CA2-DINUCLEOTIDE PHOSPHATE IN INTACT SEA-URCHIN EGGS( RELEASE TRIGGERED BY NICOTINATE ADENINE)

Nicotinate adenine dinucleotide phosphate (NAADP) was recently identif ied [Lee and Aarhus (1995) J. Biol. Chem. 270, 2152-2157; Chini, Beers and Dousa (1995) J. Biol. Chem. 270, 3116-3223] as a potent Ca2+-rele asing agent in sea urchin egg homogenates. NAADP triggered Ca2+ releas e by a mechanism that was distinct from inositol 1,4,5-trisphosphate ( InsP(3))- and cyclic ADP-ribose (cADPR)-induced Ca2+ release. When NAA DP was microinjected into intact sea urchin eggs it induced a dose-dep endent increase in cytoplasmic free Ca2+ which was independent of the extracellular [Ca2+]. The Ca2+ waves elicited by microinjections of NA ADP originated at the site of injection and swept across the cytosol. As previously found in sea urchin egg homogenates, NAADP-induced Ca2release in intact eggs was not blocked by heparin or by prior desensit ization to InsP(3) or cADPR. Thio-NADP, a specific inhibitor of the NA ADP-induced Ca2+ release in sea urchin homogenates [Chini, Beers and D ousa (1995) J. Biol. Chem. 270, 3116-3223] blocked NAADP (but not InsP (3) or cADPR) injection-induced Ca2+ release in intact sea urchin eggs . Finally, fertilization of sea urchin eggs abrogated subsequent NAADP -induced Ca2+ release, suggesting that the NAADP-sensitive Ca2+ pool m ay participate in the fertilization response. This study demonstrates that NAADP acts as a selective Ca2+-releasing agonist in intact cells.