RELATION BETWEEN α-ISOFORM AND PHOSPHATASE ACTIVITY OF Na+,K+-ATPase IN RAT SKELETAL MUSCLE FIBER TYPES

In skeletal muscle the relationship between Na+,K+-ATPase activity and isoform content remains controversial (9,6). It could be due to the fiber-type content, membrane isolation and analytical methods. We investigated the distribution of subunit alpha 1 and alpha 2 Na+,K+-ATPase catalytic isoforms and the Na+,K+-ATPase activity in isolated membranes from white (type I and glycolitic fibers) and red (type II and oxidative fibers) skeletal muscles. Red Gastrocnemius and White Gastrocnemius muscles were sampled from 8 week-old female Wistar rats and crude membranes were performed. The Na+,K+-ATPase activity and membrane distribution of Na+,K+-ATPase alpha 1 and alpha 2 isoforms were assessed by ouabain sensitive K-phosphatase (Kpase) measurements and Western Blot respectively. The Na+,K+-ATPase activity was 6 fold lower in White Gastrocnemius membranes than in Red Gastrocnemius membranes. The alpha 1 and alpha 2-isoform levels are higher in RG than in White Gastrocnemius. The alpha 1 and alpha 2-subunit Red Gastrocnemius content was significantly higher than in WG. The correlation between crude membrane Kpase activity and both catalytic alpha-subunit of the Na+,K+-ATPase exist. These data suggest that the Na+,K+-ATPase phosphatase activity correlates with the alpha 1 and alpha 2 isoforms levels in Red Gastrocnemius and White Gastrocnemius and confirms the fiber-specific Na+,K+-ATPase catalytic alpha-subunits and alpha 2-isoform as the major catalytic isoform in rat skeletal muscle.