Nicotinic acid dinucleotide phosphate (NAADP) is a second messenger that produces calcium transients in sea urchin eggs and mammalian and plant cells. Binding of NAADP to its receptor is irreversible, and NAADP responses inactivate. When caged NAADP was released in the localized area of a sea urchin egg, a calcium gradient was produced, which was highest at the site of uncaging. If NAADP levels were then increased globally in the same egg, a calcium gradient that was the inverse of the first was produced, reflecting the gradient of inactivation of the NAADP response. This phenomenon was reversible if the local and global releases of NAADP were separated sufficiently in time, presumably allowing recovery of inactivation. Churchill and Galione propose that the NAADP inactivation, which produces the inversion of the calcium gradient, serves as a spatiotemporal memory of recent calcium transients.
G. C. Churchill, A. Galione, Prolonged inactivation of nicotinic acid adenine dinucleotide phosphate-induced Ca2+ release mediates a spatiotemporal Ca2+ memory. J. Biol. Chem. 276, 11223-11225 (2001). [Abstract] [Full Text]