Related Experiment Video
Updated: Sep 26, 2026

Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca2+ Transients and Membrane Currents
Published on: July 3, 2013
Effects of the chromanol HMR 1556 on potassium currents in atrial myocytes
Ralph F Bosch1, Alexander C Schneck, Saskia Csillag
1Abteilung III, Medizinische Klinik, Otfried-Müller-Strasse 10, 72076 Tübingen, Germany. ralph.bosch@uni-tuebingen.de
Purpose:
The chromanol HMR 1556 is a potent blocker of KvLQT1/minK potassium channels expressed in Xenopus oocytes. The compound is therefore a new class III antiarrhythmic drug with a distinct mechanism of action. However, the effect of HMR 1556 on atrial ion channels and the selectivity of block in the human heart has not been investigated. We tested the effects of HMR 1556 on repolarizing potassium currents in human and guinea pig atrial myocytes.
Methods And Results:
Single atrial myocytes were isolated by enzymatic dissociation. Atrial potassium currents (I(Ks), I(Kr), in guinea pig, I(to), I(Kur), I(K1) in humans) were recorded at 36 degrees C in the whole cell mode of the patch clamp technique. HMR 1556 produced a concentration-dependent and reversible block of I(Ks) with a half maximal concentration (EC(50)) of 6.8 nmol/l. 10 micromol/l HMR 1556 almost completely inhibited I(Ks) (97.2+/-3.2%, n=6). Steady-state activation as well as kinetic properties of the current were not altered by HMR 1556. I(Kr) currents were not affected up to concentrations of 10 micromol/l. HMR 1556 did not inhibit other potassium currents in human atrium: I(to), I(Kur) and the classical inward rectifier potassium current I(K1) were not significantly affected up to concentrations that completely blocked I(Ks) (10 micromol/l).
Conclusions:
HMR 1556 is a highly-potent blocker of I(Ks) channels without exerting effects on other potassium currents involved in atrial repolarization. Given the potential advantages of I(Ks) vs. I(Kr) blockade, the drug's new mechanism of action warrants further investigation to clarify its role as an antiarrhythmic agent.
Related Concept Videos
Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers
G-Protein Gated Ion Channels
Sensory organs,...
Electrophysiology of Normal Cardiac Rhythm
Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers
Class 1A Antiarrhythmic Drugs: These drugs work by moderately blocking sodium channels,...
Cardiac Action Potential
The cardiac action potential process involves a series of phases characterized by the movement of ions across the cardiac cell membranes, leading to the depolarization and repolarization of the cardiac myocytes.
Ionic Basis of Cardiac Action Potentials
Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

