Fig. 1.

NAADP-mediated Ca²⁺ signalling. Schematic depicting selected NAADP-linked stimuli (left) and NAADP-regulated Ca²⁺-dependent cellular responses (right). The intervening diagram summarizes the “trigger” hypothesis for NAADP action, whereby NAADP produced in response to cellular stimulation activates NAADP-sensitive Ca²⁺ channels located on acidic Ca²⁺ stores. The resulting local Ca²⁺ signal is then amplified by neighbouring IP₃ and ryanodine receptors on the ER by Ca²⁺-induced Ca²⁺ release (CICR) to mediate a larger global Ca²⁺ signal.