Methylene blue counteracts cyanide cardiotoxicity: cellular mechanisms

In adult left ventricular mouse myocytes, exposure to sodium cyanide (NaCN) in the presence of glucose dose-dependently reduced contraction amplitude, with similar to 80% of maximal inhibitory effect attained at 100 mu M. NaCN (100 mu M) exposure for 10 min significantly decreased contraction and intracellular Ca2+ concentration ([Ca2+](i)) transient amplitudes, systolic but not diastolic [Ca2+](i), and maximal L-type Ca2+ current (I-Ca) amplitude, indicating acute alteration of [Ca2+](i) homeostasis largely accounted for the observed excitation-contraction abnormalities. In addition, NaCN depolarized resting membrane potential (E-m), reduced action potential (AP) amplitude. prolonged AP duration at 50% (APD(50)) and 90% repolarization (APD(90)), and suppressed depolarization-activated K+ currents but had no effect on Na+-Ca2+ exchange current (I-Naca). NaCN did not affect cellular adenosine triphosphate levels but depolarized mitochondrial membrane potential (Delta psi(m)) and increased superoxide O-2(-) levels. Methylene blue (MB; 20 mu g/ml) added 3 min after NaCN restored contraction and [Ca2+](i) transient amplitudes, systolic [Ca2+](i), E-m, AP amplitude, APD(50), APD(90), I-Ca, depolarization activated K+ currents, Delta psi(m) and O-2(-) levels toward normal. We conclude that MB reversed NaCN-induced cardiotoxicity by preserving intracellular Ca2+ homeostasis and excitation-contraction coupling (I-Ca), minimizing risks of arrhythmias (E-m, AP configuration, and depolarization-activated K+ currents), and reducing O-2(-) levels. NEW & NOTEWORTHY Cyanide poisoning due to industrial exposure, smoke inhalation, and bioterrorism manifests as cardiogenic shock and requires rapidly effective antidote. In the early stage of cyanide exposure, adenosine triphosphate levels are normal but myocyte contractility is reduced, largely due to alterations in Ca2+ homeostasis because of changes in oxidation-reduction environment of ion channels. Methylene blue, a drug approved by the U.S. Food and Drug Administration, ameliorates cyanide toxicity by normalizing oxidation-reduction state and Ca2+ channel function.