J Biol Chem, Vol. 275, Issue 12, 8301-8306, March 24, 2000

Nicotinic Acid Adenine Dinucleotide Phosphate-induced Ca²⁺ Release
INTERACTIONS AMONG DISTINCT Ca²⁺ MOBILIZING MECHANISMS IN STARFISH OOCYTES^*

Luigia Santella, Keiichiro Kyozuka^§, Armando A. Genazzani^¶, Laura De Riso, and Ernesto Carafoli^**

From the  Laboratory of Cell Biology Stazione Zoologica "A. Dohrn" Villa Comunale, I-80121, Napoli, Italy, the ^§ Asamushi Marine Biological Station, Asamushi, Aomori 039-3501, Japan, the ^¶ Department of Pharmacology, Tennis Court Road, Cambridge, CB2 1QJ United Kingdom, and the  Department of Biochemistry, University of Padova, 35121 Padova, Italy

An intracellular mechanism activated by nicotinic acid adenine dinucleotide phosphate (NAADP⁺) contributes to intracellular Ca²⁺ release alongside inositol 1,4,5-trisphosphate (Ins-P₃) and ryanodine receptors. The NAADP⁺-sensitive mechanism has been shown to be operative in sea urchin eggs, ascidian eggs, and pancreatic acinar cells. Furthermore, most mammalian cell types can synthesize NAADP⁺, with nicotinic acid and NADP⁺ as precursors. In this contribution, NAADP⁺-induced Ca²⁺ release has been investigated in starfish oocytes. Uncaging of injected NAADP⁺ induced Ca²⁺ mobilization in both immature oocytes and in oocytes matured by the hormone 1-methyladenine (1-MA). The role of extracellular Ca²⁺ in NAADP⁺-induced Ca²⁺ mobilization, which was minor in immature oocytes, was instead essential in mature oocytes. Thus, the NAADP⁺-sensitive Ca²⁺ pool, which is known to be distinct from those sensitive to inositol 1,4,5-trisphosphate or cyclic ADPribose, apparently migrated closer to (or became part of) the plasma membrane during the maturation process. Inhibition of both Ins-P₃ and ryanodine receptors, but not of either alone, substantially inhibited NAADP⁺-induced Ca²⁺ mobilization in both immature and mature oocytes. The data also suggest that NAADP⁺-induced Ca²⁺ mobilization acted as a trigger for Ca²⁺ release via Ins-P₃ and ryanodine receptors.