An R H, Wang X L, Kerem B, Benhorin J, Medina A, Goldmit M, Kass R S
Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
Circ Res. 1998 Jul 27;83(2):141-6. doi: 10.1161/01.res.83.2.141.
The congenital long-QT syndrome (LQT), an inherited cardiac arrhythmia characterized in part by prolonged ventricular repolarization, has been linked to 5 loci, 4 of which have been shown to harbor genes that encode ion channels. Previously studied LQT-3 mutations of SCN5A (or hH1), the gene that encodes the human Na+ channel alpha-subunit, have been shown to encode voltage-gated Na+ channels that reopen during prolonged depolarization and hence directly contribute to the disease phenotype: delayed repolarization. Here, we report the functional consequences of a novel SCN5A mutation discovered in an extended LQT family. The mutation, a single A-->G base substitution at nucleotide 5519 of the SCN5A cDNA, is expected to cause a nonconservative change from an aspartate to a glycine at position 1790 (D1790G) of the SCN5A gene product. We investigated ion channel activity in human embryonic kidney (HEK 293) cells transiently transfected with wild-type (hH1) or mutant (D1790G) cDNA alone or in combination with cDNA encoding the human Na+ channel beta1-subunit (hbeta1) using whole-cell patch-clamp procedures. Heteromeric channels formed by coexpression of alpha- and beta1-subunits are affected: steady-state inactivation is shifted by -16 mV, but there is no D1790G-induced sustained inward current. This effect is independent of the beta1-subunit isoform. We find no significant effect of D1790G on the biophysical properties of monomeric alpha- (hH1) channels. We conclude that the effects of the novel LQT-3 mutation on inactivation of heteromeric channels are due to D1790G-induced changes in alpha- and beta1-interactions.
先天性长QT综合征（LQT）是一种遗传性心律失常，部分特征为心室复极延长，与5个基因座相关，其中4个已被证明含有编码离子通道的基因。先前研究的编码人类钠通道α亚基的基因SCN5A（或hH1）的LQT - 3突变，已被证明可编码在长时间去极化期间重新开放的电压门控钠通道，因此直接导致疾病表型：复极延迟。在此，我们报告了在一个扩展性LQT家族中发现的一种新型SCN5A突变的功能后果。该突变是SCN5A cDNA核苷酸5519处的单个A→G碱基替换，预计会导致SCN5A基因产物第1790位（D1790G）的天冬氨酸变为甘氨酸，这是一种非保守性变化。我们使用全细胞膜片钳技术，研究了单独瞬时转染野生型（hH1）或突变型（D1790G）cDNA，或与编码人类钠通道β1亚基（hβ1）的cDNA组合的人类胚胎肾（HEK 293）细胞中的离子通道活性。由α和β1亚基共表达形成的异源通道受到影响：稳态失活向负向移动了16 mV，但没有D1790G诱导的持续内向电流。这种效应与β1亚基异构体无关。我们发现D1790G对单体α（hH1）通道的生物物理特性没有显著影响。我们得出结论，这种新型LQT - 3突变对异源通道失活的影响是由于D1790G诱导的α和β1相互作用的变化。
