Abstract
By using the single sucrose-gap polarization method the relation between membrane potential and contractile tension was analyzed in the frog toe muscle. Two-phase sustained contraction was produced by a prolonged, relatively strong depolarizing pulse. The first phase developed and was inactivated rapidly, while the second phase developed slowly and was maintained during depolarization. Tetrodotoxin in 10-6g/m1 did not suppress either phase of contraction. When the transverse tubules were disrupted by hypertonic glycerol treatment, the sustained contraction was completely abolished. The prolonged hyperpolarizing pulse which was applied shortly before the depolarizing pulse exhibited a marked inhibitory effect on the sustained contraction, especially in the first phase, without causing any noticeable change in the depolarization level. The inhibitory effect depended on the interval between hyperpolarizing and depolarizing pulses and lasted more than 1 min. The nature of the effect of hyperpolarization was analyzed. The well-known suppressing effect of the preceding hyperpolarization on the “creep” phenomenon was confirmed in the toe muscle fibers. It was concluded that hyperpolarization has some direct effect on the excitation-contraction coupling process, especially on the transverse tubular system and the sarcoplasmic reticulum.
