Mechanism of Loss of Kv11.1 K+ Current in Mutant T421M-Kv11.1 Expressing Rat Ventricular Myocytes: Interaction of Trafficking and Gating
Background—Type 2 long QT syndrome (LQT2) involves mutations in the human ether a-go-go-related gene (hERG or KCNH2). T421M, a S1 domain mutation in the Kv11.1 channel protein, was identified in a resuscitated patient. We assessed its biophysical, protein trafficking and pharmacological mechanisms in adult rat ventricular myocytes (ARVMs).
Methods and Results—Isolated ARVMs were infected with WT- and T421M-Kv11.1 expressing adenovirus and analyzed using patch clamp, Western blot and confocal imaging techniques. Expression of WT- or T421M-Kv11.1 produced peak tail current (IKv11.1) of 8.78±1.18 and 1.91±0.22 pA/pF, respectively. Loss of mutant IKv11.1 resulted from, 1) a partially trafficking-deficient channel protein with reduced cell surface expression, and 2) altered channel gating with a positive shift in the voltage-dependence of activation and altered kinetics of activation and deactivation. Co-expression of WT+T421M-Kv11.1 resulted in heterotetrameric channels that remained partially trafficking-deficient with only a minimal increase in peak IKv11.1 density, whereas the voltage-dependence of channel gating became "WT-like". In the ARVM model, both WT- and T421M-Kv11.1 channels responded to β-adrenergic stimulation by increasing IKv11.1.
Conclusions—The T421M-Kv11.1 mutation caused a loss of IKv11.1 through interactions of abnormal protein trafficking and channel gating. Furthermore, for co-expressed WT+T421M-Kv11.1 channels, different dominant negative interactions govern protein trafficking and ion channel gating, and these are likely to be reflected in the clinical phenotype. Our results also show that WT and mutant Kv11.1 channels responded to β-adrenergic stimulation.
- Received May 14, 2012.
- Accepted October 22, 2012.
- Copyright © 2012, American Heart Association, Inc. All rights reserved. Unauthorized use prohibited