We carried out a simulation study to obtain insight into the relation between calcium (Ca
2+) transients and energy for handling Ca
2+ in excitation-contraction (EC) coupling. The simulation incorporated basic Ca
2+ kinetics among total released Ca
2+ from sarcoplasmic reticulum (SR), myoplasmic free Ca
2+ ion concentration, and troponin (Tn)-Ca complex concentration ([TnCa]). The total Ca
2+ released from the SR was arbitrarily set as an impulse and three rate constants were used for Ca
2+ binding to Tn, Ca
2+ dissociation from Tn, and Ca
2+ uptake by SR. The results showed that the peak Ca
2+ transient varies widely as a reciprocal of the Ca
2+ sensitivity of the contractile machinery, despite constant total released Ca
2+ and hence, a constant energy for Ca
2+ handling. This result suggests a disproportate relationship between the magnitude of Ca2+ transients and the energy for Ca
2+ handling when the Ca
2+ sensitivity of contractile machinery changes.
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