Vascular smooth-muscle cells (VSMCs) isolated from genetically hypertensive animals show increased intracellular free calcium levels ([Ca2+]i) in response to endothelin-1 (ET-1). The differences in time course and distribution of Ca2+ increase after addition of ET-1 within the VSMCs are unknown. Therefore, ET-1-evoked changes in fluo-3 fluorescence were determined using a confocal laser scanning microscope in primary cultures of aortic smooth-muscle cells (ASMCs) from 12-week-old male Sprague-Dawley (SD) rats, Wistar-Kyoto (WKY) rats, and spontaneously hypertensive rats (SHR). Syto-11 staining enabled the assessment of intracellular free [Ca2+]i changes in the cytosolic ([Ca2+]c), perinuclear ([Ca2+]p), and nuclear ([Ca2+]n) regions. In the basal state, [Ca2+] was evenly distributed throughout the rat ASMCs. There were no significant differences in basal fluorescence values among the three strains. ET-1 evoked a concentration-dependent increase in fluo-3 intensity. The peak [Ca2+]i rise to ET-1 was much more rapid in ASMCs from SHR and WKY strains. The changes in [Ca2+]n were greater than in [Ca2+]c. Pretreatment of rat ASMCs with BQ-123 (an ETA antagonist) and BQ-788 (an ETB antagonist) abolished the rapid peak rise and the slow sustained elevation in [Ca2+]i, respectively. The nonselective antagonist bosentan attenuated both phases of the ET-1 response in all three strains. The ETB-selective agonist IRL 1620 evoked a significant elevation in [Ca2+]n values at 2 min in the ASMCs of SHR. These data suggest that ETA activation is linked to initial rapid increases in [Ca2+]c and [Ca2+]n, whereas ETB activation promotes slow [Ca2+]n signaling, particularly in ASMCs of SHR.