Abstract 1071: Expression and Pharmacological Correction of a LQT2 Mutant (hERG) Channel in Native Cardiomyocytes
Mutations within the human Ether-a-go-go Related Gene (hERG) encoding for the hERG K+ channel can lead to long QT syndrome type 2 (LQT2). Previous investigations have been performed using non-cardiac heterologous expression systems, and in mammalian systems most LQT2-linked missense mutations are trafficking deficient, with the channel protein failing to express at the cell surface membrane. Furthermore, the majority of these mutations can be induced to traffic to the cell surface by incubation in drugs (pharmacological correction), which has suggested that pharmacological correction might be developed as a clinical therapy. To further establish the feasibility of pharmacological correction in the heart, we demonstrated it in cardiomyocytes. We studied expression of WT-hERG and the trafficking-deficient LQT2-linked N470D-hERG mutation in HEK293 cells (using Superfect) or cardiomyocytes (using electroporation) isolated from 2-day-old mice. Using the patch clamp method to measure IhERG, peak tail current amplitude for N470D-hERG was reduced by 74% compared to WT-hERG in HEK293 cells (n=7–13 cells, p<0.05) and 94% in cardiomyocytes (n=6 –9 cells, p<0.05). HEK293 cells or cardiomyocytes expressing N470D-hERG were incubated with or without E-4031 (10 μM for 24 hrs) and E-4031 was washed out prior to recording IhERG. Incubation in E-4031 increased IhERG by 447% in HEK293 cells (n=9 –13 cells, p<0.05) and 1300% in cardomyocytes (n=6 –9 cells, p<0.05). We also measured the activation properties for IhERG. The potentials for half-maximal activation (V1/2) of WT-hERG expressed in HEK293 cells or cardiomyocytes were −7.5±1.8 and −12.9±1.1mV with slope factors of 6.7±0.2 and 6.2±0.3mV/e-foldΔ, respectively (n=5 cells each). The V1/2 for N470D-hERG after pharmacological correction in E-4031 was -38.1±2.4mV for HEK293 cells and -50.6±5.3mV for cardiomyocytes with slope factors of 7.1±0.3 and 9.9±1.1 mV/e-foldΔ, respectively (n=5 cells each). Our results demonstrate functional expression of WT- and N470D-hERG in a native cardiomyocyte system and that hERG channel properties are similar between expression systems. These are the first data to show pharmacological correction in cardiomyocytes.