Figure 5. Ca²⁺- and pH-dependence of the NAADP-induced Ca²⁺ release.

(A) Extravesicular free Ca²⁺ concentration-dependence of the IP₃-, cADPR- and NAADP-mediated system in passively loaded liver microsomes. Extravesicular pCa (4–8) was set by EGTA (200–750 μM), NAADP (■), IP₃ (◆) and cADPR (□) were applied at supramaximal concentrations (10 μM). (B) Differential effect of pH on the cADPR- and NAADP-sensitive Ca²⁺-releasing system. The pH of the Ca²⁺-release medium was changed from 6.4 to 7.8, and the amount of ⁴⁵Ca²⁺ released by 10 μM cADPR (□) and 10 μM NAADP (■) was determined.