UNIQUE INACTIVATION PROPERTIES OF NAADP-SENSITIVE CA2+ RELEASE

Ca2+ mobilization from intracellular stores constitutes an important m echanism for generating cytoplasmic Ca2+ signals. Inositol trisphospha te (InsP(3)) and ryanodine receptors are the two families of intracell ular Ca2+ release channels that have been identified, which may be reg ulated by separate intracellular messengers, InsP(3) and cyclic adenos ine 5'-diphosphate ribose, respectively. A third molecule, nicotinic a cid adenine dinucleotide phosphate (NAADP), has recently been recogniz ed as a potent Ca2+ releasing agent in sea urchin eggs and microsomes. We now report that non-releasing concentrations of NAADP fully and ir reversibly inactivate the NAADP-sensitive Ca2+ release mechanism. This phenomenon occurred both in intact sea urchin eggs and in homogenates and is not shared by either InsP(3) or cyclic adenosine 5'-diphosphat e ribose, The novel properties of this Ca2+ release mechanism, giving a one-shot Ca2+ release, may be suited to irreversible cellular events .