Postnatal development of rat kidney plasma membrane Na-K-ATPase

The postnatal development of the sodium transport mechanism in the rat kidney, as judged by the activity of renal plasma membrane Na-K-ATPase, was studied. Highly purified kidney plasma membranes as verified by electron microscopic and enzyme examinations, were used. Na-K-ATPase activity (mumol Pi/mg protein/h) increases exponentially from 16.9 +/- 1.94 found at birth to the mature level of 43.1 +/- 2.16 reached at the age of 41 days. This finding paralleled our results of SDS-polyacrylamide gel disc electrophoresis, showing a completely differentiated plasma membrane protein structure at birth, the maturation of which proceeds only as quantitative enrichment of some protein fractions in the further postnatal period.