Physiological Studies of the Interaction Between Opsin and Chromophore in Rod and Cone Visual Pigments

The visual pigment in vertebrate photoreceptors is a G protein-coupled receptor that consists of a protein, opsin, covalentlyattached to a chromophore, 11-
cis-
retinal. Activation of the visual pigment by light triggers a transduction cascade that produces experimentally measurableelectrical responses in photoreceptors. The interactions between opsin and chromophore can be investigated with electrophysiologialrecordings in intact amphibian and mouse rod and cone photoreceptor cells. Here we describe methods for substituting the nativechromophore with various chromophore analogs to investigate how specific parts of the chromophore affect the signaling propertiesof the visual pigment and the function of photoreceptors. We also describe methods for genetically substituting the nativerod opsin gene with cone opsins or with mutant rod opsins to investigate and compare their signaling properties. These methodsare useful not only for understanding the relation between the properties of visual pigments and the function of photoreceptorsbut also for understanding the mechanisms by which mutations in rod opsin produce night blindness and other visual disorders.