Pisani Antonio, Bonsi Paola, Martella Giuseppina, De Persis Cristiano, Costa Cinzia, Pisani Francesco, Bernardi Giorgio, Calabresi Paolo
Clinica Neurologica, Dipartimento di Neuroscienze, Università di Roma "Tor Vergata,", Rome, Italy.
Epilepsia. 2004 Jul;45(7):719-28. doi: 10.1111/j.0013-9580.2004.02204.x.
Alterations in neuronal calcium (Ca2+) homeostasis are believed to play an essential role in the generation and propagation of epileptiform events. Levetiracetam (LEV) and lamotrigine (LTG), novel antiepileptic drugs (AEDs), were tested on epileptiform events and the corresponding elevations in intracellular Ca2+ concentration ([Ca2+]i) recorded from rat neocortical slices.
Electrophysiological recordings were performed from single pyramidal neurons from a slice preparation. Spontaneous epileptiform events consisting of long-lasting, repetitive paroxysmal depolarization shifts (PDSs) and interictal spike activity were induced by reducing the magnesium concentration from the solution and by adding bicuculline and 4-aminopyridine. Simultaneously, microfluorimetric measurements of [Ca2+]i were performed. Optical imaging with Ca2+ indicators revealed a close correlation between Ca2+ transients and epileptiform events.
Both LEV and LTG were able to reduce both amplitude and duration of PDSs, as well as the concomitant elevation in [Ca2+]i, in a dose-dependent fashion. Whole-cell patch-clamp recordings from isolated neocortical neurons revealed that LEV significantly reduced N-, and partially P/Q-type high-voltage-activated (HVA) Ca2+ currents, whereas sodium currents were unaffected. Interestingly, the inhibitory effects of LEV were mimicked and occluded by LTG or by a combination of omega-conotoxin GVIA and omega-agatoxin IVA, selective blockers of N- and P/Q-type HVA channels, respectively, suggesting a common site of action for these AEDs.
These results demonstrate that large, transient elevations in neuronal [Ca2+]i correlate to epileptiform discharges. The antagonistic effects of LEV and LTG on [Ca2+]i overload might represent the basis for their anticonvulsant efficacy and could preserve neuronal viability.
神经元钙（Ca2+）稳态的改变被认为在癫痫样事件的产生和传播中起重要作用。对新型抗癫痫药物（AEDs）左乙拉西坦（LEV）和拉莫三嗪（LTG）进行了测试，观察其对癫痫样事件以及从大鼠新皮质切片记录到的细胞内Ca2+浓度（[Ca2+]i）相应升高的影响。
从切片标本中的单个锥体神经元进行电生理记录。通过降低溶液中的镁浓度并添加荷包牡丹碱和4-氨基吡啶，诱导出由持久、重复性阵发性去极化移位（PDSs）和发作间期棘波活动组成的自发性癫痫样事件。同时，进行[Ca2+]i的微荧光测量。用Ca2+指示剂进行光学成像显示Ca2+瞬变与癫痫样事件之间密切相关。
LEV和LTG均能以剂量依赖性方式降低PDSs的幅度和持续时间以及伴随的[Ca2+]i升高。从分离的新皮质神经元进行的全细胞膜片钳记录显示，LEV显著降低N型以及部分P/Q型高电压激活（HVA）Ca2+电流，而钠电流不受影响。有趣的是，LTG或ω-芋螺毒素GVIA和ω-阿加毒素IVA（分别为N型和P/Q型HVA通道的选择性阻滞剂）的组合模拟并阻断了LEV的抑制作用，提示这些AEDs有共同的作用位点。
这些结果表明，神经元[Ca2+]i的大幅短暂升高与癫痫样放电相关。LEV和LTG对[Ca2+]i过载的拮抗作用可能是其抗惊厥疗效的基础，并可能维持神经元的活力。
