Blocking late sodium current reduces hydrogen peroxide-induced arrhythmogenic activity and contractile dysfunction

Area of Science:

• Cardiology
• Electrophysiology
• Biochemistry

Background:

• Reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), are implicated in intracellular calcium overload and ischemia-reperfusion injury.
• Existing research suggests a link between ROS and cardiac dysfunction, but the underlying ionic mechanisms require further elucidation.

Purpose of the Study:

• To investigate the hypothesis that H2O2-induced cardiac arrhythmias and contractile dysfunction result from an increase in the late sodium current (late INa).
• To evaluate the therapeutic potential of late INa inhibition in mitigating H2O2-induced cellular damage.

Main Methods:

• Ventricular myocytes isolated from guinea pigs and rabbits were exposed to H2O2 (200 microM).
• Whole-cell patch-clamp technique and video edge detection were used to measure transmembrane potentials, currents, and cell contraction.
• Intracellular sodium ([Na+]i) and calcium ([Ca2+]i) levels were determined using fluorescence measurements.
• The effects of tetrodotoxin (TTX) and ranolazine, a late INa inhibitor, were assessed.

Main Results:

• H2O2 induced a persistent late INa, prolonged action potential duration (APD), and caused early afterdepolarizations (EADs) and aftercontractions.
• H2O2 exposure led to increased intracellular sodium and calcium levels.
• Ranolazine significantly attenuated H2O2-induced late INa, APD prolongation, and EADs, while also accelerating relaxation and preventing aftercontractions.
• Pretreatment with ranolazine reduced H2O2-induced increases in APD, [Na+]i, and [Ca2+]i.

Conclusions:

• The study confirms that increased late INa contributes significantly to H2O2-induced electrical and contractile dysfunction in ventricular myocytes.
• Inhibition of the late sodium current presents a promising therapeutic strategy to protect against sodium and calcium overload caused by ROS.