Facilitation is shown to decay as a compound exponential with two
time constants (T1, T2) at both giant and non-giant synapses in squid steilate ganglia
bathed in solutions having low extracellular calcium concentrations ([Ca++]o).
Maximum values of facilitation (F~) were significantly larger, and T1 was significantly
smaller in giant than non-giant synapses. Decreases in [Ca++]o or increases in
[Mn++]o had variable effects on T1 and F1, whereas decreases in temperature
increased T~ but had insignificant effects on/'1. The growth of facilitation during
short trains of equal interval stimuli was adequately predicted by the linear
summation model developed by Mallart and Martin (1967.J. Physiol. (Lond.). 193:
676-694) for frog neuromuscular junctions. This result suggests that the underlying
mechanisms of facilitation are similar in squid and other synapses which release
many transmitter quanta.This work was supported by National Science Foundation research grant GB-36949, National
Research Council (Canada) and Grass Fellowships to Dr. Charlton, and a National Institutes of
Health career award (NS-00070) to Dr. Bittner.Neuroscienc
