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Ca2+ sensitizing effects of EMD 53998 after troponin replacement in skinned fibres from porcine atria and ventricles

  • Original Article
  • Molecular and Cellular Physiology
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Abstract

Skinned fibres from porcine ventricles exhibited a higher Ca2+ sensitivity (pCa50, i.e. -log10 Ca2+ concentration required for half-maximal activation, for force generation) than atrial fibres. The thiadiazinone derivative EMD 53998 increased Ca2+ sensitivity and Ca2+ efficacy in both preparations. The drug effect depended on the isoform of troponin (Tn). Using the vanadate method TnI and TnC could be partly extracted and replaced by foreign tropin or by the TnI subunit of added foreign troponins. We investigated the relationship between pCa and force development before and after replacement of TnI with foreign troponin (bovine ventricular troponin, cTn, or rabbit skeletal muscle troponin, sTn) in the presence and absence of EMD 53998. Substitution with bovine cTn increased Ca2+ sensitivity to a value characteristic of bovine ventricular skinned fibres (pCa50=5.4) and was further increased by EMD 53998. Substitution with sTn also increased Ca2+ sensitivity, but subsequent addition of EMD 53998 caused little further increase in Ca2+ sensitivity. Following extraction of TnI with vanadate, skinned fibres contracted in a Ca2+-independent manner and failed to relax at a pCa of 8. Relaxation could be induced, however, by bovine ventricular TnI and rabbit skeletal muscle recombinant TnI. This relaxation could be reversed by EMD 53998 (100 μM). The Ca2+-independent force of contracted fibres could also be depressed by a TnI inhibitory peptide, (cTnI 137–148) and, in addition, this effect was antagonized by EMD 53998. These results suggest that EMD 53998 antagonizes the inhibitory action of TnI, possibly by interfering with the interaction of the TnI inhibitory region with actin.

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Author notes

  1. John D. Strauss

    Present address: Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Va., USA

  2. Jennifer Van Eyk

    Present address: Department of Biochemistry and MRC Group Protein Structure and Function, University of Alberta, Edmonton, Alberta, Canada

Authors and Affiliations

  1. Department of Physiology II, University of Heidelberg, Im Neuenheimer Feld 326, D-691620, Heidelberg, Germany

    Zacharias Barth, John D. Strauss, Susanne Heyder, Jennifer Van Eyk, Rudolf J. Wiesner & J. Caspar Rüegg

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  1. Zacharias Barth
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  6. J. Caspar Rüegg
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Barth, Z., Strauss, J.D., Heyder, S. et al. Ca2+ sensitizing effects of EMD 53998 after troponin replacement in skinned fibres from porcine atria and ventricles. Pflügers Arch. 430, 220–229 (1995). https://doi.org/10.1007/BF00374653

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  • DOI: https://doi.org/10.1007/BF00374653

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