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Ceramide modulates electrophysiological characteristics and oxidative stress of pulmonary vein cardiomyocytes

Background: Ceramide is involved in regulating metabolism and energy expenditure, and its abnormal myocardial accumulation may contribute to heart injury or lipotoxic cardiomyopathy. Whether ceramide can modulate the electrophysiology of pulmonary veins (PVs) remains unknown.

Material and methods: We used conventional microelectrodes to measure the electrical activity of isolated rabbit PV tissue preparations before and after treatment with various concentrations of ceramide with or without H2 O2 (2 mM), MitoQ, wortmannin, or 740 YP. A whole-cell patch clamp and fluorescence imaging were used to record the ionic currents, calcium (Ca2+ ) transients, and intracellular reactive oxygen species (ROS) and sodium (Na+ ) in isolated single PV cardiomyocytes before and after ceramide (1μM) treatment.

Results: Ceramide (0.1, 0.3, 1, and 3 μM) reduced the beating rate of PV tissues. Furthermore, ceramide (1μM) suppressed the 2mM H2 O2 -induced faster PV beating rate, triggered activities, and burst firings, which were further reduced by MitoQ. In the presence of wortmannin, ceramide did not change the PV beating rate. The H2 O2 -induced faster PV beating rate could be counteracted by MitoQ or wortmannin with no additive effect from the ceramide. Ceramide inhibited pPI3K. Ceramide reduced Ca2+ transients, sarcoplasmic reticulum Ca2+ contents, L-type Ca2+ currents, Na+ currents, late Na+ currents, Na+ -hydrogen exchange currents, and intracellular ROS and Na+ in PV cardiomyocytes, but did not change Na+ -Ca2+ exchange currents.

Conclusion: C2 ceramide may exert the distinctive electrophysiological effect of modulating PV activities, which may be affected by PI3K pathway-mediated oxidative stress, and might play a role in the pathogenesis of PV arrhythmogenesis.

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S2758 Wortmannin Wortmannin is the first described PI3K inhibitor with IC50 of 3 nM in a cell-free assay, with little selectivity within the PI3K family. Wortmannin blocks autophagosome formation and potently inhibits DNA-PK/ATM with IC50 of 16 nM and 150 nM in cell-free assays. Wortmannin also inhibits PLK1 activity.

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