Some effects of nerve stimulation andhemicholinium on quantal transmitter release at the mammalian neuromuscular junction.

1. Rat phrenic nerve-diaphragm preparations have been used to assess some effects of prolonged nerve stimulation on transmitter release.2. The amplitude of the end-plate potentials evoked by prolonged repetitive nerve stimulation fell gradually during stimulation. Most of this fall was due to a reduction in the number of transmitter quanta released by each nerve impulse; however there was also a small reduction in the muscle cell depolarization produced by each quantum of transmitter.3. Repetitive nerve stimulation also produced a small reduction in the amplitude of the miniature end-plate potentials. Recovery of amplitude occurred within about 7-8 min of ceasing stimulation.4. A much greater reduction in miniature end-plate potential amplitude accompanied prolonged nerve stimulation if hemicholinium was present in the bathing solution.5. Estimates of the ;readily available transmitter' (Elmqvist & Quastel, 1965b) were made at intervals following prolonged nerve stimulation. Readily available transmitter was reduced, and recovered over approximately 15 min.6. The relationship of these changes to the changes in nerve terminal synaptic vesicle numbers and volumes induced by similar prolonged nerve stimulation (Jones & Kwanbunbumpen, 1970) is discussed.