Permeabilized myocardial fibers as model to detect mitochondrial dysfunction during sepsis and melatonin effects without disruption of mitochondrial network

• Permeabilized fibers of mouse myocardial yield accurate mitochondrial bioenergetic information.
• Key defects in OXPHOS and ETS capacities were identified in septic mice myocardial.
• ETC supercomplex assembly may underlie mitochondrial respiration impairment.
• Melatonin maintained mitochondrial function and supercomplex assembly during sepsis.

Analysis of mitochondrial function is crucial to understand their involvement in a given disease. High-resolution respirometry of permeabilized myocardial fibers in septic mice allows the evaluation of the bioenergetic system, maintaining mitochondrial ultrastructure and intracellular interactions, which are critical for an adequate functionality. OXPHOS and electron transport system (ETS) capacities were assessed using different substrate combinations. Our findings show a severe septic-dependent impairment in OXPHOS and ETS capacities with mitochondrial uncoupling at early and late phases of sepsis. Moreover, sepsis triggers complex III (CIII)-linked alterations in supercomplexes structure, and loss of mitochondrial density. In these conditions, melatonin administration to septic mice prevented sepsis-dependent mitochondrial injury in mitochondrial respiration. Likewise, melatonin improved cytochrome b content and ameliorated the assembly of CIII in supercomplexes. These results support the use of permeabilized fibers to identify properly the respiratory deficits and specific melatonin effects in sepsis.