title: Influence of divalent cations on potassium contracture duration in frog muscle fibres.
abstract: Single fibres or small fibre bundles were dissected from twitch muscles of frogs and washed in low Cl-solutions. Contractures were provoked by 122.5 mM K+. At room temperature (17-20 degrees C) the contracture duration was about 1.5 s in the absence of divalent cations and about 3 s in the presence of 2 mM Ca2+. Contractures were prolonged when Ca2+ was replaced by Ni2+ showing that inward Ca current was not the factor responsible for the contracture prolongation. K contracture duration was prolonged in the cold (3 degrees C) by a factor of about 4 in the presence of non-permeating divalent cations (Ni, Co), when 0.1 mM La3+ was applied together with 2 mM Ca2+, and in the virtual absence of divalent cations. The contractures were prolonged in the cold by a factor of 6 or more in the presence of permeant divalent cations (Ca, Sr, Ba, Mg, and Mn at 8 mM). Diffusion of divalent cations in the transverse tubules of the muscle fibres was shown to have a Q10 similar to that in free solution. It was concluded that inward current of divalent cations may shorten contracture duration by causing ionic depletion of the transverse tubules.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D003080:Cold Temperature; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D011898:Ranidae; D013997:Time Factors
chemical_list: D002413:Cations, Divalent; D007473:Ion Channels; D011188:Potassium; D002118:Calcium