Phototransduction in mouse rods and cones

Abstract

Phototransduction is the process by which light triggers an electrical signal in a photoreceptor cell. Image-forming vision in vertebrates is mediated by two types of photoreceptors: the rods and the cones. In this review, we provide a summary of the success in which the mouse has served as a vertebrate model for studying rod phototransduction, with respect to both the activation and termination steps. Cones are still not as well-understood as rods partly because it is difficult to work with mouse cones due to their scarcity and fragility. The situation may change, however.

Fig. 1

Form of the single-photon response from knockout mouse rods with deficient R* termination on fast (a) and slow (b) timescales. Flashes were delivered at t=0. Figure was kindly supplied by Dr. M. E. Burns

Fig. 2

Schematic on the termination G*-PDE*. Gα*-GTP binds to PDEγ and activates PDE. The deactivation of Gα*-GTP is accelerated by the GAP complex, R9AP-RGS9-1-Gβ5L, in which RGS9-1 facilitates the hydrolysis of the bound GTP to GDP, leading to the reformation of the inactive heterotrimeric Gα-GDP-Gβγ and inactive PDE. An asterisk denotes the active state. This step was found to be the rate-limiting step of rod recovery [56]

Fig. 3

Flash responses of mouse cone photoreceptors from different genotypes. a Comparison of the average response of S-cones to 361-nm flashes and M-cones to 510-nm flashes. b Comparison of the average flash responses to 361-nm flashes of wild-type S-cones, gnat1^−/− S-cones, Nrl^−/− cones, and rods recorded under the same “OS out” conditions. Each trace is scaled to unity at its peak. Data from Fig. 4e,f of [67]. Reproduced from The Journal of General Physiology, 2006, 127: 359–374. Copyright 2006 The Rockefeller University Press