title: Termination of calcium puffs and coupled closings of inositol trisphosphate receptor channels.
abstract: Calcium puffs are localized Ca(2+) signals mediated by Ca(2+) release from the endoplasmic reticulum (ER) through clusters of inositol trisphosphate receptor (IP3R) channels. The recruitment of IP3R channels during puffs depends on Ca(2+)-induced Ca(2+) release, a regenerative process that must be terminated to maintain control of cell signaling and prevent Ca(2+) cytotoxicity. Here, we studied puff termination using total internal reflection microscopy to resolve the gating of individual IP3R channels during puffs in intact SH-SY5Y neuroblastoma cells. We find that the kinetics of IP3R channel closing differ from that expected for independent, stochastic gating, in that multiple channels tend to remain open together longer than predicted from their individual open lifetimes and then close in near-synchrony. This behavior cannot readily be explained by previously proposed termination mechanisms, including Ca(2+)-inhibition of IP3Rs and local depletion of Ca(2+) in the ER lumen. Instead, we postulate that the gating of closely adjacent IP3Rs is coupled, possibly via allosteric interactions, suggesting an important mechanism to ensure robust puff termination in addition to Ca(2+)-inactivation.
authors.affiliation: Department of Neurobiology & Behavior, University of California, Irvine, CA 92697, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Wiltgen
authors.affiliation: Department of Neurobiology & Behavior, University of California, Irvine, CA 92697, USA. Electronic address: dickinsg@uci.edu.
authors.forename: George D
authors.initials: GD
authors.lastname: Dickinson
authors.affiliation: Department of Neurobiology & Behavior, University of California, Irvine, CA 92697, USA.
authors.forename: Divya
authors.initials: D
authors.lastname: Swaminathan
authors.affiliation: Department of Neurobiology & Behavior, University of California, Irvine, CA 92697, USA; Department of Physiology & Biophysics, University of California, Irvine, CA 92697, USA.
authors.forename: Ian
authors.initials: I
authors.lastname: Parker
mesh_terms: D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D005453:Fluorescence; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism*; D007700:Kinetics; D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods*; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology; D014407:Tumor Cells, Cultured
chemical_list: D053496:Inositol 1,4,5-Trisphosphate Receptors; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium
keywords: Calcium; Coupled gating; Inositol 1,4,5-trisphosphate receptors; Puffs; TIRF microscopy