EXPOSURE OF ROD OUTER SEGMENTS TO SERUM IS NOT RESPONSIBLE FOR ABNORMAL DISK MEMBRANE MORPHOGENESIS IN A MODEL OF RETINAL-DETACHMENT

Purpose. The sclerad surface of the retina is exposed to serum protein s in several retinal pathologies that result in degeneration of photor eceptor outer segments. Abnormal disk membrane morphogenesis is observ ed in rod photoreceptors of detached Xenopus retinas when they are cul tured in serum-containing medium. Retinas that remain attached to the pigment epithelium layer produce normal disks. Experiments were conduc ted to determine whether abnormal disk morphogenesis in detached, cult ured retinas is due to the presence of serum in the microenvironment o f the rod outer segments. Methods. Detached retinas and retinas attach ed to the retinal pigment epithelium in eyecups were cultured in eithe r serum-containing or serum-free medium, and the morphology of the dis k lamellae formed in vitro retinas was evaluated. Using protein extrac tion and immunochemical methods, the presence of albumin in the microe nvironment of the outer segments was confirmed for retinas incubated i n serum-containing medium. Results. There were no obvious differences in the abnormal disk-like lamellae formed in detached retinas when the retinas were incubated either in serum-containing or in serum-free cu lture medium. Proteins extracted from detached retinas cultured in ser um-containing medium showed a prominent band at 63 kDa that co-localiz ed primarily with outer segment-enriched fractions. Immunolabeling sho wed that the band was serum albumin. Conclusions. Rod cells in detache d retinas formed abnormal disk-like lamellar membranes in either serum -containing or serum-free medium. This suggests that exposing outer se gments to serum albumin or other serum components is not responsible f or the abnormal in vitro disk membrane morphogenesis seen in detached retinas.