Bertolino M, Vicini S
FIDIA-Georgetown Institute for the Neurosciences, Georgetown University Medical School, Washington, DC 20007.
Mol Pharmacol. 1988 Aug;34(2):98-103.
Single-channel currents were recorded by means of the patch clamp method in outside-out patches excised from rat cortical neurons in primary culture. The excitatory amino acid N-methyl-D-aspartic acid activated mainly 40-50 pS conductance channels. Channel opening durations were characterized by a series of rapid openings and closures induced by the presence of Mg2+ ions. This inhibitory effect was voltage dependent. Strychnine, the antagonist of the glycine-gated Cl- channels, blocks the N-methyl-D-aspartic acid-activated cationic channel in cultured rat cortical neurons. Strychnine action is voltage dependent and it is not counteracted by ethylenediaminetetraacetic acid, ruling out Mg2+ contamination of strychnine. It has been reported recently that glycine increases the rate of openings of N-methyl-D-aspartic acid-activated channels. This action is not affected by the presence of strychnine. Our results show that 1) Mg2+ and strychnine have an apparently similar intermediate blocking action on the NMDA-activated channels, 2) strychnine presumably acts as a sequential open channel blocker producing a different type of block compared with the one reported for Mg2+ ions, and 3) the lack of effect of strychnine on the glycine potentiation of the N-methyl-D-aspartic acid response indicates that this alkaloid does not competitively antagonize glycine but acts as an open channel blocker.
采用膜片钳技术，在从原代培养的大鼠皮层神经元上切下的外侧膜片上记录单通道电流。兴奋性氨基酸N-甲基-D-天冬氨酸主要激活40 - 50 pS电导的通道。通道开放持续时间的特征是由Mg2+离子的存在诱导的一系列快速开放和关闭。这种抑制作用是电压依赖性的。士的宁是甘氨酸门控Cl-通道的拮抗剂，可阻断培养的大鼠皮层神经元中N-甲基-D-天冬氨酸激活阳离子通道。士的宁的作用是电压依赖性的，且不受乙二胺四乙酸的拮抗，排除了士的宁中Mg2+污染的可能性。最近有报道称，甘氨酸可增加N-甲基-D-天冬氨酸激活通道的开放速率。这一作用不受士的宁存在的影响。我们的结果表明：1）Mg2+和士的宁对NMDA激活通道具有明显相似的中间阻断作用；2）士的宁可能作为一种序列性开放通道阻断剂，与报道的Mg2+离子产生的阻断类型不同；3）士的宁对甘氨酸增强N-甲基-D-天冬氨酸反应无影响，表明该生物碱不是竞争性拮抗甘氨酸，而是作为一种开放通道阻断剂起作用。
