Inhibition of IKs channels by HMR 1556

Area of Science:

• Cardiovascular Pharmacology
• Ion Channel Physiology
• Cardiac Electrophysiology

Background:

• The slow component of the delayed outward potassium current (IKs) plays a crucial role in cardiac repolarization.
• Inhibitors of IKs are of interest for managing cardiac arrhythmias, particularly those involving action potential prolongation.

Purpose of the Study:

• To characterize the novel IKs inhibitor, Chromanol HMR 1556.
• To evaluate the selectivity and efficacy of HMR 1556 on cardiac ion channels and action potential duration.

Main Methods:

• In vitro electrophysiology in Xenopus oocytes expressing human minK channels.
• Whole-cell patch-clamp recordings in isolated guinea pig and rat ventricular myocytes.
• Micropuncture and Langendorff perfusion techniques in guinea pig hearts to assess action potential parameters.

Main Results:

• HMR 1556 potently inhibited IKs with IC50 values of 120 nmol/l (oocytes) and 34 nmol/l (guinea pig myocytes).
• HMR 1556 showed high selectivity, with minimal effects on other tested K+ channels (Herg, Kv1.5, Kv1.3, Kir2.1), cationic channels (HCN2), and Ca2+ channels at relevant concentrations.
• In cardiac muscle, HMR 1556 significantly prolonged action potential duration (APD90), with effects maintained at physiological pacing rates.

Conclusions:

• Chromanol HMR 1556 is a potent and selective inhibitor of the cardiac IKs current.
• HMR 1556 effectively prolongs action potential duration, offering potential therapeutic applications in cardiac electrophysiology.