Zonal changes in renal structure and phospholipid metabolism during reversal of potassium depletion nephropathy.

: Structural changes and membrane metabolism were studied in the enlarged kidney of potassium-depleted rats during dietary repletion with potassium. Transmission and scanning electron microscopy of kidneys revealed two patterns of involutionary change in the collecting tubules following potassium repletion. Autophagocytosis was observed within 3 hours in the hyperplastic cells of the inner red medulla, and progressive condensation and reduction in the number and size of lysosomes which had formed during potassium depletion were observed in the renal papilla. After 3 days of potassium repletion, all types of cells had a normal ultrastructural appearance. Alterations in membrane metabolism during autophagocytosis and organelle regression were assessed by measuring the in vivo breakdown of [14C]phosphatidylcholine, phospholipase A activity, and the rate of [14C]choline incorporation into phospholipid in papilla, inner red medulla, and inner cortex. In each tissue the rate of [14C]phosphatidylcholine breakdown increased and the rate of [14C]choline incorporation into phospholipid decreased during potassium repletion. Phospholipase A activity, which was depressed in potassium-depleted animals, increased in each renal zone by 12 hours after potassium repletion. The results indicate that reversal of potassium depletion nephropathy is associated with increased membrane phospholipid catabolism, loss of renal mass, and specific morphologic changes in different renal zones: lysosome regression in the papilla and autophagocytosis in the hyperplastic cells of the inner red medulla.