Thomas N K, Hawkins L M, Miller J C, Troop H M, Roberts P J, Jane D E
Department of Pharmacology, School of Medical Sciences, University of Bristol, UK.
Neuropharmacology. 1998 Oct-Nov;37(10-11):1223-37. doi: 10.1016/s0028-3908(98)00124-5.
The objectives of this study, conducted on neonatal rat spinal cord and dorsal roots in vitro, were to characterise the actions of a range of willardiine analogues on GluR5-containing kainate receptors present in dorsal roots, to determine whether GluR5-containing receptors are also present on motoneurones, and to differentiate responses mediated by kainate receptors from those mediated by AMPA receptors on motoneurones. (S)-5-Trifluoromethyl-willardiine, (S)-5-iodowillardiine, (S)-5-iodo-6-azawillardiine and ATPA were found to be potent agonists of kainate receptors on dorsal roots (EC50 values 0.108 +/- 0.002, 0.127 +/- 0.010, 0.685 +/- 0.141 and 1.3 +/- 0.3 microM, respectively) being more potent but of lower efficacy than kainate (EC50 value 14.8 +/- 1.8 microM). (S)-5-Iodo-6-azawillardiine blocked kainate-induced depolarisations of the dorsal root, probably via its desensitising action. Kainate-induced responses of dorsal roots were weakly antagonised by (RS)-3,5-dicarboxyphenylglycine (DCPG) (apparent KD 1.5 +/- 0.4 mM). Kainate receptors containing GluR5 subunits do not appear to be present on motoneurones since (RS)-3,5-DCPG (1 mM) potentiated rather than antagonised kainate-induced depolarisations of motoneurones. Although (S)-5-iodowillardiine (a potent and selective agonist at GluR5-containing kainate receptors) depolarised motoneurones (EC50 value 5.8 +/- 0.6 microM), such depolarisations were antagonised by both (RS)-3,4- and (RS)-3,5-DCPG, which are selective AMPA receptor antagonists at motoneurones, showing a KD value of 73 microM (Schild slope, 0.96 +/- 0.09) and an apparent KD value of 123 +/- 38 microM, respectively. This accords with the previously reported activity of willardiine analogues at AMPA receptors. Since neither (RS)-3,4- nor (RS)-3,5-DCPG antagonised kainate-induced motoneuronal depolarisations but cyclothiazide enhanced and GYK153655 blocked these responses it is possible that a component of the kainate response may be mediated by a population of DCPG-insensitive AMPA receptors on motoneurones. However, it is also possible that a population of kainate receptors other than those containing GluR5 subunits, are responsible for these effects. The new compounds introduced in this study are likely to be useful tools for studying the physiological role of kainate receptors in CNS function.
本研究在新生大鼠脊髓和背根的体外实验中开展，其目的是表征一系列威拉地丁类似物对背根中含GluR5的海人藻酸受体的作用，确定含GluR5的受体是否也存在于运动神经元上，并区分海人藻酸受体介导的反应与运动神经元上AMPA受体介导的反应。发现（S）-5-三氟甲基-威拉地丁、（S）-5-碘威拉地丁、（S）-5-碘-6-氮杂威拉地丁和ATPA是背根上海人藻酸受体的强效激动剂（EC50值分别为0.108±0.002、0.127±0.010、0.685±0.141和1.3±0.3 microM），比海人藻酸更有效但效能更低（EC50值为14.8±1.8 microM）。（S）-5-碘-6-氮杂威拉地丁可能通过其脱敏作用阻断海人藻酸诱导的背根去极化。海人藻酸诱导的背根反应被（RS）-3,5-二羧基苯基甘氨酸（DCPG）微弱拮抗（表观KD为1.5±0.4 mM）。含GluR5亚基的海人藻酸受体似乎不存在于运动神经元上，因为（RS）-3,5-DCPG（1 mM）增强而非拮抗海人藻酸诱导的运动神经元去极化。尽管（S）-5-碘威拉地丁（含GluR5的海人藻酸受体的强效选择性激动剂）使运动神经元去极化（EC50值为5.8±0.6 microM），但这种去极化被（RS）-3,4-和（RS）-3,5-DCPG拮抗，它们是运动神经元上的选择性AMPA受体拮抗剂，KD值分别为73 microM（希尔斜率，0.96±0.09）和表观KD值为123±38 microM。这与先前报道的威拉地丁类似物在AMPA受体上的活性一致。由于（RS）-3,4-和（RS）-3,5-DCPG均未拮抗海人藻酸诱导的运动神经元去极化，但环噻嗪增强且GYK153655阻断了这些反应，因此海人藻酸反应的一部分可能由运动神经元上一群对DCPG不敏感的AMPA受体介导。然而，也有可能是除含GluR5亚基的受体之外的一群海人藻酸受体负责这些效应。本研究中引入的新化合物可能是研究海人藻酸受体在中枢神经系统功能中的生理作用的有用工具。
