Department of Pharmacology, Vanderbilt University, Nashville, TN 37232-0275, USA.
Br J Pharmacol. 2010 Nov;161(6):1414-26. doi: 10.1111/j.1476-5381.2010.00976.x.
Mutations of SCN1A, the gene encoding the pore-forming subunit of the voltage-gated sodium channel Na(V) 1.1, have been associated with a spectrum of genetic epilepsies and a familial form of migraine. Several mutant Na(V) 1.1 channels exhibit increased persistent current due to incomplete inactivation and this biophysical defect may contribute to altered neuronal excitability in these disorders. Here, we investigated the ability of ranolazine to preferentially inhibit increased persistent current evoked by mutant Na(V) 1.1 channels.
Human wild-type (WT) and mutant Na(V) 1.1 channels were expressed heterologously in human tsA201 cells and whole-cell patch clamp recording was used to assess tonic and use-dependent ranolazine block.
Ranolazine (30 µM) did not affect WT Na(V) 1.1 channel current density, activation or steady-state fast inactivation but did produce mild slowing of recovery from inactivation. Ranolazine blocked persistent current with 16-fold selectivity over tonic block of peak current and 3.6-fold selectivity over use-dependent block of peak current. Similar selectivity was observed for ranolazine block of increased persistent current exhibited by Na(V) 1.1 channel mutations representing three distinct clinical syndromes, generalized epilepsy with febrile seizures plus (R1648H, T875M), severe myoclonic epilepsy of infancy (R1648C, F1661S) and familial hemiplegic migraine type 3 (L263V, Q1489K). In vitro application of achievable brain concentrations (1, 3 µM) to cells expressing R1648H channels was sufficient to suppress channel activation during slow voltage ramps, consistent with inhibition of persistent current.
Our findings support the feasibility of using selective suppression of increased persistent current as a potential new therapeutic strategy for familial neurological disorders associated with certain sodium channel mutations.
电压门控钠离子通道 Na(V)1.1 的编码基因 SCN1A 的突变与一系列遗传性癫痫和家族性偏头痛有关。几种突变的 Na(V)1.1 通道由于不完全失活而表现出增加的持续电流，这种生物物理缺陷可能导致这些疾病中神经元兴奋性的改变。在这里，我们研究了雷诺嗪优先抑制突变的 Na(V)1.1 通道诱发的增加的持续电流的能力。
将人野生型（WT）和突变型 Na(V)1.1 通道异源表达于人 tsA201 细胞中，并使用全细胞膜片钳记录来评估强直和使用依赖性雷诺嗪阻断。
雷诺嗪（30μM）不影响 WT Na(V)1.1 通道电流密度、激活或稳态快速失活，但确实导致失活恢复轻度减慢。雷诺嗪对持续电流的阻断具有 16 倍的选择性，相对于峰值电流的强直阻断，3.6 倍的选择性，相对于峰值电流的使用依赖性阻断。在代表三种不同临床综合征的 Na(V)1.1 通道突变体中观察到雷诺嗪对增加的持续电流的阻断具有相似的选择性，这些突变体包括全面性癫痫伴热性惊厥附加症（R1648H、T875M）、婴儿严重肌阵挛性癫痫（R1648C、F1661S）和家族性偏瘫性偏头痛 3 型（L263V、Q1489K）。在表达 R1648H 通道的细胞中，应用可达到的脑浓度（1、3μM）进行体外应用足以在缓慢电压斜坡期间抑制通道激活，与持续电流的抑制一致。
我们的发现支持选择性抑制增加的持续电流作为治疗与某些钠离子通道突变相关的家族性神经疾病的潜在新治疗策略的可行性。
