Distribution of carbonic anhydrase among human photoreceptors.
The distribution of carbonic anhydrase (CA) among human photoreceptors has been a topic of dispute. In our experiments, by modifying an established enzyme histochemical technique, reproducible staining was observed. Of the cones in the peripheral retina, 91% were positive for CA. The CA-negative (CA-) cones were absent within approximately 8 arc min of the foveal center and their density peaked at 2 arc deg. No CA activity was found in the rods. Morphologic differences were noted between the CA-positive (CA+) and CA- cones. Compared to the CA+ cones, the CA- cones had longer and more nearly columnar inner segments, more nearly spherical nuclei, and more generous amounts of perikaryal cytoplasm. In the peripheral retina, the distance between CA+ to CA+ nearest neighbors were larger compared to CA- to CA+ nearest neighbors (P less than 0.0001). The frequency distribution and morphology of the CA- cones suggest that they are the blue-sensitive cones. As such, this study demonstrates a biochemical similarity between blue cones and rods that may provide insight into the function and phylogeny of the blue cones.
Nork
T M
TM
Department of Ophthalmology, West Virginia University Health Sciences Center, Morgantown 26506.
McCormick
S A
SA
Chao
G M
GM
Odom
J V
JV
D000328:Adult; D000704:Analysis of Variance; D002256:Carbonic Anhydrases / Q000378:metabolism*; D005584:Fovea Centralis / Q000201:enzymology; D006651:Histocytochemistry; D006801:Humans; D010786:Photoreceptor Cells / Q000201:enzymology*; D013048:Specimen Handling
D002256:Carbonic Anhydrases