NICOTINIC ACID-ADENINE DINUCLEOTIDE PHOSPHATE MOBILIZES CA2-INSENSITIVE POOL( FROM A THAPSIGARGIN)

Nicotinic acid-adenine dinucleotide phosphate (NAADP) is a novel intra cellular Ca2+ releasing agent recently described in sea-urchin eggs an d egg homogenates. Ca2+ release by NAADP is independent of that induce d by either inositol trisphosphate (InsP(3)) or cyclic adenosine dinuc leotide phosphate (cADPR). We now report that in sea urchin egg homoge nates, NAADP releases Ca2+ from a Ca2+ pool that is distinct from thos e that are sensitive to InsP(3) and cADPR. This organelle has distinct Ca2+ uptake characteristics: it is insensitive to thapsigargin and cy clopiazoic acid, but maintenance of the pool shows some requirement fo r ATP. Although the different Ca2+ pools have different characteristic s, there appears to be some degree of overlap or cross-talk between th e NAADP- and cADPR/InsP(3)-sensitive Ca2+ pools. Ca2+-induced Ca2+ rel ease is unlikely to account for the apparent overlap between stores, s ince NAADP-induced Ca2+ release, in contrast with that stimulated by c ADPR, is not potentiated by bivalent cations.