Accumulation of Immunoreactive Opsin on Plasma Membranes in Degenerating Rod Cells of rd/rd Mutant Mice

Immunoreactive opsin was detectable in the apical portion of normally developing photoreceptor cells on postnatal day 3 by the indirect enzyme-labeled antibody method. Immunoreactivity increased and had ex-tended from the central retina to the periphery by the advanced stages of development. In the rd mutant retinas, accumulated opsin was present in the apical portion and in the outer nuclear layer on postnatal day 8. Immuno-reactive opsin mainly was present in the outer nuclear layer by day 14, even being detectable on day 28. No immunoreactivity was present in the remaining cones. Electron microscopic immunocytochemistry confirmed the association of immunoreactive opsin with the persistent rod cell plasma membrane. Mole-cular weight of immunoreactive opsin in 14-day-old rd mutant mouse retina, as estimated by gel filtration chromatography, was large and did not seem to be degraded. These findings indicate that accumulated rhodopsin continues to function in the plasma membrane because an electroretinogram could be made after day 14 for the rd mutant mouse retina.