Integration of mitochondrial energetics in heart with mathematical modelling

It has been an unsolved question how cardiac mitochondrial energetics is regulated during working transition. Mathematical modelling is a powerful tool for exploring the complicated networks of mitochondrial metabolism. We summarize the recent progress and remaining questions about mitochondrial energetics in heart, especially focusing on approaches utilizing mathematical modelling. Feedback activation by ADP and/or inorganic phosphate is an old but still attractive hypothesis for explaining the regulation mechanisms of cardiac mitochondrial energetics. However, this hypothesis has not been fully validated by experiments because rises of ADP and/or inorganic phosphate concentrations during cardiac workload increase have not been detected in many experiments. The hypothesis of intracellular energetic units is an extended version of feedback activation, which has a similar problem. The each-step activation hypothesis beautifully reproduces metabolite constancy, although such master regulators have not been identified yet. Ca²⁺ has been the most plausible candidate because some of the mitochondrial dehydrogenases are activated by it. Recent experimental and simulation studies, however, throw doubt on its physiological relevance. Finally, we discuss issues to be solved to obtain a better view of cardiac mitochondrial energetics.