Contractile properties, fatiguability and glycolytic metabolism in fast- and slow-twitch rat skeletal muscles of various temperatures.

The influence of muscle temperature (28 and 36 degrees C) on fatiguability and glycolytic metabolism was studied during 5 min of intermittent stimulation of motor nerves of the tibialis anterior, extensor digitorum longus (fast-twitch) and soleus (slow-twitch) muscles in the rat at 100 Hz (200 ms per s). The decline in isometric tension was not affected by muscle temperature either in fast- or in slow-twitch muscles. In fast-twitch muscles the utilization of glycogen during stimulation was the same at 28 and 36 degrees C, while in the soleus muscle it was lower at 28 degrees C. The concentration of glucose-6-phosphate immediately after stimulation was higher in the muscles at 28 degrees C than in those at 36 degrees C, whereas no difference in lactate concentration was found between the two temperature groups. These observations indicate that compared with the rate at 36 degrees C, the rate of glycogenolysis at 28 degrees C is unchanged in fast-twitch, but decreased in slow-twitch muscle. This might imply increased economy of ATP turnover during contraction in the soleus muscle at 28 degrees C.