Quantitative in vivo mapping of myocardial mitochondrial membrane potential
January
Quantitative in vivo mapping of myocardial mitochondrial membrane potential
Nathaniel M. Alpert 0 1
Nicolas Guehl 0 1
Leon Ptaszek 1
Matthieu Pelletier-Galarneau 0 1
Jeremy Ruskin 1
Moussa C. Mansour 1
Dustin Wooten 0 1
Chao Ma 0 1
Kazue Takahashi 0 1
Yun Zhou 1
Timothy M. Shoup 0 1
Marc D. Normandin 0 1
Georges El Fakhri 0 1
0 Gordon Center for Medical Imaging, Massachusetts General Hospital, Harvard Medical School , Boston , Massachusetts, United States of America, 2 Cardiac Arrhythmia Service, Massachusetts General Hospital, Harvard Medical School , Boston , Massachusetts, United States of America, 3 The Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine Johns Hopkins University , Baltimore, Maryland , United States of America
1 Editor: Cecilia Zazueta, Instituto Nacional de Cardiologia Ignacio Chavez , MEXICO
Mitochondrial membrane potential (ΔΨm) arises from normal function of the electron transport chain. Maintenance of ΔΨm within a narrow range is essential for mitochondrial function. Methods for in vivo measurement of ΔΨm do not exist. We use 18F-labeled tetraphenylphosphonium (18F-TPP+) to measure and map the total membrane potential, ΔΨT, as the sum of ΔΨm and cellular (ΔΨc) electrical potentials.
-
Funding: This work was funded by two grants from
the United States National Institutes of Health:
R01HL110241 (GEF) and R01HL137230 (GEF),
https://www.nhlbi.nih.gov. These grants were
awarded as part of the standard peer review
process for new grants. The study design and
analysis are solely the work of the study authors,
meaning that the funders had no role in study
Background
Methods
(mV).
Results
Eight pigs, five controls and three with a scar-like injury, were studied. Pigs were studied
with a dynamic PET scanning protocol to measure 18F-TPP+ volume of distribution, VT.
Fractional extracellular space (fECS) was measured in 3 pigs. We derived equations
expressing ΔΨT as a function of VT and the volume-fractions of mitochondria and fECS.
Seventeen segment polar maps and parametric images of ΔΨT were calculated in millivolts
In controls, mean segmental ΔΨT = -129.4±1.4 mV (SEM). In pigs with segmental tissue
injury, ΔΨT was clearly separated from control segments but variable, in the range -100 to
0 mV. The quality of ΔΨT maps was excellent, with low noise and good resolution.
Measurements of ΔΨT in the left ventricle of pigs agree with previous in in-vitro measurements.
Conclusions
We have analyzed the factors affecting the uptake of voltage sensing tracers and developed
a minimally invasive method for mapping ΔΨT in left ventricular myocardium of pigs. ΔΨT is
computed in absolute units, allowing for visual and statistical comparison of individual values
design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Competing interests: The authors have declared
that no competing interests exist.
with normative data. These studies demonstrate the first in vivo application of quantitative
mapping of total tissue membrane potential, ΔΨT.
Introduction
Mitochondria produce approximately 90% of cellular adenosine triphosphate (ATP) through
oxidative phosphorylation [
1
]. The electron transport chain (ETC) of the mitochondrion is
ultimately responsible for converting the foods we eat into electrical and chemical energy
gradients by pumping protons across the inner membrane in the mitochondrial intermembrane
space. The energy stored in the electric field, referred to as mitochondrial membrane potential
(ΔCm), is then used to power the conversion of ADP to ATP. In a typical cell, the ΔCm
remains constant with time and is about -140 mV [
2
]. Table 1 lists ΔCm for mitochondria of
different cell types.
If ΔCm remains within the physiological range, a small amount of reactive oxygen species
(ROS) is produced. However, in mitochondrial dysfunction, ΔCm falls outside the normal
range, with concomitant increase in ROS release, and impairment of ATP production [
10
].
And because mitochondria are the most important source of energy and ROS in the cell,
mitochondrial dysfunction is at the core of many diseases, including myopathies [
11
], diabetes
[
12
], degenerative diseases [
13
], inflammation [
14
], cancer [
15
], and cardiac arrhythmias [
16,
17
].
Despite continuing scientific interest in voltage sensitive probes, a noninvasive method for
measuring ΔCm in living animals does not currently exist. The basic physiological studies
conducted several decades ago are highly relevant but not always mentioned: Historically,
fluorescent dyes [
18
] and lipophilic cationic tracers have been developed for quantitative assay of
ΔCm in isolated mitochondria [
4
], cells [
19
], and isolated heart preparations [
6
]. Electrodes
sensitive to tetraphenylphosphonium (TPP) have also been developed and used to evaluate
ΔCm in isolated mitochondrial fractions [
9, 20
]. [14C or 3H]-labeled lipophilic catio (...truncated)