(Na + ,K + )-ATPase activity in tubular systems of mouse cardiac and skeletal muscles.

Abstract

ATPase activity sensitive to ouabain was examined in both cardiac (ventricular) and skeletal (tibialis anterior) muscle cells of the mouse. Short-term fixation was combined with incubation in a medium designed to reduce artifactual deposition of lead phosphate. With incubation medium containing Na+ and K+, Pb3 (PO4)2 precipitate appears throughout the sarcoplasmic reticulum (SR) of both cardiac and skeletal cells. The precipitate generally is heavier in the junctional SR than in network SR, although the two regions are interconnected. Ouabain (1 mM) eliminates activity in the network SR of myocardial cells, but only reduces it in skeletal muscle cells. The total ATPase activity of junctional cisternae of the SR of myocardial cells does not appear to be reduced by ouabain, whereas the activity of the terminal cisternae of skeletal muscle is substantially diminished. The use of an incubation medium containing zero K+ reduces the level of activity, but not consistently. These data suggest that (Na+, K+)-ATPase is present in the network SR of both cardiac and skeletal muscle cells, and probably in the terminal cisternae of skeletal muscle cells.