Palmitoyl-carnitine increases RyR2 oxidation and sarcoplasmic reticulum Ca²⁺ leak in cardiomyocytes: Role of adenine nucleotide translocase

Long chain fatty acids bind to carnitine and form long chain acyl carnitine (LCAC), to enter into the mitochondria. They are oxidized in the mitochondrial matrix. LCAC accumulates rapidly under metabolic disorders, such as acute cardiac ischemia, chronic heart failure or diabetic cardiomyopathy. LCAC accumulation is associated with severe cardiac arrhythmia including ventricular tachycardia or fibrillation. We thus hypothesized that palmitoyl-carnitine (PC), alters mitochondrial function leading to Ca²⁺ dependent-arrhythmia. In isolated cardiac mitochondria from C57Bl/6 mice, application of 10μM PC decreased adenine nucleotide translocase (ANT) activity without affecting mitochondrial permeability transition pore (mPTP) opening. Mitochondrial reactive oxygen species (ROS) production, measured with MitoSOX Red dye in isolated ventricular cardiomyocytes, increased significantly under PC application. Inhibition of ANT by bongkrekic acid (20μM) prevented PC-induced mitochondrial ROS production. In addition, PC increased type 2 ryanodine receptor (RyR2) oxidation, S-nitrosylation and dissociation of FKBP12.6 from RyR2, and therefore increased sarcoplasmic reticulum (SR) Ca²⁺ leak. ANT inhibition or anti-oxidant strategy (N-acetylcysteine) prevented SR Ca²⁺ leak, FKBP12.6 depletion and RyR2 oxidation/S-nitrosylation induced by PC. Finally, both bongkrekic acid and NAC significantly reduced spontaneous Ca²⁺ wave occurrences under PC. Altogether, these results suggest that an elevation of PC disturbs ANT activity and alters Ca²⁺ handling in a ROS-dependent pathway, demonstrating a new pathway whereby altered FA metabolism may contribute to the development of ventricular arrhythmia in pathophysiological conditions.