The effect of calcium ions and temperature on the binomial parameters that control acetylcholine release by a nerve impulse at amphibian neuromuscular synapses.

1. A study has been made of the effects of changing the external calcium concentration, Ca, and the temperature on both the number of quanta available for release by the nerve impulse (n) as well as the increase in release probability of a quantum p(t) during the release period (from 0 to T) following a nerve impulse at synapses in amphibian striated muscle.2. When Ca was increased in the low range from 0.25 to 0.4 mM at 18 degrees C, the average quantal content of the e.p.p. (m) increased as the fourth power of Ca and this was primarily due to a third power dependence of n on Ca; the dissociation constants and power dependence of n on calcium determined in the Ca range from 0.25 to 1.0 mM were successfully used to predict the changes in size of the e.p.p. in the very high Ca range from 1 to 10 mM. When the temperature was increased from 7 to 18 degrees C in a Ca of 0.6 mM or 0.35 mM, n increased with a Q(10) of 2.5.3. When Ca was increased in the range from 0.25 to 1.0 mM at 18 degrees C, the probability that a quantum initially available for release is released during the release period (p(T)) was very sensitive to Ca, increasing as the third power of Ca and with a dissociation constant of 0.13 mM. When the temperature was increased from 7 to 18 degrees C in a Ca of 0.6 mM or 0.35 mM, p(T) decreased.4. The histograms of latencies of individual quanta following a nerve impulse was very temperature dependent: the time to peak of the histograms (i.e. the interval in which most quanta fell) had a Q(10) of over 4 as did the time constant of decline of the histograms in the temperature range from 7 to 18 degrees C.5. The average number of quanta released up to time t during the release period following a nerve impulse, namely np(t), was well described by a stochastic process in which p(t) was determined by two reactions; one of these reactions released available quanta from the nerve terminal whilst the other made some of the available quanta unavailable for release by the nerve impulse.