FIGURE 7.

Effect of changing the myofibrillar ATPase and mitochondrial Ca²⁺ uniporter on the ECME model energetic behavior after changes in workload. (A) The behavior of NADH in simulations with the pacing protocol and parametric conditions as described in the legend of Fig. 5, except that the maximal rate of ATP hydrolysis by the AM-ATPase was decreased to one-half (solid trace; mM ms⁻¹) of the control value (shaded trace). (B) The profile of average ATP_i for changes in workload under control conditions (shaded trace) or with decreased myofibrillar ATPase activity (solid trace). (C) The NADH profile in model simulations with the same pacing protocol and parameters as described in the legend of Fig. 5, but with the maximal rate of the mitochondrial Ca²⁺ uniporter decreased to 1/10th (solid trace; mM ms⁻¹) of the control value (shaded trace). (D) The profile of [Ca²⁺]_m accumulation for the low uniporter condition described in panel C (solid trace) as compared to the control (shaded trace).