The Influence of Upper Motor Neurones on Excitation-Contraction Coupling in Mammalian Skeletal Muscle

Abstract

Asymmetrical charge movement was recorded in voltage-clamped muscle fibres in rat extensor digitorum longus and soleus fibres. Charge movement was significantly greater and occurred at more positive potentials in extensor digitorum longus fibres than in soleus fibres. A similar difference in voltage-dependence of contraction was recorded in the two types of muscle. There were more indentations in the terminal cisternae of extensor digitorum longus than in soleus fibres. Following spinal cord transection the amount and voltage-dependence of asymmetrical charge movement in soleus fibres became similar to values recorded in extensor digitorum longus. The number of indentations in soleus fibres increased to levels similar to those in extensor digitorum longus fibres. The results strongly support the idea that asymmetrical charge movement is intimately involved in excitation-contraction coupling. Indentations may also have a role in excitation-contraction coupling.