This simulation study demonstrates a disproportionate relationship between the magnitude of calcium transients and the energy for calcium handling when the calcium sensitivity of the contractile machinery changes.
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Altered myofilament Ca sensitivity may disproportionately reduce transient amplitude; simulation extends models but leaves in vivo validation open.
We carried out a simulation study to obtain insight into the relation between calcium (Ca2+) transients and energy for handling Ca2+ in excitation-contraction (EC) coupling. The simulation incorporated basic Ca2+ kinetics among total released Ca2+ from sarcoplasmic reticulum (SR), myoplasmic free Ca2+ ion concentration, and troponin (Tn)-Ca complex concentration ([TnCa]). The total Ca2+ released from the SR was arbitrarily set as an impulse and three rate constants were used for Ca2+ binding to Tn, Ca2+ dissociation from Tn, and Ca2+ uptake by SR. The results showed that the peak Ca2+ transient varies widely as a reciprocal of the Ca2+ sensitivity of the contractile machinery, despite constant total released Ca2+ and hence, a constant energy for Ca2+ handling. This result suggests a disproportate relationship between the magnitude of Ca2+ transients and the energy for Ca2+ handling when the Ca2+ sensitivity of contractile machinery changes.
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Suga et al. (1991) studied this question.
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