Absolute values of myothermic measurements on single muscle fibres from frog.

The heat and force produced in tetanic contraction of single fibres from anterior tibialis muscle of the frog Rana temporaria have been observed at measured temperatures close to 1 and 10 degrees C. Heat was measured using a Hill-Downing type thermopile. In control experiments with a resistor of known heat capacity comparable to a single muscle fibre, it was found that Peltier and Joule heating produced identical thermopile outputs. The Peltier method was used to introduce a known amount of heat into the system in each experiment with a muscle fibre. From the response to this heating the heat capacity of each preparation was obtained and used to calculate the absolute amount of heat production from the thermopile output. The heat produced during tetanic contraction (H) could be described by Aubert's equation [H = Ha (1 - e-t/tau) + hbt]. In some fibres there was no labile heat (Ha), whereas in others it was clearly present. The stable heat rate (hb) was strongly temperature dependent (Q10 = 4.06). At 0 degree C the stable heat rate (normalized by dry weight) in the single fibres was significantly greater than that in whole anterior tibialis muscle.