Autoradiographic localization of serum retinol-binding protein receptors on the pigment epithelium of dystrophic rat retinas.

The density and distribution of the retinal pigment epithelium membrane receptor for serum retinol-binding protein (RBP) was compared in young rats (28 days postnatal) and adult rats (7.5 months postnatal) afflicted with retinal dystrophy. Following an intravascular injection of 125I-labeled RBP (125I-RBP) complexed with prealbumin, the binding of 125I-RBP was analyzed by quantitative autoradiographic methods. As the course of the disease progressed, the pigment epithelium of the dystrophic retina underwent regional modification. Some areas remained unchanged, whereas others were grossly altered by vascular infiltration or by attenuation due to reduction in cell number. The basal infoldings of the pigment epithelium in young and adult rats exhibited nearly identical binding densities for 125I-RBP when unmodified cells were compared. In areas of severe disruption, the blood-retinal barrier was compromised, and the labeled protein diffused readily into the the neural retina. The results imply that the RBP receptors persist on the surface of unmodified pigment epithelial cells in adult dystrophic retinas in spite of the decrease in demand for retinol that accompanies the loss of photoreceptors.