NAADP-induced Ca^2+ release - a new signalling pathway.

Changes in cystosolic Ca^2+ concentration are critical for the regulation of numerous cellular events. Mobilisation of intracellular Ca^2+ stores by Ca^2+ mobilising messengers is a highly conserved mechanism whereby different agonists mediate their cellular effects. NAADP is the newest of these messengers to be described. Accumulating evidence suggests that NAADP targets a novel intracellular Ca2+ release channel that under certain conditions can inactivate prior to opening. These channels are likely located on Ca^2+ stores distinct from the endoplasmic reticulum, the activation of which evokes complex changes in Ca2+ involving cross-talk with other intracellular Ca^2+ channels. Recent demonstrations of changes in cellular NAADP levels by physiologically relevant stimuli establish the importance of this molecule in the control of calcium dynamics.