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Melatonin potentiates glycine currents through a PLC/PKC signalling pathway in rat retinal ganglion cells
Author(s) -
Zhao WenJie,
Zhang Min,
Miao Yanying,
Yang XiongLi,
Wang Zhongfeng
Publication year - 2010
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2010.187641
Subject(s) - melatonin , long term potentiation , protein kinase c , medicine , melatonin receptor , endocrinology , pertussis toxin , phospholipase c , biology , receptor , chemistry , microbiology and biotechnology , signal transduction , g protein
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 MT 2 receptors. Melatonin potentiated glycine currents of RGCs, which was reversed by the MT 2 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 [Ca 2+ ] i was chelated by BAPTA, and melatonin induced no increase in [Ca 2+ ] 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 G i/o ‐coupled MT 2 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.