The response to potassium of the Na-K pump ATPase in low-K red blood cells from cattle at birth and in later life.

It is shown that in low-K red blood cells of cattle the apparent affinity for K(1/Kapp K) at an inhibitory site of the Na-K ATPase increases markedly during the first 3 months of life. This site probably is the Na accepting site at the internal membrane surface and the change in Kapp K reflects an increase in KNa/KK, the ratio of the true dissociation constants. This effect may explain the concomitant fall in cellular K concentration.