Figure 1.
General scheme of guinea pig cardiomyocyte model.
The electrophysiological module describes major ion channels underlying the action potential, E-C coupling and Ca2+ handling. The mitochondrial module accounts for major components of mitochondrial energetics such as TCA cycle. The ROS-induced ROS release (RIRR) module describes ROS production, transport and scavenging. The mitochondrial energetics and RIRR are linked to Ca2+ handling and cellular electrophysiology through signaling ions (e.g., Ca2+ and Na+) and metabolic intermediates (e.g. ATP). In the figure, shunt represents the fraction of ROS production from the electron transport chain, and p1 and p2 represent the fraction of Ca2+ that MCU take up from the cytosol and the mitochondria-SR microdomain, respectively.
Figure 2.
Model simulated effects of MCU Ca2+ uptake pool on [Ca2+]i and [Ca2+]m under control (A and C) and NKA inhibition (B and D) conditions during the transition of increasing pacing (from 0.25 Hz to 2 Hz).
Different colors represent different p1:p2 ratios: red (1∶0); green (3∶1); black (1∶1); blue (1∶3); and pink (0∶1). (E). Summarized effect of p1:p2 ratio on [Ca2+]m accumulation in response to increased energy demand. (F) Experimental data of the effect of NKA inhibition on [Ca2+]m accumulation (Reproduced from [1] with permission). The pacing frequency was increased to 1 Hz at 60 s.
Figure 3.
Effects of blocking NKA on ion homeostasis and mitochondrial energetics under low O2− production conditions with or without concurrent mNCE inhibition.
The cell was paced at 0.25: control; Red: 50% NKA inhibition; Dark green: 50% NKA inhibition+60% mNCE inhibition. (A): [Na+]i; (B): [Na+]m; (C): [Ca2+]i; (D): [Ca2+]m; (E): NADH; (F): ROS; and (G): mitochondrial membrane potential (ΔΨm). In this simulation, shunt = 1% and p1:p2 = 1∶3. Inserts: Experimental data of effects of ouabain (red) and CGP-37157 (dark green) on diastolic [Ca2+]m (Insert D), NADH (Insert E), and oxidative stress (Insert F) (Reproduced from [1]). In insert F, ouabain and CGP-37157 were applied at 1 min and pacing frequency was increased to 1 Hz at 5 min.
Figure 4.
Effects of blocking NKA on ion homeostasis and mitochondrial energetics under higher O2− production conditions with or without concurrent mNCE inhibition.
Black: control; Red: 50% NKA inhibition; Blue grey: 50% NKA inhibition+60% mNCE inhibition; Dark green: 50% NKA inhibition+90% mNCE inhibition. (A): [Na+]i; (B): [Na+]m; (C): [Ca2+]i; (D): [Ca2+]m; (E): NADH; (F): ROS; and (G): mitochondrial membrane potential (ΔΨm). In this simulation, shunt = 2.5% and p1:p2 = 1∶3.
Figure 5.
Effect of enhancing MCU on NKA inhibition-induced mitochondrial energetic dysfunction.
Black: control; Red: 50% NKA inhibition; Dark green: 50% NKA inhibition+100% MCU enhancement. (A): [Na+]i; (B): [Na+]m; (C): [Ca2+]i; (D): [Ca2+]m; (E): NADH; (F): ROS; and (G): mitochondrial membrane potential (ΔΨm). In this simulation, shunt = 1% and p1:p2 = 1∶3.
Figure 6.
Action potential (AP) and Ca2+ alternans induced by NKA inhibition.
The cell was paced at 0.25(by 50%). AP and Ca2+ alternans were observed at the end of pacing. Black: control; Red: 50% NKA inhibition; Dark green: 50% NKA inhibition+90% mNCE inhibition. (A): mitochondrial membrane potential (ΔΨm); (B): ATPi; (C): SERCA Ca2+ uptake; (D): [Ca2+]SR; (E): [Ca2+]i and (F): AP. In this simulation, shunt = 2.5% and p1:p2 = 1∶3.
Figure 7.
Comparisons of ATPi (A and B), [Ca2+]SR (C and D), [Ca2+]i (E and F), and action potential (AP) (G and H) before (Black), during (Red) and after (Dark green) the 5th (A,C,E,G) and 9th (B,D,F,H) mitochondrial depolarization (marked with arrows in Fig. 6A).
In this simulation, shunt = 2.5%, p1:p2 = 1∶3, and NKA inhibition was 50%.
Figure 8.
Summary of [Ca2+]i and mitochondrial energetics under 0.25 Hz, 2 Hz, 2 Hz + NKA inhibition, and 2 Hz + NKA inhibition + mNCE inhibition conditions.
(A): [Ca2+]i, NADH and ROSm; and (B): ADPm, complex V activity (VATPase) and respiration rate (VO2). The data was recorded at the end point of simulations (i.e. 3 mins after increasing pacing). In this simulation shunt = 1%, p1:p2 = 1∶3, and NKA inhibition was 50%.