Gibbs J W, Sombati S, DeLorenzo R J, Coulter D A
Department of Neurology, Medical College of Virginia, Richmond, USA.
Epilepsia. 2000;41(S1):10-6. doi: 10.1111/j.1528-1157.2000.tb02164.x.
This study was undertaken to evaluate the effects of topiramate (TPM) on excitatory amino acid-evoked currents.
Kainate and N-methyl-D-aspartate (NMDA) were applied to cultured rat hippocampal neurons by using a concentration-clamp apparatus to selectively activate the AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)/kainate and NMDA receptor subtypes, respectively. The evoked membrane currents were recorded by using perforated-patch whole-cell voltage-clamp techniques.
TPM partially blocked kainate-evoked currents with an early-onset reversible phase (phase I) and a late-onset phase (phase II) that occurred after a 10- to 20-min delay and did not reverse during a 2-h washout period. Application of dibutyryl cyclic adenosine monophosphate (cAMP; 2 mM) during washout after phase II block enhanced reversal, with the kainate current amplitude being restored by approximately 50%. Phase II but not phase I block was prevented by prior application of okadaic acid (1 microM), a broad-spectrum phosphatase inhibitor, suggesting that phase II block may be mediated through interactions with intracellular intermediaries that alter the phosphorylation state of kainate-activated channels. Topiramate at 100 microM blocked kainate-evoked currents by 90% during phase II, but had no effect on NMDA-evoked currents. The median inhibitory concentration (IC50) values for phase I and II block of kainate currents were 1.6 and 4.8 microM, respectively, which are within the range of free serum levels of TPM in patients.
The specific blockade of the kainate-induced excitatory conductance is consistent with the ability of TPM to reduce neuronal excitability and could contribute to the anticonvulsant efficacy of this drug.
本研究旨在评估托吡酯（TPM）对兴奋性氨基酸诱发电流的影响。
通过使用浓度钳装置将海人酸和N-甲基-D-天冬氨酸（NMDA）分别施加于培养的大鼠海马神经元，以选择性激活α-氨基-3-羟基-5-甲基异恶唑-4-丙酸（AMPA）/海人酸和NMDA受体亚型。使用穿孔膜片全细胞电压钳技术记录诱发的膜电流。
TPM部分阻断海人酸诱发的电流，存在一个早期发作的可逆阶段（I期）和一个延迟10至20分钟后出现的晚期发作阶段（II期），且在2小时的洗脱期内不逆转。在II期阻断后的洗脱过程中应用二丁酰环磷腺苷（cAMP；2 mM）可增强逆转，海人酸电流幅度恢复约50%。预先应用广谱磷酸酶抑制剂冈田酸（1 microM）可预防II期而非I期阻断，这表明II期阻断可能是通过与改变海人酸激活通道磷酸化状态的细胞内中介物相互作用介导的。100 microM的托吡酯在II期可将海人酸诱发的电流阻断90%，但对NMDA诱发的电流无影响。海人酸电流I期和II期阻断的半数抑制浓度（IC50）值分别为1.6和4.8 microM，处于TPM在患者血清中的游离水平范围内。
海人酸诱导的兴奋性电导的特异性阻断与TPM降低神经元兴奋性的能力一致，可能有助于该药物的抗惊厥疗效。
