Molecular Cloning and Functional Expression of the Equine K+ Channel KV11.1 (Ether à Go-Go-Related/KCNH2 Gene) and the Regulatory Subunit KCNE2 from Equine Myocardium.

Philip Juul Pedersen,Rikke Buhl,Kristian Lundgaard Poulsen,Dan Arne Klaerke,Kirsten Brolin Thomsen,Soren Grubb,Frank Hauser,Maria De Los Angeles Tejada,Emma Rie Olander,Kirstine Calloe,Diego Alvarez De La Rosa

doi:10.1371/journal.pone.0138320

Abstract

The KCNH2 and KCNE2 genes encode the cardiac voltage-gated K+ channel KV11.1 and its auxiliary β subunit KCNE2. KV11.1 is critical for repolarization of the cardiac action potential. In humans, mutations or drug therapy affecting the KV11.1 channel are associated with prolongation of the QT intervals on the ECG and increased risk of ventricular tachyarrhythmia and sudden cardiac death—conditions known as congenital or acquired Long QT syndrome (LQTS), respectively. In horses, sudden, unexplained deaths are a well-known problem. We sequenced the cDNA of the KCNH2 and KCNE2 genes using RACE and conventional PCR on mRNA purified from equine myocardial tissue. Equine KV11.1 and KCNE2 cDNA had a high homology to human genes (93 and 88%, respectively). Equine and human KV11.1 and KV11.1/KCNE2 were expressed in Xenopus laevis oocytes and investigated by two-electrode voltage-clamp. Equine KV11.1 currents were larger compared to human KV11.1, and the voltage dependence of activation was shifted to more negative values with V1/2 = -14.2±1.1 mV and -17.3±0.7, respectively. The onset of inactivation was slower for equine KV11.1 compared to the human homolog. These differences in kinetics may account for the larger amplitude of the equine current. Furthermore, the equine KV11.1 channel was susceptible to pharmacological block with terfenadine. The physiological importance of KV11.1 was investigated in equine right ventricular wedge preparations. Terfenadine prolonged action potential duration and the effect was most pronounced at slow pacing. In conclusion, these findings indicate that horses could be disposed to both congenital and acquired LQTS.

Highlights

In equine medicine, sudden deaths are a well-known problem and often the cause of death cannot be determined by necropsy [1]
Equine currents were larger compared to human KV11.1 and the voltage dependence of activation was shifted to more negative values
The onset of inactivation was slower in equine KV11.1 compared to human KV11.1, and we are speculating whether these differences in kinetics can contribute to the increase in KV11.1 current

Summary

Introduction

Sudden deaths are a well-known problem and often the cause of death cannot be determined by necropsy [1]. SCD in athletes has been linked to the Long QT Syndrome (LQTS) [4]. Repolarization of the cardiac action potential in larger mammals, including humans and horses, has been shown to be dependent on the rapid and slow activating delayed rectifier K+ currents, IKr and IKs [6,9,10]. Loss of function mutations in the genes encoding proteins mediating IKr or IKs are common causes of congenital LQTS in humans and pharmaceutical blockage of IKr is a well described cause of acquired LQTS. Acquired LQTS might be of relevance to equine patients as horses are often treated with drugs known to prolong cardiac repolarization in other species, including quinidine, cisapride, erythromycin, and trimethoprim-sulfamethoxazole

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