Selective Zinc Labeling of Short Wavelength Cone Outer Segments

Abstract

Abstract: : Purpose: Zinc has been postulated to play a role in both normal and degenerative processes in the retina. Often these processes require zinc, which is tightly bound to enzymes. However, new evidences indicate that mobilizable zinc might also play a pivotal role . The purpose of this study was to identify the location of mobilizable zinc in the photoreceptor layer of retinae. Methods: Following deep anesthesia and decapitation, dark–adapted retinae were immediately dissected from rat, goldfish and chicken eyes and flat mounted with the photoreceptor up. The retinae were immediately labeled with the zinc–specific fluorescent chelator Zinpyr1. Readily releasable zinc was visualized using a fluorescent or confocal microscope . Results: Only a subset of photoreceptors were labeled by Zinpyr1 in rat retinae (>0.5 %). This labelling was localized to the outer segments of photoreceptors and appeared to label only a subset of the cones. The cone localization of this labeling was confirmed by using goldfish retinae where the cones are readily distinguishable from rods morphologically. To identify the subtype of zinc postive cones we labeled chicken retinae where the characteristic oil droplets within the cones, identifies their sub–type. Here zinc appeared to be localized to the short wavelength cone outer segments. Conclusions: We found that readily releasable zinc is localized to the outer segments of short wavelength cones. Therefore, zinc appears to play a selective role in visual processing of short wavelength light.

Keywords: photoreceptors • signal transduction • microscopy: light/fluorescence/immunohistochemistry