Figure 5.

Three modes of nicotinic acid adenine nucleotide diphosphate (NAADP)-mediated Ca²⁺ signaling. (A) NAADP is a local trigger mechanism for detonating global Ca²⁺-induced Ca²⁺-release (CICR) responses from the endoplasmic reticulum (ER). (B) Local Ca²⁺ release by NAADP from acidic stores positioned under the plasma membrane may regulate membrane excitability (excitable cells) or ion fluxes (nonexcitable cells) by modulating Ca²⁺-activated plasma membrane channels. (C) NAADP regulates local cytoplasmic Ca²⁺/pH and luminal Ca²⁺/pH in endolysosomal compartments that may regulate vesicular fusion of late endosomes/lysosomes.