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

1. I-K8,I- the slow component of the delayed rectifier potassium current, f igures prominently in the repolarization of heart cells. The K+ channel gen e KvLQT1 is mutated in the heritable long QT (LQT) syndrome. Heterologous c oexpression of KvLQT1 and the accessory protein minK yields I-K8-like curre nt. Nevertheless, the links between KvLQT1 and cardiac I-K8 are largely inf erential. 2. Since the LQT syndrome mutant KvLQT1-G306R suppresses channel activity w hen coexpressed with wild-type KvLQT1 in a heterologous system, overexpress ion of this mutant in cardiomyocytes should reduce or eliminate native I-K8 if KvLQT1 is indeed the major molecular component of this current. To test this idea, we created the adenovirus AdRMGI-KvLQT1-G306R, which overexpres ses KvLQT1-G306R channels. 3. In > 60% of neonatal mouse myocytes, a sizable I-K8, could be measured u sing perforated-patch recordings (8.0 +/- 1.6 pA pF(-1), n = 13). I-K8 was increased by forskolin and blocked by clofilium or indapamide I,ut not by E -4031. While cells infected with a reporter virus expressing only green flu orescent protein (GFP) displayed I-K8 similar to that in uninfected cells, AdRMGI-KvLQT1-G306R-infected cells showed a significantly reduced I-K8 (2.4 +/- 1.1 pA pF(-1), 10, P< 0.01) when measured 60-72 h after infection. Sim ilar results were observed in adult guinea-pig myocytes (5.9 <plus/minus> 1 .2 pA pF(-1), n = 9, for control vs. 0.1 +/- 0.1 pA pF(-1), n = 5, for AdRM GI-KvLQT1-G306R-infected cells). 4. We conclude that KvLQT1 is the major molecular component of I-K8. Our re sults further establish a dominant-negative mechanism for the G306R LQT syn drome mutation.