[Ultrastructural-cytochemical features of the plasma membrane of sodium-transporting cells]

Electron microscopic and biochemical studies of the ATP-ase activity in different regions of the nephron and in the kidney microsomal fraction of the rat have revealed a pronounced increase of the total and Na+-+K+-ATP-ase activity in the process of compensatory hypertrophy. A decrease of the enzymatic activity was noted predominantly in proximal tubules under loading the animals by isotonic NaCl solution and after adrenalectomy--mainly in distal tubules. This speaks of the inhibition of the sodium-reabsorbing system in them. The transport of isotonic fluid in collecting tubes is accompanied by widening intercellular lacunae together with an increase of the ATP-ase activity of the lateral plasmic membrane of neighbouring cells. The data obtained suggest a close correlation between the electron-microscopically revealed ATP-ase activity of the plasmic membrane of tubular cells and the functional activity of the sodium-transporting system. A morphological equivalent of the sodium pump is a plasmolemma--mitochondrial pump which is characterized by: a) well developed foldness of the basal plasmic membrane where the enzymatic system is disposed; b) the high total and Na++K+-ATP-ase activity cytochemically and biochemically revealed; c) numerous regularly disposed mitochondria, having close contacts with the folds of the basal plasmic membrane.