NAADP: An emerging calcium signaling molecule.

Cells possess multiple Ca(2+) stores and multiple messengers for mobilizing them. In addition to inositol trisphosphate and cyclic ADP-ribose, nicotinic acid adenine dinucleotide phosphate (NAADP), a metabolite of NADP, is shown to be a potent Ca(2+) signaling molecule in both invertebrate and mammalian cells. This article summarizes the recent results of this newly discovered Ca(2+) signaling mechanism and explores the implications of the apparent proliferation of Ca(2+) messengers.