Table 2.
OS cholesterol content in human retina
| Total cholesterol, pmol | |||
|---|---|---|---|
| Gender | Age | Macula* | Periphery |
| M | 50 | 290 (1.26) | 230 |
| M | 59 | 229 (1.39) | 164 |
| M | 63 | 250 (1.19) | 210 |
| M** | 64 | 100 (0.70) | 142 |
| M | 63 | 67 (2.09) | 32 |
| M | 78 | 213 (1.25) | 171 |
| M | 85 | 232 (1.74) | 133 |
| M | 87 | 100 (0.32) | 310 |
| F | 57 | 60 (1.87) | 32 |
| F | 88 | 83 (1.93) | 43 |
Quantified by isotope-dilution gas-chromatography mass spectrometry as described (Mast et al., 2011) using deuterated cholesterol as internal standard. OS were obtained by laser-capture microdissection using 700 laser shots. Combined efforts of Saida Omarova, Casey D. Charvet, and Natalia Mast in the laboratory of IAP. Retinal sections were provided by CAC.
Number in parentheses represents fold difference relative to periphery
Material from 600 laser shots
Ten eyes with unremarkable maculas from donors 50-88 yr of age were used. Macular and peripheral samples of each eye were analyzed to permit within-eye comparison, using published values for rod and cone densities in these regions (Curcio et al., 1993; Curcio et al., 1990). We first computed the percentage of total photoreceptors in macula and periphery that were cones, where the macula was defined as a 6 mm diameter area centered on the fovea and periphery was centered at 13 mm temporal. In young adult macula, 9.3% of photoreceptors are cones, in older adult macula, 13.25% of photoreceptors are cones, and in peripheral retina of both ages. For periphery, the corresponding numbers are 3.7% and 3.1%. By assuming that laser shots captured rods and cones in proportion to their spatial densities, rod OS were dominated by disks containing 10% UC, and cone OS were dominated by plasma membrane containing 30% UC, we predict a macula/periphery (M/P) ratio for OS layer UC content in these assays of 1.09-1.18, depending on the age of the eye. In 8/10 eyes, the M/P ratio of total cholesterol was 1.19-2.19, thus exceeding this prediction and suggesting that cone OS are indeed enriched in UC relative to rods. There are limitations to this analysis. Cone OS are shorter than rod OS, thus effectively lowering the proportion of cone in the sample. More information about the membrane density of cone and rod OS (mm2/mm3) would strengthen this analysis. This question may also be answerable by comparing OS layer UC content in retinas from species that are more cone-dominated than human (e.g., pig, tree shrew, sand rat, NRL-knockout mouse).