Investigation of luminal surface structures of rod photoreceptor outer segments by lectin cytochemistry combined with...

The luminal surface of the rod photoreceptor disk membrane was exposed by means of osmotic shock and labeled with ferritin- conjugated concanavalin A. The structural changes of the luminal surface were examined by a freeze-etching procedure with cryoprotectant (methanol). On replicas from freeze-etched membranes with concanavalin A labeling, 6- to 10-nm particles were codistributed with ferritin particles on the luminal surface of the disk membrane. By contrast, there were few ferritin particles or less numerous 6- to 10-nm particles on the corresponding surface without concanavalin A labeling. If 6- to 10-nm particles corresponded to the carbohydrate moiety of rhodopsin, concanavalin A binding might tend to preserve this carbohydrate moiety. These results suggest that the two-dimensional analysis of lectin-induced structural changes of the membrane surface glycoconjugates may become available by lectin cytochemistry combined with freeze-etching.