System analysis of the effect of various drugs on cardiac contraction energetics

We used MoCA (Modular Control and Regulation Analysis) to demonstrate in intact beating rat heart that physiological activation of contraction by adrenaline involves the almost perfect parallel activation of both mitochondria and myofibrils by intracellular Ca²⁺. This explains the perfect homoeostasis of the energetic intermediate PCr (phosphocreatine) in heart. When using drugs specifically stimulating either supply or demand activities, MoCA helped reveal the very specific mode of regulation of heart contraction energetics. Only activation of myofibrils activity (demand), either by increasing intracellular Ca²⁺ concentration or myofibrils sensitivity to Ca²⁺, triggers activation of contractile activity. In contrast, the activation of mitochondrial activity (supply) has strictly no effect on contraction, either directly or through PCr changes (intermediate).