Thermal acclimation, neuromuscular synaptic delay and miniature end-plate current decay in the frog Rana temporaria

1. The effects of 1 or 2­3 weeks of acclimation to 4 °C and 24 °C of overwintering grass frogs (Rana temporaria) on the synaptic delay and on the time constant of the decay phase (tau) of miniature end-plate currents (MEPCs) in the neuromuscular junction of sartorius muscle were studied. In order to equalize the possible effects of differential starvation, the animals were usually cross-acclimated to the two temperatures. 2. Synaptic delay was not affected by temperature acclimation but was slightly prolonged by the more profound starvation at the higher temperature when the cross-acclimation procedure was not used. The average Q10 of synaptic delay between 4 and 24 °C was 2.60 and of minimum synaptic delays, 2.64. The corresponding values for apparent activation energy (Ea) were 65.79 and 66.48 kJ mol-1. 3. The time constant of the decay phase of MEPCs was not affected by temperature acclimation. The average Q10 between 4 and 24 °C was 2.27. The corresponding Ea value was 56.02 kJ mol-1. 4. The function of peripheral neuromuscular synapses is well regulated and changes in its time relationships do not appear to be involved in the thermal acclimation of frogs.