Tohoku J. Exp. Med., 2001, 193 (4)

Cardiac Twitch Properties Simulated by Three States Model

HIDEYUKI HONDA, TAIHEI NAYA¹ and YOSHIRO KOIWA¹

The Faculty of Medical Science and Welfare, Tohoku Bunka Gakuen University, Sendai 981-8551, and
¹The First Department of Internal Medicine, Tohoku University School of Medicine, Sendai 980-8575

We examined whether the three states model can explain the systolic and relaxation properties of cardiac muscle to clarify what factors affect these properties. Changing the values of the parameters describing the calcium transient and calcium sensitivity, we estimated the effects of these parameters on the systolic and relaxation properties of twitch contraction. The simulations showed the following four features: 1) An increase in the maximum calcium concentration and calcium sensitivity, and a prolongation of the calcium transient led to an increase in peak tension associated with an increase in the time to peak tension. 2) An increase in myosin ATPase activity led to an increase in peak tension associated with a decrease in the time to peak tension. 3) An increase of peak tension was accompanied by a prolongation of the late systolic period. 4) The constant of the late tension relaxation from 25% to 10% of the peak tension was altered when the crossbridge cycling rate, the resting calcium concentration or the late decline of the calcium transient was changed. The simulation were not contradictory to the experimental results and showed that three state muscle model can provide qualitative descriptions on the systolic and relaxation characteristics of cardiac muscle.

Keywords —— twitch contraction; cardiac muscle; calcium transient; crossbridge kinetics; three states model

© 2001 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2001, 193, 259-277

Address for reprint: Hideyuki Honda, The Faculty of Medical Science and Welfare, Tohoku Bunka Gakuen University, 6-45-16 Kunimi, Aoba-ku, Sendai 981-8551, Japan.

e-mail: hideyuki@rehab.tbgu.ac.jp

We dedicate this article to late Ichiro Matsubara who was deceased in 1990. One of the authors was the last student and also the co-worker of him. The discussion with him gave the inspiration to the authors to construct the muscle model to explain the results of X-ray diffraction studies done by him and his colleagues, although the authors have all the responsibility for the article. The period we worked with him was short, but his sincere attitude and calm passion to research has been an encouragement for us.