Although a dysfunction of the calcium metabolism occurs in diabetes mellitus, alterations of Ca<sup>2+</sup> uptake induced by angiotensin II (ANG II) in renal proximal tubular cells (PTCs) grown in high-glucose medium are not fully elucidated. Thus, we examined whether high glucose concentrations can induce an alteration of the ANG II effect on the Ca<sup>2+</sup> uptake and its action mechanism in primary cultured renal PTCs. PTCs were exposed to different glucose concentrations (5–100 m M) and time intervals (0–48 h). There was a sustained increase of Ca<sup>2+</sup> uptake at glucose concentrations >15 m M. Thus, we selected 25 m M glucose and incubation for 48 h to maintain a hyperglycemic condition in vitro, unlike short-time regulatin. ANG II significantly inhibited the Ca<sup>2+</sup> uptake in a dose-dependent manner in a 5-m M glucose medium. In addition, downregulation of ANG II receptors appeared in a glucose dose dependent manner. However, PTCs treated with 25 m M glucose for 48 h, not 12 h, did not exhibit the inhibitory effect of ANG II (10<sup>–7</sup> M) on Ca<sup>2+</sup> uptake, although the inhibitory effect of ANG II on Ca<sup>2+</sup> uptake occurred in the presence of 25 m M mannitol or L-glucose. Staurosporine, bisindolylmaleimide I (protein kinase C, PKC, inhibitors), 12- o-tetradecanoylphorbol 13-acetate pretreatment, SQ 22536 (an adenylate cyclase inhibitor), and myristoylated protein kinase A inhibitor amide 14–22 (a protein kinase A inhibitor) blocked the 25-m M-glucose-induced alteration of ANG II effect on Ca<sup>2+</sup> uptake. These results suggest that both PKC and cyclic adenosine monophosphate (cAMP) pathways are involved in the high-glucose-induced alteration of ANG II effect on Ca<sup>2+</sup> uptake. Indeed, 25 m M glucose increased PKC activity and cAMP contents. In conclusion, a high glucose concentration altered ANG II induced inhibition of Ca<sup>2+</sup> uptake via PKC and cAMP pathways in the PTCs.