title: Ca²⁺ influx slows single synaptic vesicle endocytosis.
abstract: Ca²⁺-dependent synaptic vesicle recycling is critical for maintenance of neurotransmission. However, uncoupling the roles of Ca²⁺ in synaptic vesicle fusion and retrieval has been difficult, as studies probing the role of Ca²⁺ in endocytosis relied on measurements of bulk synaptic vesicle retrieval. Here, to dissect the role of Ca²⁺ in these processes, we used a low signal-to-noise pHluorin-tagged vesicular probe to monitor single synaptic vesicle recycling in rat hippocampal neurons. We show that Ca²⁺ increases synaptic vesicle fusion probability in the classical sense, but surprisingly decreases the rate of synaptic vesicle retrieval. This negative regulation of synaptic vesicle retrieval is blocked by the Ca²⁺ chelator, EGTA, as well as FK506, a specific inhibitor of Ca²⁺-calmodulin-dependent phosphatase calcineurin. The slow time course of aggregate synaptic vesicle retrieval detected during repetitive activity could be explained by a progressive decrease in the rate of synaptic vesicle retrieval during the stimulation train. These results indicate that Ca²⁺ entry during single action potentials slows the pace of subsequent synaptic vesicle recycling.
authors.affiliation: Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9111, USA.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Leitz
authors.forename: Ege T
authors.initials: ET
authors.lastname: Kavalali
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000831:Animals, Newborn; D055592:Biophysical Phenomena / Q000187:drug effects; D001703:Biophysics; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006624:Hippocampus / Q000166:cytology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D018942:Macrolides / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000166:cytology* / Q000187:drug effects; D011336:Probability; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000187:drug effects / Q000502:physiology*; D016559:Tacrolimus / Q000494:pharmacology; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D018942:Macrolides; C493466:Slc17a7 protein, rat; D050598:Vesicular Glutamate Transport Protein 1; C036978:concanamycin A; D002118:Calcium; D016559:Tacrolimus
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