Melatonin potentiates glycine currents through a PLC/PKC signalling pathway in rat retinal ganglion cells
Melatonin potentiates glycine currents through a PLC/PKC signalling pathway in rat retinal ganglion cells
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DOI：
10.1113/jphysiol.2010.187641
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发表时间：
2010-07
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影响因子：
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通讯作者：
Wen-jie Zhao;Min Zhang;Y. Miao;Xiong-Li Yang;Zhongfeng Wang
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作者：
Wen-jie Zhao;Min Zhang;Y. Miao;Xiong-Li Yang;Zhongfeng Wang
在脊椎动物视网膜中，褪黑激素调节各种生理功能。在这项工作中，我们研究了褪黑激素诱导的大鼠视网膜神经节细胞（RGC）甘氨酸电流增强的机制。免疫荧光双标记显示，大鼠RGCs仅对褪黑素MT 2受体呈免疫反应性。褪黑素增强RGCs的甘氨酸电流，这被MT 2受体拮抗剂4-P-PDOT逆转。褪黑激素的作用被GDP-β-S的细胞内透析阻断。与百日咳毒素预孵育或应用磷脂酰胆碱（PC）特异性磷脂酶C（PLC）抑制剂D 609，但不是磷脂酰肌醇（PI）-PLC抑制剂U 73122，阻断褪黑激素的作用。蛋白激酶C（PKC）激活剂PMA增强甘氨酸电流，在PMA存在下，褪黑激素未能引起电流的进一步增强，而PKC抑制剂双吲哚马来酰亚胺IV的应用消除了褪黑激素诱导的增强。BAPTA螯合[Ca ~（2+）]i后，褪黑素的作用持续存在，且褪黑素不引起[Ca ~（2+）]i的增加。cAMP‐PKA和cGMP‐PKG信号通路似乎均不参与，因为8‐Br‐cAMP或8‐Br‐cGMP未能引起甘氨酸电流的增强，PKA抑制剂H‐89和PKG抑制剂KT 5823均未阻断褪黑激素诱导的增强。因此，在Gi/o-偶联MT 2受体激活后，一种独特的PC-PLC/PKC信号通路最有可能是褪黑激素诱导的大鼠RGC甘氨酸电流增强的原因。此外，在大鼠视网膜切片中，褪黑激素增强了RGC中光诱发甘氨酸受体介导的抑制性突触后电流。这些结果表明，褪黑激素，在夜间处于较高的水平，可能有助于动物检测阳性或阴性对比度在夜间视觉调节抑制信号主要是由甘氨酸能无长突细胞介导的内层视网膜。
In vertebrate retina, melatonin regulates various physiological functions. In this work we investigated the mechanisms underlying melatonin‐induced potentiation of glycine currents in rat retinal ganglion cells (RGCs). Immunofluorescence double labelling showed that rat RGCs were solely immunoreactive to melatonin MT2 receptors. Melatonin potentiated glycine currents of RGCs, which was reversed by the MT2 receptor antagonist 4‐P‐PDOT. The melatonin effect was blocked by intracellular dialysis of GDP‐β‐S. Either preincubation with pertussis toxin or application of the phosphatidylcholine (PC)‐specific phospholipase C (PLC) inhibitor D609, but not the phosphatidylinositol (PI)‐PLC inhibitor U73122, blocked the melatonin effect. The protein kinase C (PKC) activator PMA potentiated the glycine currents and in the presence of PMA melatonin failed to cause further potentiation of the currents, whereas application of the PKC inhibitor bisindolylmaleimide IV abolished the melatonin‐induced potentiation. The melatonin effect persisted when [Ca2+]i was chelated by BAPTA, and melatonin induced no increase in [Ca2+]i. Neither cAMP‐PKA nor cGMP‐PKG signalling pathways seemed to be involved because 8‐Br‐cAMP or 8‐Br‐cGMP failed to cause potentiation of the glycine currents and both the PKA inhibitor H‐89 and the PKG inhibitor KT5823 did not block the melatonin‐induced potentiation. In consequence, a distinct PC‐PLC/PKC signalling pathway, following the activation of Gi/o‐coupled MT2 receptors, is most likely responsible for the melatonin‐induced potentiation of glycine currents of rat RGCs. Furthermore, in rat retinal slices melatonin potentiated light‐evoked glycine receptor‐mediated inhibitory postsynaptic currents in RGCs. These results suggest that melatonin, being at higher levels at night, may help animals to detect positive or negative contrast in night vision by modulating inhibitory signals largely mediated by glycinergic amacrine cells in the inner retina.