Permeability of Erythrocytes to Radioactive Potassium

The diffusion coefficients for the exchange of potassium across the membrane of erythrocytes of humans, rats, and rabbits have been determined by the use of artificially radioactive potassium, both into and out of the erythrocytes both in vitro and in vivo. The diffusion coefficients found in minutes(-1) were 0.2 to 0.25 x 10(-3) for human, 0.32 to 0.665 x 10(-3) for rabbits, and 1.0 x 10(-3) for rat erythrocytes. Rabbit erythrocytes appear to be more permeable in vivo. Reasons are advanced to explain the failure of earlier workers to demonstrate appreciable exchange of potassium in erythrocytes.