Functional consequences of the arrhythmogenic G306R KvLQT1 K + channel mutant probed by viral gene transfer in cardiomyocytes

IKs , the slow component of the delayed rectifier potassium current, figures prominently in the repolarization of heart cells. The K + channel gene KvLQT1 is mutated in the heritable long QT (LQT) syndrome. Heterologous coexpression of KvLQT1 and the accessory protein minK yields an I Ks ‐like current. Nevertheless, the links between KvLQT1 and cardiac I Ks are largely inferential. Since the LQT syndrome mutant KvLQT1‐G306R suppresses channel activity when coexpressed with wild‐type KvLQT1 in a heterologous system, overexpression of this mutant in cardiomyocytes should reduce or eliminate native I Ks if KvLQT1 is indeed the major molecular component of this current. To test this idea, we created the adenovirus AdRMGI‐KvLQT1‐G306R, which overexpresses KvLQT1‐G306R channels. In > 60 % of neonatal mouse myocytes, a sizable I Ks could be measured using perforated‐patch recordings (8.0 ± 1.6 pA pF −1 , n = 13). I Ks was increased by forskolin and blocked by clofilium or indapamide but not by E‐4031. While cells infected with a reporter virus expressing only green fluorescent protein (GFP) displayed I Ks similar to that in uninfected cells, AdRMGI‐KvLQT1‐G306R‐infected cells showed a significantly reduced I Ks (2.4 ± 1.1 pA pF −1 , n = 10, P < 0.01) when measured 60‐72 h after infection. Similar results were observed in adult guinea‐pig myocytes (5.9 ± 1.2 pA pF −1 , n = 9, for control vs. 0.1 ± 0.1 pA pF −1 , n = 5, for AdRMGI‐KvLQT1‐G306R‐infected cells). We conclude that KvLQT1 is the major molecular component of I Ks . Our results further establish a dominant‐negative mechanism for the G306R LQT syndrome mutation.