A comparative study of the maturation of NaK-ATPase activity in different nephron segments

Abstract

In the kidney the development of deep nephrons preceeds the development of superficial (s̄f) nephrons and the structural maturation of proximal tubular (PT) segments preceeds the structural maturation of distal tubular segments. NaKATPase is present in all nephron segments. The comparison between the development of NaKATPase activity in PT and thick ascending limbs of Henle (TAL) in deep and sf nephrons can therefore yield information about the relative importance of genetic and environmental factors for enzymatic differentiation. NaKATPase activity was determined in isolated rat tubular segments with Doucet's method (AJP 1979). NaKATPase activity increased in both PT and TAL till the age of 40 days. In PT development was linear while in TAL development was accelerated between 16 and 20 days. The developmental pattern for NaKATPase was the same in cortical and medullary TAL and the same in sf and deep PT.Serum corticosterone was determined with RIA. It was low till 16 days, then increased rapidly to reach adult values at 20 days. Adrenalectomy inhibited the development of NaKATPase. Treatment with betamethasone (up to 60 μg/100 g) precociously induced NaKATPase in TAL at 16 days of age and in PT at 10 to 20 days of age. PT concentration of cytosolic glucocorticoid receptors determined with isoelectric focusing was significantly higher in 20- than in 40-day-old rats.Conclusion: The enzymatic differentiation is typical for each cell type. In a given cell type extracellular factors appear to influence the enzymatic differentiation simultaneously and irrespective of embryonic age.