The purpose of this study was to examine whether different mechanisms might underlie the changes in intracellular calcium concentration ([Ca2+]i) stimulated by high and low concentrations of endothelin, and whether atrial natriuretic factor (ANF) has an inhibitory effect on endothelin-induced [Ca2+]i changes in cultured rat vascular smooth muscle cells (VSMCs). In calcium-replete buffer, cultured monolayers of rat VSMCs superfused with endothelin at a high concentration (10 nM) exhibited a marked transient rise in [Ca2+]i, followed by a sustained elevation, whereas a low concentration of endothelin (0.1 nM) induced a sustained monophasic elevation. When calcium-free buffer was used, 10 nM endothelin induced a transient rise in [Ca2+]i of lesser amplitude, whereas 0.1 nM endothelin did not produce a significant rise. Pretreatment of VSMCs with ANF and cosuperfusion with endothelin failed to inhibit either transient or sustained endothelin-induced changes in [Ca2+]i in calcium-replete buffer.