Positive inotropism in hypothermia partially depends on an increase in maximal Ca2+-activated force

H. Kusuoka, Y. Ikoma, S. Futaki, H. Suga, A. Kitabatake, T. Kamada, M. Inoue

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37 Scopus citations


We investigated the contribution of maximal Ca2+-activated force to the positive inotropism induced by mild hypothermia. Phosphorus-31 nuclear magnetic resonance spectroscopy revealed that neither energy-related phosphorus compounds in myocardium nor intracellular pH was responsible for the change in contractility. Maximal Ca2+-activated pressure (MCAP), the intact-heart correlate of maximal Ca2+-activated force, was determined in isolated perfused rabbit hearts by measuring isovolumic left ventricular pressure during tetani at extracellular Ca2+ concentrations ≥ 10 mM. Tetani were elicited by rapid pacing after exposure to ryanodine. MCAP increased by 2.17 ± 0.28% (means ± SE, P < 0.001, n = 19) for each degree of myocardial cooling between 30 and 38°C. Our results indicate that a primary change in myofilament Ca2+ responsiveness underlies the positive inotropism in hypothermia. The increase in maximal Ca2+-activated force may explain the observation of positive inotropism without an upward shift in the relation between oxygen consumption and pressure-volume area, as previously reported for cooled whole hearts.

Original languageEnglish (US)
Pages (from-to)H1005-H1010
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number4 30-4
StatePublished - 1991


  • excitation-contraction coupling
  • myofilament Ca responsiveness
  • phosphorus-31 nuclear magnetic resonance

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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