BS-526-04 IMPAIRED REDOX RESPONSE TO INCREASED WORKLOAD IN ATRIAL MITOCHONDRIA FROM PATIENTS WITH ATRIAL FIBRILLATION

Abstract

Calcium handling abnormalities contribute to the pathophysiology of atrial fibrillation (AF). In ventricular myocytes, Ca2+ has been shown to play an important role in mitochondrial response to increased workload by activating key dehydrogenases in the Krebs cycle, necessary for NAD(P)H regeneration and, ultimately, neutralisation. We hypothesise that workload response of mitochondria is impaired in atrial cardiomyocytes from patients with AF. Membrane currents (patch clamp), cytosolic Ca2+ (Fluo-3) and NAD(P)H/FAD autofluorescence were recorded in right atrial myocytes from sinus rhythm (CTL) or AF patients. Immunofluorescence labeling together with STED microscopy and EM microscopy were employed to characterize interaction between mitochondria and sarcoplasmic reticulum (SR). Diastolic [Ca2+]i of voltage-clamped myocytes was comparable, whereas amplitudes of L-type Ca2+ current and triggered of Ca2+ transients (CaTs) were decreased by 49% and 43%, respectively. Basal level of NAD(P)H at 0.5 Hz stimulation frequency was comparable in CTL and AF (73.08±2.62%, n=14/7 vs. 81.05±5.39%, n=4/3 respectively), suggesting a similar redox index. In all CTL cells, upon increasing stimulation frequency to 3 Hz and subsequent β-adrenergic stimulation, the NAD(P)H level initially decreased but recovered to a level comparable to basal state. In contrast, 35% of AF myocytes lost this capacity to recover. Electron and STED microscopy images (Figure) show a disturbance in mitochondrial organisation and their interaction with the SR. Impaired cytosolic Ca2+ handling and disturbed interaction between mitochondrial and Ca2+ release sites of the SR may contribute to the impaired redox response of mitochondria to increased workload which we observed in AF patients. This likely results in impaired ATP production and ROS neutralisation, which may finally contribute to atrial arrhythmogenesis in AF patients.