d-[ 3H]-galactose incorporation in the bovine retina: Specific uptake and transport of the radiolabel in cones

When bovine neural retinas are incubated in Krebs-Henseleit buffer with d-[ 3H]-galactose, autoradiography reveals that there is a rapid uptake of the tritium label into the inner segments of cones, but not of rods. Pulse-chase studies show that the label is first associated with the Golgi apparatus in the cones, then appears to travel around the nucleus and along the cone fibre (homologous to an axon) to the synaptic pedicle. The cone-specific label travels along the fibre at a rate of about 0·5–1·0 mm per day. Label is also found in endothelial cells and Müller cells, but does not persist in the Müller cells as long as in the cones. The striking difference between rod and cone labelling may reflect fundamental differences in the neurochemistry of these two photoreceptor cell types.