Cardiac twitch properties simulated by three states model

We examined whether the three states model can explain the systolic and rel axation properties of cardiac muscle to clarify what factors affect these p roperties. Changing the values of the parameters describing the calcium tra nsient and calcium sensitivity, we estimated the effects of these parameter s on the systolic and relaxation properties of twitch contraction. The simu lations showed the following four features: 1) An increase in the maximum c alcium concentration and calcium sensitivity, and a prolongation of the cal cium transient led to an increase in peak tension associated with an increa se in the time to peak tension. 2) An increase in myosin ATPase activity le d 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 prolongat ion of the late systolic period. 4) The constant of the late tension relaxa tion from 25% to 10% of the peak tension was altered when the crossbridge c ycling rate, the resting calcium concentration or the late decline of the c alcium transient was changed. The simulation were not contradictory to the experimental results and showed that three state muscle model can provide q ualitative descriptions on the systolic and relaxation characteristics of c ardiac muscle. (C) 2001 Tohoku University Medical Press.