Methylene Blue Counteracts H 2 S-Induced Cardiac Ion Channel Dysfunction and ATP Reduction.

We have previously demonstrated that methylene blue (MB) counteracts the effects of hydrogen sulfide (H2 S) cardiotoxicity by improving cardiomyocyte contractility and intracellular Ca2+ homeostasis disrupted by H2 S poisoning. In vivo, MB restores cardiac contractility severely depressed by sulfide and protects against arrhythmias, ranging from bundle branch block to ventricular tachycardia or fibrillation. To dissect the cellular mechanisms by which MB reduces arrhythmogenesis and improves bioenergetics in myocytes intoxicated with H2 S, we evaluated the effects of H2 S on resting membrane potential (Em ), action potential (AP), Na+ /Ca2+ exchange current (INaCa ), depolarization-activated K+ currents and ATP levels in adult mouse cardiac myocytes and determined whether MB could counteract the toxic effects of H2 S on myocyte electrophysiology and ATP. Exposure to toxic concentrations of H2 S (100 µM) significantly depolarized Em , reduced AP amplitude, prolonged AP duration at 90% repolarization (APD90 ), suppressed INaCa and depolarization-activated K+ currents, and reduced ATP levels in adult mouse cardiac myocytes. Treating cardiomyocytes with MB (20 µg/ml) 3 min after H2 S exposure restored Em , APD90 , INaCa , depolarization-activated K+ currents, and ATP levels toward normal. MB improved mitochondrial membrane potential (∆ψm ) and oxygen consumption rate in myocytes in which Complex I was blocked by rotenone. We conclude that MB ameliorated H2 S-induced cardiomyocyte toxicity at multiple levels: (1) reversing excitation-contraction coupling defects (Ca2+ homeostasis and L-type Ca2+ channels); (2) reducing risks of arrhythmias (Em , APD, INaCa and depolarization-activated K+ currents); and (3) improving cellular bioenergetics (ATP, ∆ψm ).