Lectin receptors of rods and cones. Visualization by fluorescent label

The binding of eight fluorescence-labeled lectins to visual cells was investigated. Concanavalin A (Con A) (specific for oligosaccharides containing mannose) bound evenly to the surfaces of rod outer segments (ROSs) from frog, cattle, goldfish, and turtle (Pseudemys). In frog, binding was observed on the inner segment, with intensifications at the inner/outer segment junction and in the region of the nucleus. No binding occurred on the surfaces of ROS discs. In 0.1% Triton X-100, rods formed convoluted tubular structures that bound Con A to their surfaces. Isolated cone outer segments (COSs) showed uniform fluorescence as compared with the inner segments, which displayed only surface labeling. Only lectins with an affinity for fucose (UeA, LTA) failed to bind to the ROSs and COS. Lectins with an affinity for oligosaccharides containing galactose (RCA-120, RCA-60, and PNA) bound hardly at all to the rod inner segments. Both WGA (N-acetyl glucosamine) and SBA (N-acetyl galactosamine and galactose) bound indiscriminately to all ROSs, whereas PNA bound preferentially to the accessory cones.