[The "anomalous" relationship between the concentration of potassium in the medium and the membrane potential of muscle fibers with a decreased intracellular potassium concentration. II. Rate of forward and reverse K42 transport through muscle fiber membranes in saccharose-sulfate solutions with potassium concentrations of 2.5 and 75 mM].

The measurements were made of the unidirectional potassium fluxes, the rate constants and the permeability coefficient. At external potassium 2.5 mM, the outflux and influx are 10--15, and 22-29 micromol/h g d. wt, respectively, and the net flux is comparable with the unidirectional fluxes. At external potassium 75 mM, the unidirectional fluxes increase up to 70--80 micromol/h, g d. wt. and the net flux does not exceed 0.1 of the unidirectional one. The outflux rate constant/influx rate constant ratio for both the potassium concentrations is about 1.5 times below the Ussing's ratio. This effect cannot be accounted for the single file phenomenon since it is independent of the direction and value of the net potassium flux. The discrepancy between the measured membrane potential and EK may, to some extent, be due to peculiarities of potassium movement.