Mutations in the human ether-a-go-go related gene 1 (hERG) are linked to long QT syndrome type 2 (LQT2). hERG encodes the pore-forming α-subunits that co-assemble to form the rapidly activating delayed rectifier K+ current (IKr) in the heart. LQT2-linked missense mutatations have been extensively studied in non-cardiac heterologous expression systems where biogenic (protein trafficking) and biophysical (gating, permeation) abnormalities have been postulated to underlie the loss-of-function phenotype associated with LQT2 channels. Little is known about the properties of LQT2-linked hERG channel proteins in native cardiomyocyte systems. In this study, we expressed WT-hERG and three LQT2-linked mutations in neonatal mouse cardiomyocytes and studied their electrophysiological and biochemical properties. Compared to WT-hERG channels, the LQT2 missense mutations G601S- and N470D-hERG exhibited altered protein trafficking and underwent pharmacological correction, and N470D-hERG gated at more negative voltages. The ΔY475-hERG deletion mutation trafficked similar to WT-hERG, gated at more negative voltages and had rapid deactivation kinetics, and these properties were confirmed in both neonatal mouse cardiomyocyte and HEK293 cell expression systems. Differences between the cardiomyocytes and HEK293 cell expression systems were that hERG current densities were reduced 10-fold and deactivation kinetics were accelerated 1.5 to 2-fold in the neonatal mouse cardiomyocytes. An important finding of this work is that pharmacological correction of trafficking-deficient LQT2 mutations, as a potential innovative approach to therapy, is possible in native cardiac tissue.
- mouse cardiomyocytes
- protein trafficking
- Copyright © 2010, American Journal of Physiology - Heart and Circulatory Physiology