**Background**
Cardiac arrhythmias, particularly atrial fibrillation, are characterized by abnormal electrical activity in the heart, often involving the dysfunction of ion channels. The regulation of action potential duration and refractoriness in the atria is heavily dependent on the activity of voltage-gated sodium (Na+) channels and potassium (K+) channels. Among these, the Kv1.5 channel plays a critical role in the ultra-rapid delayed rectifier potassium current, making it a primary target for pharmacological intervention to restore normal sinus rhythm. Developing agents that can selectively target atrial channels while minimizing effects on ventricular tissue is essential for safe and effective antiarrhythmic therapy. In this context, we will introduce a mixed voltage- and frequency-dependent channel blocker – Vernakalant.
**Definition**
Vernakalant hydrochloride is a mixed voltage- and frequency-dependent Na+ and atria-preferred K+ channel blocker. According to the Vernakalant description, it exhibits specific inhibitory activity against Kv1.5 channels with an IC50 value of 13.35±0.93 μM for the wild-type channel.
**In Vitro Studies**
The Vernakalant biological activity is characterized by its ability to block Kv1.5 channels in a manner mediated by channel activation. Specifically, Vernakalant causes a rapid onset of block upon depolarization, with little evidence of resting or “tonic” block. In Vernakalant in vitro experiments, the application of 10 μM Vernakalant results in a rapid block after channel opening, quickly reaching a steady-state current level. Further investigation into the molecular basis of its binding reveals that the potency is highly dependent on specific amino acid residues. For instance, the I502A mutation leads to a 25-fold decrease in potency, with the IC50 increasing to 329±19 μM compared to the control IC50 of 13.4±0.9 μM. Other mutations, such as V505A, I508A, T480A, and C500A, showed lesser reductions in potency, ranging between 3- and 4-fold. Additionally, the I508F and T479A mutant Kv1.5 channels exhibited fractional blocks of 0.61±0.03 μM and 1.63±0.09 μM, respectively. The I508Y mutation increased the IC50 to 24.7 μM. In conclusion, Vernakalant is a potent and selective blocker of atrial K+ channels, specifically targeting the Kv1.5 channel to modulate cardiac electrical activity.
Keywords
Vernakalant, 748810-28-8, RSD1235, RSD 1235, RSD-1235, Potassium Channel, KcsA, Inhibitor, inhibitor, inhibit
References
[1] Eldstrom J, et al. The molecular basis of high-affinity binding of the antiarrhythmic compound Vernakalant (RSD1235) to Kv1.5 channels. Mol Pharmacol. 2007 Dec;72(6):1522-34.
[2] Chiba T, et al. Influences of rapid pacing-induced electrical remodeling on pharmacological manipulation of the atrial refractoriness in rabbits. J Pharmacol Sci. 2016 Mar;130(3):170-6.