[Comparative analysis of potassium and sodium flux across a muscle fiber membrane in a saline medium deficient in alkali metal cations].

Sodium and potassium fluxes from frog sartorius in magnesium-, choline- and Tris-Ringer solutions free of sodium and potassium have been studied wih the flame-emission technique. In the media examined the rate constant of potassium loss appeared to decrease as much as by 100 times when the internal sodium increases from 10 to 60-130 mumol/g. d. w. At. high internal sodium concentration, ouabain (10(-4) M) significantly increases the loss of potassium, whereas at low sodium concentration there is no such effect. The role of potassium reabsorption in the phenomena observed has been analyzed. No constant stoichiometry between the changes in ouabain-sensitive sodium fluxes and "reabsorbed" potassium fluxes has been found. With ouabain applied the time-course of shifts of these two fluxes are different. It is suggested that the effect of the internal sodium concentration and ouabain on potassium loss in sodium, and potassium-free media may be due not only to the reabsorption of potassium, but also to the change of potassium efflux itself.