Contractile properties of fast and slow twitch muscles of the rat at temperatures between 6 and 42 degrees C.

The effect of a wide range of temperature on the development of twitch and tetanic tension was investigated in directly stimulated rat fast (EDL) and slow (SOL) twitch muscle preparations. When increasing the temperature from 6 to 30 degrees C the maximum tetanic tension rose steadily. The Q10 was 2.3 (EDL) and 2.7 (SOL) for temperatures between 12 and 22 degrees C. The twitch tension output of SOL muscle increased up to 36-38 degrees C, whereas the EDL muscle exhibited a distinct maximum at 22 degrees C followed by a 50% decrease at 34 degrees C. Post-tetanic potentiation was observed in EDL muscle at temperatures higher than 20 degrees C. In SOL muscle neither posttetanic potentiation nor cold potentiation could be observed. The twitch/tetanus ratio was 0.2-0.3 at 35 degrees C but 0.7-0.8 at 6 degrees C. In both muscle types the most characteristic effect of temperature was the prolongation of the time to peak and the relaxation time in parallel to cooling. The tension rise of fast twitch rat muscle during cooling from 35 degrees C downwards can be compared to the cold potentiation of frog sartorius muscle. It is suggested that the main effect of temperature on muscle function concerns the process of Ca2+ release and of Ca2+ uptake. The different response of SOL muscle may be related to the less developed sarcoplasmic reticulum and the lower Ca2+ ATPase activity.