During repetitive stimulation of a neuromuscular junction under conditions of low quantal content, end-plate potentials progressively increase in amplitude. This increase is due to an increase in the number of quanta of transmitter released by each nerve impulse. A kinetic analysis of the changes in transmitter release during and following repetitive stimulation suggests that there are four processes that act to increase transmitter release: first and second components of facilitation that decay with time constants of about 50 and 30 msec, augmentation which decays with a time constant of about 7 s, and potentiation which decays with a time constant which ranges from about 30 s to min. These processes are separable on the basis of their kinetic and pharmacological properties. The mechanisms of these processes are not yet known, but some possibilities are briefly discussed in terms of structural, chemical, and statistical factors.
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