This study was designed to investigate the effects of the potent vasoconstrictor, endothelin, on renal hemodynamics in rats in vivo, and in addition, to measure intracellular calcium ion ([Ca2+]i) in monolayers of renal vascular smooth muscle cells in culture using the fura-2 method. Endothelin (1 nmol) dramatically decreased renal blood flow from 7.0 +/- 0.5 ml/min to 2.6 +/- 1.0 ml/min, whereas it increased mean arterial pressure from 100 +/- 2 mmHg to 113 +/- 7 mmHg. These alterations persisted over 20 minutes in conscious and almost unrestrained rats. Endothelin (10(-8)-10(-7) mol/l) immediately increased [Ca2+]i, although the increase by endothelin (10(-9) mol/l) was relatively slow. The increase persisted in the presence of 1 mmol/l extracellular calcium. In the absence of extracellular calcium, only a small, transient increase of [Ca2+]i was observed. These results indicate that endothelin produces renal vasoconstriction and increases the [Ca2+]i in cultured renal vascular smooth muscle cells. The latter effect is dependent mainly on extracellular calcium.