Noguchi T, Ishii K, Ohtubo Y, Shuto S, Ono S, Matsuda A, Yoshii K
Department of Biochemical Engineering and Science, Kyushu Institute of Technology, Iizuka, Japan.
Synapse. 1999 Feb;31(2):87-96. doi: 10.1002/(SICI)1098-2396(199902)31:2<87::AID-SYN1>3.0.CO;2-H.
We investigated the blocking effect of the conformationally restricted analogs of milnacipran on NMDA receptors by recording the whole-cell currents of Xenopus oocytes injected with rat brain mRNA and the single channel currents of cultured hippocampal neurons under voltage-clamp conditions. Their protective effect against excitotoxicity was also investigated on cultured cortex neurons. All conformationally restricted analogs examined blocked activated NMDA receptors, though their structures were quite different from known NMDA receptor blockers. The analogs with a (1S, 2R, 1'S)-configuration such as PPDC ((1S, 2R)-1-phenyl-2[(S)-1-aminopropyl]-N,N-diethylcyclopropanecarboxamide+ ++) had lower IC50 values than those with other configurations. The empirical Hill coefficients for each compound were close to unity, indicating a 1:1 stoichiometry for the block. PPDC decreased the maximum responses to both N-methyl D-aspartate (NMDA) and glycine without altering their dissociation constants. The blocking effect was enhanced on hyperpolarization. PPDC had no effects on other glutamate receptor subtypes (AMPA, kainate, and metabotropic glutamate receptors) or other neurotransmitter receptors (GABA(A), 5HT2C, and AChM1 receptors) produced by the oocytes. PPDC decreased the mean open time of NMDA receptors without decreasing their elementary conductance. The microscopic blocking rate constant was 2.8x10(7) M(-1)s(-1). The macroscopic unblocking rate constant of PPDC was much faster than that of MK-801. Only the analogs with the (1S, 2R, 1'S)-configuration protected the cultures against NMDA-induced neurotoxicity, though they failed to protect against kainate-induced neurotoxicity. These results show that conformationally restricted analogs, at least PPDC, selectively blocked open channels of NMDA receptors.
我们通过在电压钳制条件下记录注射大鼠脑mRNA的非洲爪蟾卵母细胞的全细胞电流以及培养的海马神经元的单通道电流，研究了米那普明构象受限类似物对NMDA受体的阻断作用。还在培养的皮层神经元上研究了它们对兴奋性毒性的保护作用。所有检测的构象受限类似物均能阻断激活的NMDA受体，尽管它们的结构与已知的NMDA受体阻断剂有很大不同。具有(1S, 2R, 1'S)构型的类似物，如PPDC（(1S, 2R)-1-苯基-2[(S)-1-氨丙基]-N,N-二乙基环丙烷甲酰胺）的IC50值低于其他构型的类似物。每种化合物的经验希尔系数接近1，表明阻断的化学计量比为1:1。PPDC降低了对N-甲基-D-天冬氨酸（NMDA）和甘氨酸的最大反应，而不改变它们的解离常数。超极化时阻断作用增强。PPDC对卵母细胞产生的其他谷氨酸受体亚型（AMPA、海人藻酸和代谢型谷氨酸受体）或其他神经递质受体（GABA(A)、5HT2C和AChM1受体）无影响。PPDC降低了NMDA受体的平均开放时间，而不降低其基本电导。微观阻断速率常数为2.8×10(7) M(-1)s(-1)。PPDC的宏观解除阻断速率常数比MK-801快得多。只有具有(1S, 2R, 1'S)构型的类似物能保护培养物免受NMDA诱导的神经毒性，尽管它们不能保护免受海人藻酸诱导的神经毒性。这些结果表明，构象受限类似物，至少PPDC，选择性地阻断NMDA受体的开放通道。
