The post-tetanic decay in miniature excitatory junction potential (MEJP) frequency and in facilitation of excitatory junction potentials (EJPs) was measured at crayfish neuromuscular junctions . A 2-s tetanus at 20 Hz caused the MEJP frequency to increase an average of 40 times and the EJP amplitude to increase an average of 13 times . Both MEJP frequency and EJP facilitation decayed with two time constants . The fast component of MEJP frequency decay was 47 ms, and that of EJP facilitation was 130 ms . The slow component of MEJP frequency decay was 0.57 s, and that of EJP facilitation was -1 s . These results were consistent with the predictions of a residual calcium model, with a nonlinear relationship between presynaptic calcium concentration and transmitter release .

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