Abstract
In most vertebrate retinas, there are two types of photoreceptor cells, rods and cones, which are responsible for twilight and daylight (color) vision, respectively. We have investigated molecular properties of rod and cone visual pigments and found the differences in kinetics of protein conformational changes between these pigments. We have also investigated the spectral tuning mechanisms of cone pigments and found the ways to manipulate the absorption spectra of cone pigments without other kinetic properties typical to cone pigments. Recent progress in gene-targeting technology in mice allows us to examine these molecular properties in vivo and to correlate them with physiological responses. Thus, we have replaced rod and cone pigments in respective photoreceptor cells, and examined the effect of replacements from the kinetic and spectral standpoints. To investigate the relationship between pigment properties and photoreceptor responses, we replaced wild-type rhodopsin with the mutant rhodopsin or cone pigments in rod cells and measured their responses by scotopic ERG and single-cell suction pipette techniques. The results showed that the differences in decay times of intermediate states correlated with the recovery of the dark current after moderate photobleaching of the pigments. We also replaced the green sensitive-cone pigment by red-shifted mutant pigment in cone cells. By photopic ERG and slice-patch recording of ganglion cells, the photoresponses of wild-type and mutant cone cells were integrated in some type of the ganglion cells. [Jpn J Physiol 55 Suppl:S48 (2005)]
