Altered spatiotemporal dynamics of the mitochondrial membrane potential in the hypertrophied heart

Abstract

Chronically elevated levels of oxidative stress resulting from increased production and/or impaired scavenging of reactive oxygen species are a hallmark of mitochondrial dysfunction in left ventricular hypertrophy. Recently, oscillations of the mitochondrial membrane potential (DeltaPsi(m)) were mechanistically linked to changes in cellular excitability under conditions of acute oxidative stress produced by laser-induced photooxidation of cardiac myocytes in vitro. Here, we investigate the spatiotemporal dynamics of DeltaPsi(m) within the intact heart during ischemia-reperfusion injury. We hypothesize that altered metabolic properties in left ventricular hypertrophy modulate DeltaPsi(m) spatiotemporal properties and arrhythmia propensity.

Figure 1

(A) Three representative traces (A–C) from a total of 6400 pixels are shown indicating the measurement of background fluorescence used to monitor relative changes in ΔΨ_m. Also shown is the background fluorescence during and after (for up to 300 min) the dye-loading and washout procedures. These data demonstrate the stability of TMRM fluorescence during steady-state perfusion. The steady-state level of TMRM fluorescence for each pixel is used for normalization purposes. (B) Representative ECG images of a sham-operated and an aortic-banded LVH heart. H&E-stained histological sections from sham-operated and LVH hearts indicate marked concentric hypertrophy in aortic banded animals. Also shown are representative optical AP traces measured in representative di-4-ANEPPS-stained normal and LVH hearts during steady-state pacing.

Figure 2

(A) Average and SD of ΔΨ_m response to IR injury in normal and LVH hearts. Clearly, LVH prevents ischemia-induced depolarization of ΔΨ_m. (B) Average ΔΨ_m response during the entire episode of ischemia (over 7 min) and reperfusion in normal and LVH hearts. LVH is associated with a significantly more polarized ΔΨ_m during both ischemia and reperfusion.

Figure 3

Contour maps showing the spatiotemporal distribution of ΔΨ_m during the course of ischemia (top row) and reperfusion (bottom row) in representative normal (A) and LVH (B) hearts.

Figure 4

ΔΨ_m contour maps recorded after 7 min of ischemia in representative normal (A) and LVH (B) hearts. (Right) Multiple traces recorded from the same normal and LVH hearts during the course of IR injury.

Figure 5

(A) Spatial heterogeneity indexed by the SD of ΔΨ_m in normal and LVH hearts. (B) Average and SD of ΔΨ_m heterogeneity measured during ischemia and reperfusion in normal and LVH hearts.

Figure 6

AS as an index of spontaneous arrhythmias measured during ischemia and reperfusion from all unpaced normal and LVH hearts. Representative ECG traces indicate progressively more complex arrhythmias, ranging from AS 0 to 5. AS: arrhythmia score.

Figure 7

Incidence of VT/VF in paced hearts during IR injury. Representative volume-conducted ECG traces measured at baseline, during early and late ischemia, and after reperfusion in control (left) and LVH (right) hearts. VT/VF was observed exclusively in paced LVH hearts. Representative AP traces from control and LVH hearts demonstrate rapid shortening of APD in LVH but not control hearts in response to 7 min of ischemia (bottom).