Photomechanical responses of visual receptors in the retina of the bullfrog (Rana catesbeiana).

All photoreceptor types in the bullfrog (Rana catesbeiana) retina exhibit changes of position within the receptor layer, depending upon the state of retinal adaptation, and the season in which the displacement was measured. The most light-adapted position of each photoreceptor type following monochromatic adaptation was not related specifically to the lambda-max of its own photopigment. In general, however, the response profiles were similar for photoreceptors having the same lambda-max. The red rod, accessory member of the double cone, green rod and the miniature cone showed similar response profiles, while the single cone and the principal member of the double cone showed similar patterns of movement as a function of adapting wavelength. The response profiles for the short and middle lambda-max photoreceptors obtained in summer months appeared similar to the action spectrum of the retinal pigment epithelium (RPE) as previously described by Liebman and co-workers. Seasonal differences were also found. The observed photomechanical response profiles may be determined by complex interactions between adjacent photoreceptors, as well.