Temperature effects on spontaneous and evoked quantal size at the frog neuromuscular junction

The amplitudes, time integrals, and half-decay times of miniature endplate currents (MEPCs) and of endplate currents (EPCs) were measured in preparations in low Ca2+-high Mg2+ Ringer, in which the probability of the evoked release of more than one quantum was low. The measurements were made at 5 to 7, 11, and 15 degrees C. There is no consistent difference in these properties of evoked and spontaneously released quanta at any of the temperatures. I. S. Cohen and W. Van der Kloot ((1983) J. Physiol. (Lond.) 336: 335-344) compared the effects of temperature changes on MEPCs and on the endplate currents evoked by set amounts of iontophoretically applied ACh. The results suggested that the quantity of ACh/quantum was relatively unaffected by changes in temperature. This conclusion can now be extended to quanta released by nerve stimulation.