Post-tetanic potentiation at the neuromuscular junction of the frog.

1. Post-tetanic potentiation (PTP) was studied at the neuromuscular junction of the frog. The magnitude and time course of PTP was dependent on the number of stimuli in the tetanus, rather than on the frequency or duration of the tetanus. At low temperature the maximum amplitude of PTP was unchanged, but the time course was prolonged.2. The magnitude and time course of PTP was accounted for quantitatively by estimated changes in the fraction of transmitter released per stimulus.3. As external [Ca] was reduced, the time for decay of PTP was decreased. The maximum amplitude of PTP, measured with respect to control amplitude at the same [Ca], was unchanged, but occurred at earlier times. The time course of PTP was dependent only on the [Ca] present during the tetanus.4. It is concluded that PTP is associated with an intracellular accumulation of Ca during the tetanus.