Mobility and turnover of vesicles at the synaptic ribbon.
Ribbon synapses release neurotransmitter continuously at high rates, and the ribbons tether a large pool of synaptic vesicles. To determine whether the tethered vesicles are actually released, we tracked vesicles labeled with styryl dye in mouse retinal bipolar cell terminals whose ribbons had been labeled with a fluorescent peptide. We photobleached vesicles in regions with ribbons and without them and then followed recovery of fluorescence as bleached regions were repopulated by labeled vesicles. In the resting terminal, fluorescence recovered by approximately 50% in non-ribbon regions but by only approximately 20% at ribbons. Thus, at rest, vesicles associated with ribbons cannot exchange freely with cytoplasmic vesicles. Depolarization stimulated vesicle turnover at ribbons as bleached, immobile vesicles were released by exocytosis and were then replaced by fluorescent vesicles from the cytoplasm, producing an additional increase in fluorescence specifically at the ribbon location. We conclude that vesicles immobilized at synaptic ribbons participate in the readily releasable pool that is tapped rapidly during depolarization.
LoGiudice
Lisamarie
L
Department of Neurobiology and Behavior, State University of New York, Stony Brook, Stony Brook, New York 11794-5230, USA.
Sterling
Peter
P
Matthews
Gary
G
D000429:Alcohol Oxidoreductases; D000818:Animals; D056970:Co-Repressor Proteins; D004268:DNA-Binding Proteins / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal / Q000379:methods; D008854:Microscopy, Electron / Q000379:methods; D018408:Patch-Clamp Techniques / Q000379:methods; D010750:Phosphoproteins / Q000378:metabolism; D038761:Photobleaching; D011189:Potassium Chloride / Q000494:pharmacology; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012160:Retina / Q000166:cytology; D051245:Retinal Bipolar Cells / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013572:Synaptic Vesicles / Q000502:physiology* / Q000648:ultrastructure
D056970:Co-Repressor Proteins; D004268:DNA-Binding Proteins; C092350:FM 4-64; D010750:Phosphoproteins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D011189:Potassium Chloride; D000429:Alcohol Oxidoreductases; C111341:Ctbp2 protein, mouse