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Activation of the contractile apparatus of skinned fibres of frog by the divalent cations barium, cadmium and nickel.
Author(s) -
Stephenson D G,
Thieleczek R
Publication year - 1986
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1986.sp016273
Subject(s) - divalent , chemistry , barium , biophysics , ionic strength , contraction (grammar) , ionic radius , cadmium , ionic bonding , calcium , ion , analytical chemistry (journal) , inorganic chemistry , chromatography , aqueous solution , medicine , organic chemistry , biology
The contractile apparatus of mechanically skinned muscle fibres of frog can be reversibly activated by Ba2+ and Cd2+. The maximum force induced by both Ba2+ and Cd2+ is the same as that induced by Ca2+ and Sr2+. The ionic concentrations of the divalent cations required to induce 50% of the maximum activated force at 1 mM‐Mg2+, pH 7.10, 22 degrees C and 250 mM ionic strength are about 8 X 10(‐7) M for Ca2+, 5 X 10(‐6) M for Cd2+, 2.6 X 10(‐5) M for Sr2+ and 7 X 10(‐4) M for Ba2+. Exposure of the skinned fibre to relatively low Ni2+ concentrations (between 10(‐6) and 10(‐5) M) resulted in a transient force response accompanied by an irreversible change in the ability of the preparation to develop force. The Ba2+‐ and Cd2+‐activation curves are considerably flatter than the corresponding curves for Ca2+ and Sr2+. An increase in Mg2+ concentration from 1 to 3 mM decreased the sensitivity of the contractile apparatus to Ba2+ by a factor of about 1.5 without affecting the maximum force response. The Ca2+‐activation curve was modified in the presence of subthreshold concentrations of Ba2+ and the results indicate that Ba2+ could have both an activating and an inhibitory action on the Ca2+‐activated force. A kinetic model which can quantitatively explain the results for activation of contraction by Ba2+ and Ca2+, is described.