Abstract 15282: β-adrenergic Stimulation Increases Wild Type and LQT2 Mutant Kv11.1 Current in Adult Rat Ventricular Myocyte Expression Model
KCNH2 encodes the α-subunits of Kv11.1 K+ channels that mediate rapidly activating delayed rectifier K+ current (IKr ). Mutations in KCNH2 resulting in type 2 long QT syndrome (LQT2) cause variable loss of IKr. LQT2-triggered arrhythmias may be precipitated during physical or emotional stress, suggesting a link between adrenergic stimulation and Kv11.1 channel activity. However, β-adrenergic (βAR) regulation of WT Kv11.1 channels is controversial, and the effects of βAR stimulation on LQT2-causing mutant channels have not been studied. T421M is a missense mutation in the S1-transmembrane domain of Kv11.1 channels and was identified in a 33 yo patient resuscitated from near sudden death episode triggered by emotional stress. We investigated the disease mechanism and βAR regulation of T421M channels compared to WT channels expressed in adult rat ventricular myocytes (ARVM). ARVM were isolated by enzymatic dissociation, infected with adenovirus expressing WT or T421M genes, and cultured for 4 days. Cultured ARVM lack native IKr. Confocal imaging showed reduced expression of T421M channels at the cell surface (mean fluorescence intensity ratio at cell edges compared to cell middle was 6.2±1.8 for WT and 1.8±0.5 for T421). Western blot analysis showed diminished mature (155 kDa) protein for T421M compared to WT, indicating a partially trafficking-deficient phenotype. Whole-cell patch clamp of WT or T421M infected ARVM produced Kv11.1 current (IKv11.1) with peak tail amplitudes of 8.78±1.18 and 1.91±0.22 pA/pF (mean±SEM, p<0.05, n=12), respectively. Following superfusion with the βAR agonist isoproterenol (10 μM), peak tail IKv11.1 for WT and T421M increased by 32% (p<0.05) and 22% (p<0.05, n=6), respectively. The effect of isoproterenol was partially reversed with washout for WT but not T421M channels. Our results demonstrate a partially trafficking-deficient phenotype of T421M channels. More importantly, we demonstrate for the first time βAR responsiveness for heterologously expressed mutant and WT Kv11.1 channels studied in native adult cardiomyocytes. Our results show a direct modulatory role of Kv11.1 channels by βAR stimulation to potentially contribute to the altered arrhythmogenic substrate in LQT2 patients.
- Beta-adrenergic receptor agonists
- Ion channels
- Potassium channel
- Arrhythmias, treatment of
- Myocyte electrophysiology
- © 2011 by American Heart Association, Inc.