title: Continuous vesicle cycling in the synaptic terminal of retinal bipolar cells.
abstract: Endocytosis and exocytosis were investigated in the synaptic terminal of retinal bipolar cells by monitoring the uptake and loss of the fluorescent dye FM1-43. Depolarization in the presence of Ca2+ stimulated a continuous cycle of exocytosis and endocytosis that was approximately balanced at rates up to 3800 vesicles per s. Vesicles became available for exocytosis within 1 min of endocytosis, and about 700,000 releasable vesicles were specifically localized to a region within 2 microm of the plasma membrane. Release of caged Ca2+ using NP-EGTA while simultaneously monitoring cytosolic Ca2+ with Fura-2 indicated that continuous exocytosis was stimulated by sub-micromolar levels of Ca2+. It has been suggested that the ribbon synapse of bipolar cells only supports transient exocytosis, but our results demonstrate that this synapse is specialized for the continuous secretion of neurotransmitter.
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge, United Kingdom.
authors.forename: L
authors.initials: L
authors.lastname: Lagnado
authors.forename: A
authors.initials: A
authors.lastname: Gomis
authors.forename: C
authors.initials: C
authors.lastname: Job
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D004594:Electrophysiology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D005456:Fluorescent Dyes; D006054:Goldfish; D008564:Membrane Potentials / Q000502:physiology; D009475:Neurons, Afferent / Q000166:cytology / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000378:metabolism; D017729:Presynaptic Terminals / Q000502:physiology*; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D012160:Retina / Q000166:cytology*; D013572:Synaptic Vesicles / Q000502:physiology*
chemical_list: C073804:FM1 43; D005456:Fluorescent Dyes; D018377:Neurotransmitter Agents; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D002118:Calcium