Optical monitoring of transmitter release and synaptic vesicle recycling at the frog neuromuscular junction

摘要: 1. Frog cutaneous pectoris motor nerve terminals were loaded with the fluorescent dye FM1-43, which produced a series of discrete spots along length terminals, each spot evidently marking cluster synaptic vesicles. Terminals imaged for 2-10 min as they destained during repetitive stimulation. Endplate potentials (EPPs) recorded simultaneously from muscle fibres innervated by these terminals; their summed amplitudes provided measure cumulative transmitter release. 2. Individual in any one terminal varied initial brightness but at similar fractional rates. 3. The rates release and destaining increased stimulus frequency range 2-30 Hz. At 40 Hz, however, both slower than 30 4. In twenty-six experiments, loss compared quantitatively. When time course EPPs was scaled to fit first 30-60 s destaining, two curves usually diverged later times, curve falling below EPP curve. Thus, assuming that are proportional early times rate decreases relative 5. frequencies 2 results could be fitted simple model vesicles lose exocytosis and, after fixed recycle 'dead time', re-enter vesicle pool, mixing randomly other 6. Unlike stimulation lower frequencies, Hz amplitude did not significantly diverge. Stimulation periods lasted up about min. Interpreted according recycling, this suggests recycling is inhibited 7. led predictions number, N, (labelled unlabelled) calculated value N decreased less then increased, reflecting appearance recycled pool. 8. From estimates amplitudes, fraction released per shock, F, entire period. low (2-5 Hz), an rapid fall, F slowly monotonically 50% 6 higher different process observed.(ABSTRACT TRUNCATED AT 400 WORDS)