Alterations in extracellular osmolality have a powerful inverse effect on aldosterone secretion that is associated with sustained changes in cell volume. With dispersed bovine glomerulosa cells grown in primary culture, the effects of alterations in osmolality on cell volume measured by the distribution of [14C]urea and [3H]mannitol were determined in the presence and absence of chloride. In the presence of chloride, decreases in osmolality increased cell volume, whereas angiotensin II (< 4 x 10(-9) M) did not affect cell volume. When chloride was removed from the medium (replacing chloride with the impermeant methyl sulfate ion), cell volume decreased significantly, but basal aldosterone secretion was not altered. In the absence of chloride, the increases in cell volume, cytosolic calcium concentration, and aldosterone secretion induced by decreases in osmolality were significantly suppressed. The replacement of chloride with the methyl sulfate ion suppressed the increases in both cytosolic calcium concentration and aldosterone secretion induced by low (< 4 x 10(-9) M) but not high (4 x 10(-8) M) concentrations of angiotensin II. The results suggest that reductions in osmolality increase cell volume, partly by inducing an influx of chloride ions that contributes to the total net influx of water. Reductions in cell volume caused by an increase in osmolality or by replacing the chloride ion with the impermeant methyl sulfate ion may induce alterations in membrane stretch that may decrease the angiotensin II-induced increase in cytosolic calcium concentrations, which in turn suppresses aldosterone secretion.
Simultaneous changes of cell volume and cytosolic calcium concentration in macula densa cells caused by alterations of luminal NaCl concentration
