Development of the electromechanical link in skeletal muscle fibers during postnatal ontogenesis of albino rats

Abstract

1. The development of the electromechanical link in skeletal muscle fibers of rats during postnatal ontogenesis has been studied by producing potassium contractures. 2. All muscles investigated were capable of producing a stable contracture during the first week after birth. This ability then diminishes, more rapidly in some muscles than in others. The fast tibialis anterior loses this ability by the 12–13th day. In the slow soleus the contracture becomes unstable and the muscle relaxes despite continuing depolorization by excess of potassium ions. 3. From the data obtained, the decrease in ability to produce a contracture can be interpreted as the results of an increase in functional lability of the electromechanical link during postnatal ontogenesis. 4. It may be supposed that the increase in functional lability of the electromechanical link is an important component of evolution of the contractile function of skeletal muscles; it can be observed not only during individual development but also in the course of phylogenesis.