The temperature dependence of isometric contractions of single, intact fibres dissected from a mouse foot muscle.

1. Isometric tension responses to electrical stimulation have been studied at 7.5 37.5 degrees C in single, intact fibres of the flexor digitorum brevis muscle of the mouse. A large number of reproducible tetani could be obtained at temperatures less than or equal to 35 degrees C. 2. The tetanic force per cross-sectional area generated at 25.0 degrees C was 375 +/- 56 kPa (mean +/- S.D., n = 16). 3. The curve relating maximum tetanic tension to temperature exhibited a transition between a level of almost unaltered force (25.0-32.5 degrees C) and a marked force decline (less than or equal to 20.0 degrees C). At temperatures higher than 35.0 degrees C force production was markedly depressed and this reduction was in some cases irreversible. 4. Twitch tension showed less regular dependence on temperature; it was reduced less than tetanic tension at low temperatures. Thus, the twitch/tetanus tension ratio was higher at low temperatures. 5. The times for twitch contraction and for twitch half-relaxation (i) ranged from 7 to 14 ms and from 6 to 15 ms at 35.0 degrees C and (ii) exhibited Q10 values of 3.2 +/- 0.4 and 4.0 +/- 0.6, respectively. 6. It is concluded that it is possible to use intact, single fibres dissected from mammalian skeletal muscle in physiological studies. Our results are close to previous results obtained from mammalian muscles except that the tetanic tension per cross-sectional area was found to be higher than commonly reported.