Ultrastructural changes in the renal papillary cells of rats during maintenance and repair of profound potassium depletion.

In rats with long-term diet-induced potassium depletion, the cytoplasm of markedly enlarged papillary cells was mainly occupied by membrane-bound droplets, many of which acquired massive proportions. Both free and attached ribosomes were decreased, the Golgi apparatus was inconspicuous and there was a paucity of mitochondria. Despite the overwhelming accumulation of droplets with concomitant loss of normal metabolic organelles, cell death did not occur. With potassium repletion, the organelles readily proliferated regardless of the progression of droplet dissolution. The shrinkage of the droplets was accompanied either by disintegration of the limiting membrane or by disappearance of the constituents within an intact membrane. Microtubules were conspicuous in many of the cells undergoing gradual reduction in size. These cytoplasmic changes in renal medullary cells of rats during long-term potassium depletion and immediate post-repletion periods essentially represented the consequences of maintenance and repair of a storage process.