Continuous and transient vesicle cycling at a ribbon synapse.
Optical methods were used to study the Ca2+ dependence of vesicle cycling in bipolar cells isolated from goldfish retinas. Uniformly raising the Ca2+ concentration to between 0.8 and 20 microM produced a continuous vesicle cycle of balanced exocytosis and endocytosis with a maximum rate equivalent to the turnover of the entire surface membrane of a terminal every 2 min (or approximately 900 vesicles sec-1). Increasing the Ca2+ concentration above 20 microM inhibited continuous vesicle cycling. In contrast, influx of Ca2+ through voltage-gated channels produced a transient burst of exocytosis that increased the surface area of a terminal by a maximum of 12% (equivalent to the addition of 13,000 vesicles). Endocytosis was delayed until after Ca2+ influx stopped and the average Ca2+ concentration in the terminal declined. Hence, a single terminal has mechanisms for both continuous and transient vesicle cycling.
Rouze
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NC
Department of Pharmacological and Physiological Sciences, The University of Chicago, Chicago, Illinois 60637, USA.
Schwartz
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EA
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004594:Electrophysiology; D004705:Endocytosis / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D005456:Fluorescent Dyes; D006054:Goldfish; D015640:Ion Channel Gating; D007476:Ionophores / Q000494:pharmacology; D008985:Monensin / Q000494:pharmacology; D009475:Neurons, Afferent / Q000502:physiology*; D015737:Nisoldipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D012160:Retina / Q000166:cytology; D013572:Synaptic Vesicles / Q000502:physiology*
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; C092350:FM 4-64; C073804:FM1 43; D005456:Fluorescent Dyes; D007476:Ionophores; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D015737:Nisoldipine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D008985:Monensin; D011188:Potassium; D002118:Calcium