The aim of this study was to investigate ANG II induced Ca²⁺ signaling in freshly isolated afferent arterioles (AA) from two-kidney, one-clip hypertensive (2K1C) rats, which have an elevated plasma and renal angiotensin II (ANG II) level, and different perfusion pressure and vascular tone in the clipped and non-clipped kidney. The Ca²⁺ responses in vessels from 2K1C and control rats were similar in all groups (p > 0.1). The Ca²⁺_i response in the afferent arteriole after 10^-8 M ANG II stimulation was 0.57 ± 0.10, 0.50 ± 0.07, 0.48 ± 0.04 and 0.36 ± 0.05 in the control, sham, non-clipped and clipped kidney, respectively. These data were consistent with the finding of unchanged AT_1aR mRNA levels in AAs from all groups. Although the absolute values were similar, the dose-response curves to ANG II were different. In the control, sham, and non-clipped kidney from 2K1C, the dose-response curve levelled off between 10^-8 and 10^-6 M ANG II. In the clipped kidney, the dose-response curve was linear, with a significantly increased response at 10^-6 M compared to 10^-8 M ANG II (p < 0.05). Inhibition of cyclooxygenase-1 (COX-1) with indomethacin enhanced the ANG II response in the non-clipped ( 0.30 ± 0.09) and clipped ( 0.30 ± 0.09) kidneys from 2K1C (p < 0.005), but not in control rats ( -0.02 ± 0.11, p > 0.8). Conclusively, the ANG II induced Ca²⁺_i response was reduced by COX-1 derived prostaglandins in 2K1C, in contrast to control animals, where the COX-1 inhibition had no effect. COX-2 inhibition with NS-398 did not increase the ANG II mediated Ca²⁺_i response in any of the groups.