[Effects of divalent cations on the muscle spindle of frogs].
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 approximately 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.
D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009470:Muscle Spindles / Q000187:drug effects*; D009431:Neural Conduction / Q000187:drug effects; D011892:Rana catesbeiana
D002413:Cations, Divalent; D008345:Manganese; D008274:Magnesium; D002118:Calcium