ADP-ribosyl cyclase (ARC) produces a Ca²⁺-mobilizing second messenger, cyclic ADP-ribose (cADPR), from NAD. In this study, we purified an ARC from rat kidney, which was identified as the β1 subunit of Na, K-ATPase (Atp1b1). Recombinant Atp1b1 exhibited ARC activity and generated cADPR. Knockdown of Atp1b1 in mouse mesangial cells (MES-13) inhibited angiotensin II (AngII)-induced cADPR synthesis and the subsequent long-lasting Ca²⁺ signals. These findings demonstrate that Atp1b1 is coupled with the AngII receptor and is activated to produce cADPR, thereby mediating Ca²⁺ signaling in the kidney.