[Mechanisms of transmitting excitation in the electromechanical connections system of frog phasic muscle fibers].

The effect of replacement of Na ions by isomorphic Li ions on the dynamic parameters of isometric contractions and the distribution of Na, K, and Li in the frog m. sartorius involved increase of the muscle maximum tension during first 10-15 min. A possible role of Na and Li ions in the muscle contraction is discussed with regard to the assumption of a mechanism of participation of Na ions in the transmission of excitation from the plasmic membrane to the sarcoplasmic reticulum membrane.