| IntroductionZinc is an important trace element in human body. Zinc ion is an important component of a variety of enzymes and proteins. In the central nervous system, zinc content is extremely rich. Numerous studies have shown that free zinc ions, which function as neuromodulator, coexist with the neurotransmitters such as glutamate in synaptic vesicles of axonal terminals. Zinc can release into the synaptic cleft together with neurotransmitters, and can regulate NMDA, AMPA, glycine and GABA receptors.As one part of the central nervous system, retina also contains a certain concentration of zinc ions. Zinc ions may have an important role of regulating the relevant functional retina. Recent studies have shown that zinc transporters --may play a key role in the maintenance of intracellular zinc homeostasis. Seven members of zinc transporter family named ZNT1-7 have already been cloned, and their functions are well understood. It has been reported that ZNT3 is highly expressed in the retina. However, the localization of free zinc ions and other zinc transporters in the mouse retina have not been reported in detail. Therefore, in the present study, the autometallography, immunohistochemistry and Western Blot have been used to identify the localization and expression of free zinc ions and six members of ZNTs family, to further explore the function of zinc ions and zinc transporters in the visual system.Materials and MethodsForty adult male CD-1 mice (40-50g body weight) were housed in cages, and were feed with conventional diet and regular tap water. Autometallography, immunohistochemistry and Western Blot were used to analyze the localization and expression of free zinc ions and ZNT1, ZNT3, ZNT4, ZNT5, ZNT6, ZNT7 in the mouse retina. ResultsFree zinc ions and zinc transporters (ZNT1, ZNT3, ZNT4, ZNT5, ZNT6, ZNT7) were widely located in the mouse retinal layers. Free zinc ions were mainly distributed in the pigment epithelial cell layer, the photoreceptor inner segment, the outer nuclear layer, the outer plexiform layer, the inner nuclear layer, the inner plexiform layer and the ganglion cell layer. While zinc transporters were distributed in the different layers of the retina. ZNT1 and ZNT6 were distributed relatively similar; there was a strong positive reaction within the outer plexiform layer and the inner plexiform layer processes. Positive reaction of medium degree was in the nerve fiber layer, the ganglion cell layer and the layer of pigment epithelial cells. In the pigment epithelial cell layer, the inner segment and outer segment of the photoreceptor, ZNT6 immunoreactivity was stronger than that of ZNT1. However both ZNT1 and ZNT6 immuonoreactivities were not obvious in the inner nuclear layer and the outer layer of nuclear. ZNT3 positive reactions were diffusely distributed in the retina. Strong reactions of ZNT3 were found in the photoreceptor outer segment, the pigment epithelial cell layer, the outer plexiform layer and the inner plexiform layer processes. The immunoreactions of ZNT4 and ZNT7 existed in the ganglion cell layer and the pigment epithelial cell layer, while the outer plexiform layer and the inner plexiform layer processes showed a medium-level positive reaction. Strong positive reactions of ZNT5 were found in the photoreceptor outer segment, the ganglion cell layer, the inner nuclear layer, the photoreceptor inner segment and the pigment epithelial cell layer. ZNT5 positive reactions were also found in the outer plexiform layer and the inner plexiform layer of the processes.ConclusionMouse retina contains high amount of free zinc ions and zinc transporters ZNT1, ZNT3, ZNT4, ZNT5, ZNT6 and ZNT7. The results suggest that zinc might play some important roles in the visual message transduction and formation in the mouse retina. Consistent distribution between zinc ions and six zinc transporters suggests that ZNTs probably play important roles in the process of zinc metabolism in the mouse retina. |
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