Lateral diffusion of visual pigments in toad (Bufo marinus) rods and in catfish (Ictalurus punctatus) cones.

1. The lateral diffusion coefficient, D, was determined for visual pigments in red rods, green rods and red-sensitive cones with a photon-counting microspectrophotometer. 2. A novel protocol that involved the placement on a photoreceptor of a single micromeasuring/bleaching beam permitted the determination of D of the pigment. 3. Demonstration that D for red rods compared very well with values obtained by other workers using other means validated the protocol. 4. Applied to green rods, the protocol gave a value of D that was about 80% greater than that for red rods. 5. D for cone pigment was found to be slightly less than that of red rod pigment. 6. The dichroic ratio of cones and the average orientation of the chromophore in the cone lamellae were 1.71 and 28.4 deg, respectively. 7. The photosensitivity at lambda max of the red-sensitive cones was found to be about 16% less than that of red rods.