CHLORIDE-INDUCED CONTRACTION IN A SKINNED FIBER OF TOAD STRIATED MUSCLE

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  • 松原 三郎
    Department of Physiology, Jikei University School of Medicine
  • 酒井 敏夫
    Department of Physiology, Jikei University School of Medicine
  • 橋爪 孝次
    Department of Physiology, Jikei University School of Medicine

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  • Chloride Induced Contraction in a Skinn

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Cl--induced contraction was studied in a skinned fiber dissected from toad sartorius muscle. When K-methanesulphonate in a relaxing solution was replaced isotonically with KCl, the skinned fiber contracted due to ‘depolarization’-induced Ca++release on the SR. Contraction was induced by superfusing the fiber with solutions containing different concentrations of Cl-. In the presence of 2mM EGTA, the Cl--induced contraction developed when the relaxing solution was replaced by a Crsolution which contained up to 20mM Cl-, while contraction started at 15mM-Cl-in the presence of 0.5mM EGTA. The peak tension of the Cl--induced contraction depended on Clconcentration without obeying the all-or-none law.When the fiber was treated with 1.5mM caffeine, the threshold for the Cl--induced contraction was significantly lowered.<BR>In spite of previous application of Cl- at different concentrations below 80mM, the skinned fiber contracted by sudden increase in Cl-concentration, and the tension versus Cl-concentration curve revealed almost the same shape as that in a fiber equilibrated with Cl--free solution. This suggests that the SR membrane is repolarized after transient depolarization caused by elevation of Cl-concentration.

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