Osmolality and potassium cause alterations in the volume of glomerulosa cells

Alterations in extracellular osmolality have a powerful inverse effect on aldosterone secretion and potassium- and angiotensin-stimulated aldosterone secretion. Whether alterations in extracellular osmolality produced sustained changes in cell volume that may contribute to the regulation of aldosterone secretion is not known. Using dispersed bovine glomerulosa cells grown in primary culture, the effect of alterations in osmolality on cell volume, measured by the distribution of [14C]urea and [3H]inulin and videometric analysis of the surface area of glomerulosa cells, was determined. Alterations in osmolality had an inverse effect on cell volume and surface area. Changes in cell volume induced by exposure to anisotonic medium were 52% greater (P > 0.02) than that predicted by the changes in osmolality. Increases in potassium concentration also caused sustained (1-h) concentration-dependent increases in cell volume and surface area. Angiotensin-II did not increase glomerulosa cell volume, but did produce a small dose-dependent transient increase in cell surface area. The results demonstrate that alterations in osmolality do cause sustained changes in cell volume, and thus, membrane stretch could be an important part of the cellular mechanism responsible for causing osmolality-induced changes in the cytosolic calcium concentration and subsequent alterations in aldosterone secretion. Alterations in membrane stretch may also be an important component of potassium-induced, but not angiotensin II-induced, aldosterone secretion.