The subcellular location of potassium flux pathways in frog skeletal muscle

The influence of ouabain and physostigmine on 42K and 86Rb uptake in isolated from sartorii with normal [Na]i(12-14 mmol.kg -1 wet weight) and low [Na]i (6 mmol.kg-1 wet weight) was compared. Both in normal sodium and in low sodium muscles application of 10-3 M physostigmine reduces potassium influx by about 70%. About one forth of potassium-uptake in normal-sodium muscles is inhibited by ouabain (10-4 M) and only a very slight fraction of potassium uptake is ouabain-sensitive in low-sodium muscle. The effects of ouabain and physostigmine on 42K influx are additive. The greater parts of the Rb-fluxes are through the ouabain-sensitive pathway. Glycerol treatment has no effect on ouabain-sensitive channels although it inhibits markedly the K-flux through the physostigmine-sensitive pathway. The results suggest that the Na-K-ATPase is located in the surface membrane while most of the physostigmine-sensitive K-exchange is within the tubules.