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

Ronald A. Li, Junichiro Miake, Uta C. Hoppe, David C. Johns, Eduardo Marbán and H. Bradley Nuss

1. I_Ks, 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.
2. 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.
3. 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).
4. 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.

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