THERMAL-ACCLIMATION, NEUROMUSCULAR SYNAPTIC DELAY AND MINIATURE END-PLATE CURRENT DECAY IN THE FROG RANA-TEMPORARIA

1. The effects of 1 or 2-3 weeks of acclimation to 4 degrees C and 24 degrees C of overwintering grass frogs (Rana temporaria) on the synapt ic 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 dif ferential starvation, the animals were usually cross-acclimated to the two temperatures. 2. Synaptic delay was not affected by temperature a cclimation but was slightly prolonged by the more profound starvation at the higher temperature when the cross-acclimation procedure was not used. The average Q(10) of synaptic delay between 4 and 24 degrees C was 2.60 and of minimum synaptic delays, 2.64. The corresponding value s for apparent activation energy (E(a)) were 65.79 and 66.48 kJmol-(1) 3. The time constant of the decay phase of MEPCs was not affected by temperature acclimation. The average Q(10) between 4 and 24 degrees C was 2.27. The corresponding E(a) value was 56.02kJmol(-1). 4. The func tion of peripheral neuromuscular synapses is well regulated and change s in its time relationships do not appear to be involved in the therma l acclimation of frogs.