title: Synaptotagmin 1 is required for vesicular Ca²⁺/H⁺-antiport activity.
abstract: A low-affinity Ca²⁺/H⁺-antiport was described in the membrane of mammalian brain synaptic vesicles. Electrophysiological studies showed that this antiport contributes to the extreme brevity of excitation-release coupling in rapid synapses. Synaptotagmin-1, a vesicular protein interacting with membranes upon low-affinity Ca²⁺-binding, plays a major role in excitation-release coupling, by synchronizing calcium entry with fast neurotransmitter release. Here, we report that synaptotagmin-1 is necessary for expression of the vesicular Ca²⁺/H⁺-antiport. We measured Ca²⁺/H⁺-antiport activity in vesicles and granules of pheochromocytoma PC12 cells by three methods: (i) Ca²⁺-induced dissipation of the vesicular H⁺-gradient; (ii) bafilomycin-sensitive calcium accumulation and (iii) pH-jump-induced calcium accumulation. The results were congruent and highly significant: Ca²⁺/H⁺-antiport activity is detectable only in acidic organelles expressing functional synaptotagmin-1. In contrast, synaptotagmin-1-deficient cells--and cells where transgenically encoded synaptotagmin-1 was acutely photo-inactivated--were devoid of any Ca²⁺/H⁺-antiport activity. Therefore, in addition to its previously described functions, synaptotagmin-1 is involved in a rapid vesicular Ca²⁺ sequestration through a Ca²⁺/H⁺ antiport.
authors.affiliation: Neurosciences Fondamentales, Faculté de Médecine, Université de Genève, Genève, Switzerland.
authors.forename: Joao Miguel
authors.initials: JM
authors.lastname: Cordeiro
authors.forename: Bernadett
authors.initials: B
authors.lastname: Boda
authors.forename: Paula P
authors.initials: PP
authors.lastname: Gonçalves
authors.forename: Yves
authors.initials: Y
authors.lastname: Dunant
mesh_terms: D017920:Antiporters / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001923:Brain Chemistry / Q000187:drug effects; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002999:Clone Cells; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D005456:Fluorescent Dyes; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin / Q000494:pharmacology; D018942:Macrolides / Q000494:pharmacology; D016716:PC12 Cells; D017933:Peripheral Nervous System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism; D050863:Synaptotagmin I / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D050987:Vesicle-Associated Membrane Protein 1 / Q000037:antagonists & inhibitors / Q000276:immunology
chemical_list: D017920:Antiporters; D027682:Cation Transport Proteins; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D018942:Macrolides; D050863:Synaptotagmin I; D050987:Vesicle-Associated Membrane Protein 1; C027614:calcium-hydrogen antiporters; C057620:bafilomycin A; D015759:Ionomycin; D006859:Hydrogen; D002118:Calcium