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Zinc Transport in Vertebrate Retina

¹ The Graduate Center, CUNY, New York, New York
² Hunter College, CUNY, New York, New York

Zinc transporter-protein-3 (ZnT-3) has six transmembrane domains with a histidine-rich cytoplasmic loop responsible for mediating zinc transport. Studies of the central nervous system have localized ZnT-3 primarily to glutamatergic vesicles containing up to 300 µM zinc. We initially examined the distribution of the ZnT-3 protein in the light-adapted mouse retina using immunohistochemical techniques. The ZnT-3 protein was most concentrated in the region of the outer limiting membrane and photoreceptor inner segments, a mitochondrion-rich region where disk formation occurs. Strong labeling was also observed in the inner nuclear and ganglion cell layers. Weaker ZnT-3 reaction bands were present in the inner plexiform layer. In contrast, the outer nuclear layer and photoreceptor outer segments remained clear of ZnT-3 immunoreactivity. In general, ZnT-3 appeared to be localized in regions that have previously been found reactive for ionic zinc in light-adapted murine retinas.

In the present study, to verify cellular ZnT-3 localization, we isolated mouse retinal neurons and antibody-labeled for ZnT-3. With DAB labeling, Müller cell apical villi, soma, and endfeet exhibited ZnT-3 reactivity. Using FITC label and confocal analysis, ZnT-3 protein appeared to be localized throughout the Müller cell.

The dense labeling for ZnT-3 in the photoreceptor inner segment region has been puzzling since this is not a likely site for synaptic vesicles. It is, however, a location rich with the apical villi of Müller cells which may well account for this labeling. In fact, the Müller cell soma and endfeet are also present in other retinal layers reactive for ZnT-3, where they may also contribute to labeling observed. Based on these findings, it seems possible that Müller cells utilize ZnT-3 to regulate retinal zinc homeostasis.

Support: Fight for Sight, PSC/CUNY Grant 66257-0035, and NCRR/NIH RCMI Award RR-03037 (RLC).

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Redenti, S. Articles by Chappell, R. L. Search for Related Content PubMed Articles by Redenti, S. Articles by Chappell, R. L.