FIGURE 4.

Respiration associated with force-frequency relations. O₂ consumption simulated by the ECME model (A) and measured in rat ventricular trabeculae (B) as a function of the pacing frequency at various extracellular Ca²⁺ levels. The plots in panel A were obtained from the same simulations reported in Fig. 3. The experimentally determined rate of respiration, V_O2, is expressed relative to the maximum observed when the muscle was exposed to the uncoupler FCCP. Treatment with 5 mM NaCN completely inhibited the respiratory flux. The simulated V_O2 was averaged after the model reached a pseudo-steady state. Under steady-state resting conditions, V_O2 averaged 0.08 mM s⁻¹.