Role of Mitochondrial ROS for Calcium Alternans in Atrial Myocytes.

Area of Science:

• Cardiology
• Mitochondrial Biology
• Electrophysiology

Background:

• Atrial calcium transient (CaT) alternans, beat-to-beat alternations in CaT amplitude, are linked to atrial fibrillation (AF).
• Mitochondria regulate cardiac calcium signaling and redox balance, influencing excitation-contraction coupling.

Purpose of the Study:

• To investigate the role of mitochondrial reactive oxygen species (ROS) and antioxidant defense in atrial CaT alternans.
• To determine if modulating mitochondrial redox state can impact pro-arrhythmic CaT alternans.

Main Methods:

• Studied isolated rabbit atrial myocytes using fluorescence microscopy to measure ROS production during CaT alternans.
• Administered exogenous ROS, ROS scavengers, and specific inhibitors targeting mitochondrial ROS production and antioxidant pathways.
• Assessed the effects of these interventions on CaT alternans amplitude and pacing thresholds.

Main Results:

• Enhanced ROS production was observed during CaT alternans.
• Mitochondrial ROS (ROS_m) modulation significantly affected CaT alternans: MitoTempo diminished alternans, while inhibitors of cyt c peroxidase and electron transport chain complexes decreased severity.
• Impairment of mitochondrial antioxidant defense (e.g., inhibiting nicotinamide nucleotide transhydrogenase) exacerbated CaT alternans.

Conclusions:

• Intact mitochondrial antioxidant defense is crucial for preventing pro-arrhythmic CaT alternans.
• Targeting the mitochondrial redox state presents a potential therapeutic avenue for alternans-associated arrhythmias like AF.