Transduction steps which characterize retinal cone current responses to flash stimuli.
There are three prominent characteristics in current responses of retinal cones to flash stimuli when compared with those of rods. First, the time-to-peak of the photocurrent is two to four times faster than for the rod. Second, the photosensitivity of the cone is more than one order of magnitude lower than that of the rod. Third, current responses of cones resemble characteristic under-shoot in the recovery phase. At present, however, it is not known what kinds of mechanisms underlie these characteristics. In the present study, critical steps which characterize cone responses have been investigated by changing rate constants in the model for the signal transduction scheme of cone outer segments under the assumption that the scheme is basically the same as for rods. The computer simulations have shown that rate constants were divided into three categories: those which do not appreciably change photocurrent, those which change only photosensitivity, and those which change both sensitivity and speed. Furthermore, rate constants which characterize undershoot were identified. From these simulations it has been revealed that characteristics of the cone response could be reproduced by changing the rate constants. The critical ones are rate of rhodopsin deactivation, rate of GTP hydrolysis, and deactivation rate of activated phosphodiesterase. These results suggest possibilities that the signal transduction mechanisms in cones are basically the same as those for rods, while rate constants are different.
Ichikawa
K
K
Foundation Research Laboratory, Fuji Xerox Co. Ltd., Kanagawa, Japan.
D000818:Animals; D003198:Computer Simulation; D004594:Electrophysiology; D006801:Humans; D008959:Models, Neurological; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012374:Rod Cell Outer Segment / Q000502:physiology; D015398:Signal Transduction