Die abfallende Phase des aktiven Zustandes des Tibialis anterior, Gastrocnemius und Soleus der Katze und ihre Beeinflussung durch Dehnung und Sympathicomimetica

Summary

The time course of the active state curve has been studied in the tibialis anterior, gastrocnemius, and soleus muscles of the cat. The technique employed was the method of quick release described by Hill (1953), Ritchie (1954), and Ritchie and Wilkie (1955).

The rate of relaxation of the contractile elements was higher in the fast-contracting tibialis anterior and gastrocnemius muscles than in the slow-contracting soleus muscle. The active state of the tibialis anterior, gastrocnemius, and soleus muscle ended at about 90 msec, 100 msec, and 210 msec respectively after a single stimulus. The duration of the active state was prolonged by a stretch applied to the muscles prior to stimulation.

Adrenaline reduced the rate of relaxation of the contractile elements in the tibialis anterior muscle and increased that of the soleus muscle. This effect was diminished by stretch of the muscles. Isoprenaline exerted a similar effect on the duration of the active state as did adrenaline, whereas noradrenaline proved to be much less potent in influencing the rate of relaxation.

It is therefore concluded that the difference in fusion frequency of fast- and slow-contracting muscles of the cat is due to a different time course of relaxation of the contractile elements. The changes in tension development in the soleus and tibialis anterior muscles following administration of adrenaline, noradrenaline, and isoprenaline result from a reduced (soleus) or an increased (tibialis anterior) duration of the active state.