Rapid effects of aldosterone on free intracellular calcium in vascular smooth muscle and endothelial cells: subcellular localization of calcium elevations by single cell imaging.

Rapid in vitro effects of aldosterone on the intracellular concentrations of sodium, potassium and calcium, cell volume and the sodium-proton-antiport have been described in human mononuclear leukocytes and vascular smooth muscle cells (VSMC). These nongenomic effects are signalled through membrane receptors with a high affinity for aldosterone, but not for cortisol, and through the phosphoinositide pathway. In the present study, we demonstrate that free intracellular calcium is increased rapidly by aldosterone in VSMC and endothelial cells (EC) as determined by single cell imaging of Fura2-fluorescence. In VSMC, calcium elevation is localized to the perinuclear region whereas in EC, a predominant increase of subplasmalemmal calcium is seen. In VSMC, effects are half maximal at 0.1 nM aldosterone; cortisol is inactive up to 0.1 microM. These data show that intracellular signalling for aldosterone also involves calcium, but the subcellular localization of this signal varies between cell types.