levels in the plasma membrane.