Action of divalent cations on the muscle spindle of the frog

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  • KONTANI Hitoshi
    Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University
  • KUDO Yoshihisa
    Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University
  • FUKUDA Hideomi
    Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University

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Other Title
  • カエル筋紡錘に対する２価陽イオンの作用
  • カエル キン ボウスイ ニ タイスル 2カ ヨウイオン ノ サヨウ

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Abstract

Afferent discharges were recorded in the nerve from the isolated muscle spindle of the m. extensor longus digiti IV of the bullfrog. Discharges of about 10 Hz generated by a sustained stretch were reduced concentration-dependently when Ca2+, Mg2+ or Mn2+ (1.0 ?? 8.0 mM) was added to normal Ringer's solution containing 2.0 mM Ca2+. In terms of the decrease of discharges following the addition of Ca2+ or Mn2+ (4.0 mM), abortive spikes were observed. With an excess of Mg2+ (4.0 mM), abortive spikes were not apparent. Removal of Ca2+ from the Ringer's solution caused an increase in the rate of discharges, and normal levels were restored by the addition of Ca2+ (2.0 mM), Mg2+ (2.3 mM) or Mn2+ (1.8 mM). Application of much higher concentrations of these ions to the nerve trunk produced no alterations in the conduction of afferent discharges. It appears that Ca2+ in the external medium contributes to the inhibition of the mechanism responsible for generating afferent discharges in the muscle spindle and that Ca2+ action is not specific since Mg2+ and Mn2+ can act as substitutes for Ca2+ to regulate afferent discharges.

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