Mitochondrial content and intrinsic coupling‐related differences shape bioenergetic output and redox responses across striated muscles in rats
- 1Auckland Bioengineering Institute The University of Auckland Auckland New Zealand
- 2School of Biological Sciences Faculty of Science The University of Auckland Auckland New Zealand
Abstract
Striated muscles differ markedly in energetic demand, but whether mitochondrial respiration and reactive oxygen species emission differ intrinsically across muscle types remains unclear. This study compared mitochondrial respiration, hydrogen peroxide (H2O2) emission and antioxidant enzyme expression in heart, diaphragm and hindlimb skeletal muscle from healthy rats. Mitochondrial O2 flux and H2O2 emission were measured simultaneously using high‐resolution respirometry coupled with fluorometry in tissue homogenates subjected to substrate‐uncoupler‐inhibitor titration protocols. Mitochondrial content was estimated by citrate synthase activity, and antioxidant enzyme expression was measured by immunoblotting. Heart tissue displayed the highest mitochondrial respiration and H2O2 emission when expressed per tissue mass, followed by diaphragm and skeletal muscle. However, normalisation by citrate synthase activity eliminated differences in respiratory flux between muscles, indicating that variations in tissue‐level respiration were primarily driven by mitochondrial content. Net H2O2 emission was greatest during leak respiration and decreased during oxidative phosphorylation and uncoupled states in all muscle types. Cardiac mitochondria exhibited a higher H2O2/O2 ratio during leak respiration and higher coupling‐related ratios than those of diaphragm and skeletal muscle. In association, cardiac muscle showed greater expression of the mitochondrial antioxidant enzymes superoxide dismutase 2 and catalase in a separate cohort. These findings indicate that absolute oxidative metabolism across striated muscles is largely determined by mitochondrial content, whereas respiratory capacity per mitochondrial unit was conserved. Cardiac muscle exhibits elevated leak‐associated reactive oxygen species emission but compensates by enhancing antioxidant defences, highlighting coordination between bioenergetic demand and redox regulation in continuously active muscles.
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BibTeX
@article{chan2026mitochondrial,
title = {{Mitochondrial content and intrinsic coupling‐related differences shape bioenergetic output and redox responses across striated muscles in rats}},
author = {Alex Chan and Jules Devaux and Claudia Wen and Anthony Phillips and Anthony Hickey and Toan Pham},
journal = {Experimental Physiology},
year = {2026},
month = nov,
doi = {10.1113/ep094334},
url = {https://doi.org/10.1113/ep094334},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Mitochondrial content and intrinsic coupling‐related differences shape bioenergetic output and redox responses across striated muscles in rats
AU - Alex Chan
AU - Jules Devaux
AU - Claudia Wen
AU - Anthony Phillips
AU - Anthony Hickey
AU - Toan Pham
PY - 2026
DA - 2026/11/03
JO - Experimental Physiology
DO - 10.1113/ep094334
UR - https://doi.org/10.1113/ep094334
AB - Striated muscles differ markedly in energetic demand, but whether mitochondrial respiration and reactive oxygen species emission differ intrinsically across muscle types remains unclear. This study compared mitochondrial respiration, hydrogen peroxide (H2O2) emission and antioxidant enzyme expression in heart, diaphragm and hindlimb skeletal muscle from healthy rats. Mitochondrial O2 flux and H2O2 emission were measured simultaneously using high‐resolution respirometry coupled with fluorometry in tissue homogenates subjected to substrate‐uncoupler‐inhibitor titration protocols. Mitochondrial content was estimated by citrate synthase activity, and antioxidant enzyme expression was measured by immunoblotting. Heart tissue displayed the highest mitochondrial respiration and H2O2 emission when expressed per tissue mass, followed by diaphragm and skeletal muscle. However, normalisation by citrate synthase activity eliminated differences in respiratory flux between muscles, indicating that variations in tissue‐level respiration were primarily driven by mitochondrial content. Net H2O2 emission was greatest during leak respiration and decreased during oxidative phosphorylation and uncoupled states in all muscle types. Cardiac mitochondria exhibited a higher H2O2/O2 ratio during leak respiration and higher coupling‐related ratios than those of diaphragm and skeletal muscle. In association, cardiac muscle showed greater expression of the mitochondrial antioxidant enzymes superoxide dismutase 2 and catalase in a separate cohort. These findings indicate that absolute oxidative metabolism across striated muscles is largely determined by mitochondrial content, whereas respiratory capacity per mitochondrial unit was conserved. Cardiac muscle exhibits elevated leak‐associated reactive oxygen species emission but compensates by enhancing antioxidant defences, highlighting coordination between bioenergetic demand and redox regulation in continuously active muscles.
SN - 0958-0670
SN - 1469-445X
ER -