Jo Sooyeon, Bean Bruce P
Department of Neurobiology, Harvard Medical School, Boston Massachusetts.
Department of Neurobiology, Harvard Medical School, Boston Massachusetts
Mol Pharmacol. 2017 Apr;91(4):277-286. doi: 10.1124/mol.116.106401. Epub 2017 Jan 24.
Lacosamide is an antiseizure agent that targets voltage-dependent sodium channels. Previous experiments have suggested that lacosamide is unusual in binding selectively to the slow-inactivated state of sodium channels, in contrast to drugs like carbamazepine and phenytoin, which bind tightly to fast-inactivated states. Using heterologously expressed human Nav1.7 sodium channels, we examined the state-dependent effects of lacosamide. Lacosamide induced a reversible shift in the voltage dependence of fast inactivation studied with 100-millisecond prepulses, suggesting binding to fast-inactivated states. Using steady holding potentials, lacosamide block was very weak at -120 mV (3% inhibition by 100 M lacosamide) but greatly enhanced at -80 mV (43% inhibition by 100 M lacosamide), where there is partial fast inactivation but little or no slow inactivation. During long depolarizations, lacosamide slowly (over seconds) put channels into states that recovered availability slowly (hundreds of milliseconds) at -120 mV. This resembles enhancement of slow inactivation, but the effect was much more pronounced at -40 mV, where fast inactivation is complete, but slow inactivation is not, than at 0 mV, where slow inactivation is maximal, more consistent with slow binding to fast-inactivated states than selective binding to slow-inactivated states. Furthermore, inhibition by lacosamide was greatly reduced by pretreatment with 300 M lidocaine or 300 M carbamazepine, suggesting that lacosamide, lidocaine, and carbamazepine all bind to the same site. The results suggest that lacosamide binds to fast-inactivated states in a manner similar to other antiseizure agents but with slower kinetics of binding and unbinding.
拉科酰胺是一种作用于电压依赖性钠通道的抗癫痫药物。先前的实验表明，与卡马西平和苯妥英等紧密结合快速失活状态的药物不同，拉科酰胺的独特之处在于它选择性地结合钠通道的缓慢失活状态。我们利用异源表达的人Nav1.7钠通道，研究了拉科酰胺的状态依赖性效应。拉科酰胺通过100毫秒预脉冲研究诱导快速失活的电压依赖性发生可逆性改变，提示其与快速失活状态结合。使用稳定的钳制电位，拉科酰胺在-120 mV时阻断作用非常弱（100 μM拉科酰胺抑制3%），但在-80 mV时显著增强（100 μM拉科酰胺抑制43%），此时存在部分快速失活但几乎没有缓慢失活。在长时间去极化过程中，拉科酰胺缓慢地（数秒内）使通道进入在-120 mV时缓慢恢复可用状态（数百毫秒）的状态。这类似于缓慢失活的增强，但在-40 mV时效应更为明显，此时快速失活完全但缓慢失活不完全，而在0 mV时缓慢失活最大，这表明拉科酰胺与快速失活状态的缓慢结合比选择性结合缓慢失活状态更一致。此外，用300 μM利多卡因或300 μM卡马西平预处理可大大降低拉科酰胺的抑制作用, 提示拉科酰胺、利多卡因和卡马西平都结合于同一部位。结果表明，拉科酰胺以与其他抗癫痫药物相似的方式结合快速失活状态，但结合和解离的动力学较慢。
