Isometric twitch and tetanic contraction of frog skeletal muscles at temperatures between 0 to 30 degrees C.

Maximum twitch and tetanic tension development, time to peak, and half relaxation time were studied on isolated frog sartorius muscles stimulated directly in Ringer's solution at different temperatures. Cooling from 20 degrees C to 10 degrees C decreased the tetanic tension (Q10 = 1.3-1.4). At temperatures above 25 (30) degrees C the tension output was reduced. The response to cooling of the twitch contraction was a prolongation of the time to peak (Q10 = 2.4) and of the relaxation time (Q10 = 2.7) independently of the amplitude which increased in most muscles. Between 20 and 10 degrees C the tension output rose by a factor of 1.2-1.3. The failure of this response showed no relation to season. The increase of the twitch tension but the decrease of tetanic tension in parallel with the temperature drop shifted the ratio twitch/tetanus to higher values (0.5 to 0.8). The results suggest that cooling effects both the Ca2+ release and and the Ca2+ re-uptake but the latter one with a higher Q10. This causes a prolongation of the active state and a cold potentiation if further facilitating conditions are present. In contrast, the response to temperature of the tetanic tension seems to be due to the temperature dependent force generation per cross-bridge.