title: The vesicle cycle in motor nerve endings of the mouse diaphragm.
abstract: Experiments on the mouse diaphragm muscle using intracellular microelectrode recordings and fluorescence microscopy were performed to study the dynamics of transmitter secretion and synaptic vesicle recycling processes (the exocytosis-endocytosis cycle) in motor nerve endings (NE) during prolonged rhythmic stimulation (20 impulses/sec). During stimulation, there were triphasic changes in the amplitude of endplate potentials (EPP): an initial rapid reduction, followed by prolonged (1-2 min) stabilization of amplitude, i.e., a plateau, and then a further slow decrease. Restoration of EPP amplitude after stimulation for 3 min occurred over a period of several seconds. Loading of synaptic vesicles with the fluorescent endocytic stain FM1-43 showed that rhythmic stimulation led to a gradual (over 5-6 min) decrease in NE fluorescence, demonstrating exocytosis of synaptic vesicles. Quantum analysis of the electrophysiological data and comparison of these data with results from fluorescence studies suggested that mouse NE have a high rate of endocytosis and reutilization of synaptic vesicles (the mean recycling time was about 50 sec), which may support the maintenance of reliable synaptic transmission during prolonged high-frequency activity. The sizes of the release-ready and recycling pools of synaptic vesicles were determined quantitatively. It is suggested that vesicle recycling in mouse NE occurs via a short, rapid pathway with incorporation into the recycling pool. Vesicles of the reserve pool are not used for transmitter secretion in the stimulation conditions used here.
authors.affiliation: Kazan State Medical University, 49 Butlerov Street, 420012, Kazan, Russia. zefirova1@rambler.ru
authors.forename: A L
authors.initials: AL
authors.lastname: Zefirov
authors.forename: A V
authors.initials: AV
authors.lastname: Zakharov
authors.forename: R D
authors.initials: RD
authors.lastname: Mukhametzyanov
authors.forename: A M
authors.initials: AM
authors.lastname: Petrov
authors.forename: G F
authors.initials: GF
authors.lastname: Sitdikova
mesh_terms: D000818:Animals; D003964:Diaphragm / Q000293:injuries* / Q000502:physiology*; D004558:Electric Stimulation; D004705:Endocytosis / Q000502:physiology; D066298:In Vitro Techniques; D051379:Mice; D008839:Microelectrodes; D008856:Microscopy, Fluorescence; D017729:Presynaptic Terminals / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D013572:Synaptic Vesicles / Q000502:physiology*