Mitochondrial Bioenergetics During Ischemia and Reperfusion

Area of Science:

• Cardiovascular Physiology
• Mitochondrial Biology
• Cellular Energetics

Background:

• Ischemia-reperfusion (I/R) impairs mitochondrial energy supply and alters cardiomyocyte calcium homeostasis.
• Mitochondrial calcium ([Ca2+]m) is regulated by the uniporter (UCam) and Na+/Ca2+ exchanger (mNCX), influenced by mitochondrial membrane potential (ΔΨm).
• Cardiac energetic assessment traditionally uses oxygen consumption, but total heat release offers a comprehensive measure of energy expenditure.

Purpose of the Study:

• To investigate the role of mitochondrial calcium transporters in the energetic dysfunction of stunned rat hearts following no-flow ischemia-reperfusion (I/R).
• To explore the influence of thyroid status and cardioprotective agents on mitochondrial function and cardiac stunning.
• To elucidate the interplay between mitochondria and sarcoplasmic reticulum (SR) in regulating calcium handling and energy consumption during I/R.

Main Methods:

• Isolated rat hearts were perfused in a flow-calorimeter measuring left ventricular pressure (LVP) and total heat rate (Ht) at 30°C or 37°C.
• Hearts underwent pharmacological treatment before no-flow I/R; post-ischemic contractile (PICR) and energetic (Ht) recovery, and muscle economy (Eco) were assessed.
• Mitochondrial-sarcoplasmic reticulum (SR) interactions were evaluated using selective inhibitors and caffeine-induced contracture (CIC) during reperfusion.

Main Results:

• Mitochondrial calcium transport significantly influences post-ischemic contractile recovery and energy consumption during stunning.
• Inhibition of mNCX or pyruvate addition accelerated relaxation and increased energy consumption (EC) during caffeine-induced contracture (CIC).
• Thyroid alterations (hyperthyroidism/hypothyroidism) affected CIC and EC, indicating mitochondria's role in regulating SR calcium stores and release.

Conclusions:

• Mitochondria actively regulate cytosolic and SR calcium levels, impacting cardiac stunning and energy expenditure post-I/R.
• Mitochondrial calcium transporters are crucial targets for understanding and potentially mitigating I/R-induced cardiac dysfunction.
• The study highlights the integrated role of mitochondrial calcium handling in cardiac energetics and contractile function under stress.