Temperature dependence of spontaneous quantal and nonquantal transmitter release from motor nerve endings in the mouse

Abstract

Spontaneous quantal and nonquantal acetylcholine release were investigated at an ambient temperature range of 10–35°C in a preparation of white mouse hemidiaphragm. Quantal transmitter release was assessed by the frequency of miniature endplate potentials and nonquantal secretion by the level of H-effect. Spontaneous quantal release rose exponentially in step with increasing temperature. Two relative maxima, one of 20°C and the other of 35°C were noted in the temperature dependence of nonquantal transmitter release. Nonquantal release of acetylcholine did not take place at a temperature of 10°C. The effective energy of activation of quantal release was calculated as 57.0 kJ/mole over the temperature range investigated; that of the nonquantal release process at intervals of 15–20°C and 25–35°C measured 45.5 and 38.2 kJ/mole respectively. It is suggested that an active transport system process rather than simple diffusion of acetylcholine molecules is responsible for nonquantal release of this neurotransmitter.