NA-K+ ATPASE CONCENTRATION IN DIFFERENT ADULT-RAT SKELETAL-MUSCLES ISRELATED TO OXIDATIVE POTENTIAL()

To investigate the relationship among fibre type, oxidative potential, and Na+-K+ ATPase concentration in skeletal muscle, adult male Wistar rats weighing 259 +/- 8 g (X(BAR) +/- SE) were sacrificed and the sol eus (SOL), extensor digitorum longus (EDL), red vastus lateralis (RV), and white vastus lateralis (WV) removed. These muscles were chosen as being representative of the two major fibre type populations: slow tw itch (SOL) and fast twitch (EDL, RV, WV) and exhibiting either a high (SOL, EDL, RV) or low (WV) oxidative potential. Na+-K+ ATPase concentr ation (pmol.g(-1) wet weight), measured by the [H-3]ouabain binding te chnique, differed (p < 0.01) only between the WV (238 +/- 7.9) and the SOL (359 +/- 9.6), EDL (365 +/- 10), and RV (403 +/- 12). Similarly, muscle oxidative potential as measured by the maximal activity of citr ate synthase was different (p < 0.01) only between the WV and the othe r three muscles. Citrate synthase activity (mu mol.min(-1).g(-1) wet w eight) was 4.0 +/- 0.7, 12.3 +/- 0.9, 9.1 +/- 0.7, and 11.3 +/- 1.0 in the WV, SOL, EDL, and RV, respectively. These results indicate that N a+-K+ ATPase concentration is not related to the speed of contraction but to the oxidative potential of the muscle. Since chronic activity i s a primary determinant of oxidative potential, it would be expected t hat increases in Na+-K+ ATPase would accompany increases in muscle uti lization.