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Amiodarone inhibits apamin-sensitive potassium currents.

Isik Turker¹, Chih-Chieh Yu, Po-Cheng Chang

¹Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.

|August 8, 2013

Summary

Amiodarone and its metabolite desethylamiodarone inhibit the apamin-sensitive potassium current (I KAS) in human SK2 channels. This inhibition, dependent on intracellular calcium, may explain amiodarone

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Area of Science:

Cardiovascular Pharmacology
Ion Channel Physiology
Cardiac Electrophysiology

Background:

The apamin-sensitive potassium current (I KAS), mediated by SK2 channels, is crucial for action potential duration shortening in failing ventricles.
SK2 channel dysfunction is implicated in recurrent ventricular fibrillation (VF) in heart failure.

Purpose of the Study:

To investigate the hypothesis that amiodarone inhibits I KAS in human embryonic kidney 293 (HEK-293) cells expressing SK2 channels.
To characterize the dose- and voltage-dependence of amiodarone's effect on I KAS.
To assess the inhibitory effects of amiodarone's metabolite, desethylamiodarone, on I KAS.

Main Methods:

Utilized the patch-clamp technique to record I KAS in HEK-293 cells stably expressing human SK2 channels.
Administered varying concentrations of amiodarone and desethylamiodarone.
Assessed current inhibition under different intracellular calcium (Ca2+) concentrations and voltage potentials.

Main Results:

Amiodarone demonstrated dose-dependent inhibition of I KAS, with an IC50 of 2.67 ± 0.25 µM.
Maximal inhibition (85.6 ± 3.1%) was achieved with 50 µM amiodarone.
Inhibition was voltage-independent but significantly dependent on intracellular Ca2+ concentration; desethylamiodarone also inhibited I KAS in a Ca2+-dependent manner.

Conclusions:

Both amiodarone and desethylamiodarone inhibit I KAS at therapeutic concentrations.
The observed SK2 channel inhibition is independent of time and voltage but relies on intracellular Ca2+ levels.
This I KAS inhibition may contribute to amiodarone's efficacy in preventing electrical storm in failing hearts.