Methylene blue counteracts H₂S toxicity-induced cardiac depression by restoring l-type ca channel activity

We have previously reported that methylene blue (MB) can counteract hydrogen sulfide (H₂S) intoxication-induced circulatory failure. Because of the multifarious effects of high concentrations of H₂S on cardiac function, as well as the numerous properties of MB, the nature of this interaction, if any, remains uncertain. The aim of this study was to clarify 1) the effects of MB on H₂S-induced cardiac toxicity and 2) whether L-type Ca²⁺ channels, one of the targets of H₂S, could transduce some of the counteracting effects of MB. In sedated rats, H₂S infused at a rate that would be lethal within 5 min (24 μM·kg⁻¹·min⁻¹), produced a rapid fall in left ventricle ejection fraction, determined by echocardiography, leading to a pulseless electrical activity. Blood concentrations of gaseous H₂S reached 7.09 ± 3.53 μM when cardiac contractility started to decrease. Two to three injections of MB (4 mg/kg) transiently restored cardiac contractility, blood pressure, and V̇o₂, allowing the animals to stay alive until the end of H₂S infusion. MB also delayed PEA by several minutes following H₂S-induced coma and shock in unsedated rats. Applying a solution containing lethal levels of H₂S (100 μM) on isolated mouse cardiomyocytes significantly reduced cell contractility, intracellular calcium concentration ([Ca²⁺]_i) transient amplitudes, and L-type Ca²⁺ currents (I_Ca) within 3 min of exposure. MB (20 mg/l) restored the cardiomyocyte function, ([Ca²⁺]_i) transient, and I_Ca. The present results offer a new approach for counteracting H₂S toxicity and potentially other conditions associated with acute inhibition of L-type Ca²⁺ channels.