Late Sodium Current Inhibitors as Potential Antiarrhythmic Agents

Based on recent findings, an increased late sodium current (INa,late) plays an important pathophysiological role in cardiac diseases, including rhythm disorders. The article first describes what is INa,late and how it functions under physiological circumstances. Next, it shows the wide range of cellular mechanisms that can contribute to an increased INa,late in heart diseases, and also discusses how the upregulated INa,late can play a role in the generation of cardiac arrhythmias. The last part of the article is about INa,late inhibiting drugs as potential antiarrhythmic agents, based on experimental and preclinical data as well as in the light of clinical trials

Calcium Handling Defects and Cardiac Arrhythmia Syndromes

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9-anthracene carboxylic acid is more suitable than DIDS for characterization of calcium-activated chloride current during canine ventricular action potential

Abstract Background Understanding the role of ionic currents in shaping the cardiac action potential (AP) has great importance as channel malfunctions can lead to sudden cardiac death by inducing arrhythmias. Therefore, researchers frequently use inhibitors to selectively block a certain ion channel like 4,4’-diisothiocyanostilbene-2,2’-disulfonic acid (DIDS) and 9-anthracene carboxylic acid (9-AC) for calcium-activated chloride current (ICl(Ca)). This study aims to explore which blocker is preferable to study ICl(Ca). Methods Whole-cell voltage-clamp technique was used to record ICa,L, IKs, IKr and IK1, while action potentials were measured using sharp microelectrodes. Results DIDS- (0.2 mM) and 9-AC- (0.5 mM) sensitive currents were identical in voltage-clamp conditions, regardless of intracellular Ca2+ buffering. DIDS-sensitive current amplitude was larger with the increase of stimulation rate and correlated well with the rate-induced increase of calcium transients. Both drugs increased action potential duration (APD) to the same extent but the elevation of the plateau potential was more pronounced with 9-AC at fast stimulation rates. On the contrary, 9-AC did not influence either the AP amplitude or the maximal rate of depolarization (Vmax) but DIDS caused marked reduction of Vmax. Both inhibitors reduced the magnitude of phase-1 but at slow stimulation rates this effect of DIDS was larger. All of these actions on APs were reversible upon washout of the drugs. Increasing concentrations of 9-AC between 0.1- 0.5 mM in a cumulative manner gradually reduced phase-1 and increased APD. 1 mM 9-AC had no additional actions upon perfusion after 0.5 mM. The half-effective concentration of 9-AC was approximately 160 μM with a Hill coefficient of 2. The amplitudes of ICa,L, IKs, IKr and IK1 were not changed by 0.5 mM 9-AC. Conclusions These results suggest that DIDS is equally useful to study ICl(Ca) during voltage-clamp but 9-AC is superior in AP measurements for studying the physiological role of ICl(Ca) due to the lack of sodium channel inhibition. 9-AC has also no action on other ion currents (ICa,L, IKr, IKs, IK1), however, ICa,L tracings can be contaminated with ICl(Ca) when measured in voltage-clamp condition