title: NAADP induces Ca2+ oscillations via a two-pool mechanism by priming IP3- and cADPR-sensitive Ca2+ stores.
abstract: In sea urchin eggs, Ca2+ mobilization by nicotinic acid adenine dinucleotide phosphate (NAADP) potently self-inactivates but paradoxically induces long-term Ca2+ oscillations. We investigated whether NAADP-induced Ca2+ oscillations arise from the recruitment of other Ca2+ release pathways. NAADP, inositol trisphosphate (IP3) and cyclic ADP-ribose (cADPR) all mobilized Ca2+ from internal stores but only NAADP consistently induced Ca2+ oscillations. NAADP-induced Ca2+ oscillations were partially inhibited by heparin or 8-amino-cADPR alone, but eliminated by the presence of both, indicating a requirement for both IP3- and cADPR-dependent Ca2+ release. Thapsigargin completely blocked IP3 and cADPR responses as well as NAADP-induced Ca2+ oscillations, but only reduced the NAADP-mediated Ca2+ transient. Following NAADP-mediated release from this Ca2+ pool, the amount of Ca2+ in the Ca2+-induced Ca2+ release stores was increased. These results support a mechanism in which Ca2+ oscillations are initiated by Ca2+ release from NAADP-sensitive Ca2+ stores (pool 1) and perpetuated through cycles of Ca2+ uptake into and release from Ca2+-induced Ca2+ release stores (pool 2). These results provide the first direct evidence in support of a two-pool model for Ca2+ oscillations.
authors.affiliation: University of Oxford, Department of Pharmacology, Mansfield Road, Oxford OX1 3QT, UK. grant.churchill@pharm.ox.ac.uk
authors.forename: G C
authors.initials: GC
authors.lastname: Churchill
authors.forename: A
authors.initials: A
authors.lastname: Galione
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D036563:Cyclic ADP-Ribose; D005260:Female; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D008954:Models, Biological; D009249:NADP / Q000031:analogs & derivatives / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D009991:Oscillometry; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology; D012617:Sea Urchins; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D009249:NADP; C024376:NAADP; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium