[Sodium flux across a muscle fiber membrane in saline media lacking sodium and potassium].

Unidirectional sodium fluxes were measured in frog sartorius muscle with radioisotopes and emission techniques. A comparison was made of sodium rate constants, evaluated from the efflux of sodium preexisting in muscle, and from the efflux of 22Na. The rate constants for sodium influx and efflux were determined in solutions in which sodium and potassium were substituted for magnesium, choline and tris. Ouabain inhibits about 40% of sodium efflux investigated. In sodium- and potassium -free media, the rate constant for sodium efflux does not depend on the internal sodium concentration both for ouabaine-resistant and ouabain-sensitive components. The ouabain-sensitive and ouabain-resistant sodium fluxes and operation pump in cation deficient medium have been discussed.