Effect of NaCl on composition and volume of cells of the rat papilla.

The composition and volume of the cells of an isolated rat papilla were measured in media in which NaCl was varied from 150 to 600 mM; KCl, from 2 to 20 mM; or which contained mannitol, 300 mM. Change in NaCl from 150 to 600 mM reduced cell volume by 25%, increased cell Na+ content by 250% but had no significant effect on cell potassium concentration or content. Increases in K+ concentration in the media did not affect cell water or cell sodium, but the cell potassium rose by an amount approximately 3 times the increase in the medium concentration. Mannitol reduced cell volume; the cell content of sodium and potassium did not alter, but the concentration of Na+ and K+ altered reciprocally with the change in cell volume. Similar changes were observed with liver slices. This study indicated that papillary cells maintain osmotic equilibrium by the accumulation of sodium. This accumulation may influence the metabolic activity of the medullary and papillary cells.