Dryer S E
Department of Physiology, University of Colorado School of Medicine, Denver 80262.
Brain Res. 1988 Mar 8;443(1-2):173-82. doi: 10.1016/0006-8993(88)91610-1.
The characteristics of excitatory amino acid-evoked currents and of excitatory synaptic events have been examined in lamprey Müller neurons using voltage clamp and current clamp recording techniques. Application of glutamate evoked depolarizations associated with a decrease in input resistance. The reversal potential of the responses was -35 mV. Under voltage clamp conditions, a series of excitatory amino acid agonists evoked inward currents associated with little or no increase in baseline current noise. The order of potency of the excitatory amino acid agonists was quisqualate greater than kainate greater than glutamate greater than aspartate, while N-methyl-D-aspartic acid (NMDA) was inactive. Inward currents evoked by glutamate, as well as by kainate and quisqualate were attenuated reversibly by 1 mM kynurenic acid (KYN). In contrast, glutamate-evoked currents were not affected by 100 microM D(-)-2-amino-5-phosphonovaleric acid (APV), a selective NMDA antagonist. Spontaneously occurring and stimulus-evoked excitatory postsynaptic events were antagonized reversibly by 1 mM KYN. At this concentration, KYN had no effect on membrane potential, input resistance, or excitability of the cells. In contrast, excitatory postsynaptic currents were unaffected by APV. It is concluded that both glutamate responses and excitatory synaptic transmission in lamprey Müller neurons are mediated by non-NMDA-type receptors and that these receptors are associated with ionic channels with a low elementary conductance. The combined pharmacological and biophysical characteristics of these responses are therefore different from those previously reported in other preparations. Spontaneous (but not stimulus-evoked) inhibitory synaptic events in Müller neurons were blocked reversibly by 1 mM KYN but not by 100 microM APV, suggesting that excitation of interneurons inhibitory to Müller cells was also mediated by non-NMDA receptors.
利用电压钳和电流钳记录技术，在七鳃鳗缪勒神经元中研究了兴奋性氨基酸诱发电流和兴奋性突触事件的特征。应用谷氨酸会诱发去极化，同时伴有输入电阻降低。反应的反转电位为 -35 mV。在电压钳条件下，一系列兴奋性氨基酸激动剂诱发内向电流，且基线电流噪声几乎没有增加或没有增加。兴奋性氨基酸激动剂的效力顺序为：quisqualate大于海人藻酸大于谷氨酸大于天冬氨酸，而N-甲基-D-天冬氨酸（NMDA）无活性。谷氨酸、海人藻酸和quisqualate诱发的内向电流可被1 mM犬尿喹啉酸（KYN）可逆性减弱。相反，谷氨酸诱发的电流不受100 μM D(-)-2-氨基-5-磷酸缬氨酸（APV，一种选择性NMDA拮抗剂）的影响。自发出现的和刺激诱发的兴奋性突触后事件可被1 mM KYN可逆性拮抗。在此浓度下，KYN对细胞的膜电位、输入电阻或兴奋性无影响。相反，兴奋性突触后电流不受APV影响。得出的结论是，七鳃鳗缪勒神经元中的谷氨酸反应和兴奋性突触传递均由非NMDA型受体介导，且这些受体与低单通道电导的离子通道相关。因此，这些反应的联合药理学和生物物理学特征与先前在其他标本中报道的不同。缪勒神经元中的自发（但非刺激诱发）抑制性突触事件可被1 mM KYN可逆性阻断，但不能被100 μM APV阻断，这表明对缪勒细胞具有抑制作用的中间神经元的兴奋也由非NMDA受体介导。
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