title: Cyclic adenosine diphosphate ribose activates ryanodine receptors, whereas NAADP activates two-pore domain channels.
abstract: The mechanism by which cyclic adenosine diphosphate ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) mobilize intracellular Ca(2+) stores remains controversial. It is open to question whether cADPR regulates ryanodine receptors (RyRs) directly, as originally proposed, or indirectly by promoting Ca(2+) uptake into the sarco/endoplasmic reticulum by sarco/endoplasmic reticulum Ca(2+)-ATPases. Conversely, although we have proposed that NAADP mobilizes endolysosomal Ca(2+) stores by activating two-pore domain channels (TPCs), others suggest that NAADP directly activates RyRs. We therefore assessed Ca(2+) signals evoked by intracellular dialysis from a patch pipette of cADPR and NAADP into HEK293 cells that stably overexpress either TPC1, TPC2, RyR1, or RyR3. No change in intracellular Ca(2+) concentration was triggered by cADPR in either wild-type HEK293 cells (which are devoid of RyRs) or in cells that stably overexpress TPC1 and TPC2, respectively. By contrast, a marked Ca(2+) transient was triggered by cADPR in HEK293 cells that stably expressed RyR1 and RyR3. The Ca(2+) transient was abolished following depletion of endoplasmic reticulum stores by thapsigargin and block of RyRs by dantrolene but not following depletion of acidic Ca(2+) stores by bafilomycin. By contrast, NAADP failed to evoke a Ca(2+) transient in HEK293 cells that expressed RyR1 or RyR3, but it induced robust Ca(2+) transients in cells that stably overexpressed TPC1 or TPC2 and in a manner that was blocked following depletion of acidic stores by bafilomycin. We conclude that cADPR triggers Ca(2+) release by activating RyRs but not TPCs, whereas NAADP activates TPCs but not RyRs.
authors.affiliation: Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom.
authors.forename: Oluseye A
authors.initials: OA
authors.lastname: Ogunbayo
authors.forename: Yingmin
authors.initials: Y
authors.lastname: Zhu
authors.forename: Daniela
authors.initials: D
authors.lastname: Rossi
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Sorrentino
authors.forename: Jianjie
authors.initials: J
authors.lastname: Ma
authors.forename: Michael X
authors.initials: MX
authors.lastname: Zhu
authors.forename: A Mark
authors.initials: AM
authors.lastname: Evans
mesh_terms: D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D036563:Cyclic ADP-Ribose / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D009249:NADP / Q000031:analogs & derivatives* / Q000235:genetics / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D036563:Cyclic ADP-Ribose; D009249:NADP; C024376:NAADP; D002118:Calcium