Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent Ca2+ mobilizing endogenous compound
known to date. Although its Ca2+releasing activity has been demonstrated in many cell types and in response to different
extracellular stimuli, several aspects of NAADP signaling are unclear.
This overview focuses on the controversial aspects and reviews NAADP´s role as second messenger: endogenous concentrations
and its receptor-mediated alterations, metabolism, and potential organelle and ion channel targets. Finally, the role
of NAADP as Ca2+ trigger is discussed by reviewing the development of local into global Ca2+ signals evoked by