Signal Transduction
Guanylate cyclase–activating protein 2 contributes to phototransduction and light adaptation in mouse cone photoreceptors
Light adaptation of photoreceptor cells is mediated by Ca2+-dependent mechanisms. In darkness, Ca2+ influx through cGMP-gated channels into the outer segment of photoreceptors is balanced by Ca2+ extrusion via Na+/Ca2+, K+ exchangers (NCKXs). Light activates a G protein signaling cascade, which closes cGMP-gated channels and decreases Ca2+ levels in photoreceptor outer segment because of continuing Ca2+ extrusion by NCKXs. Guanylate cyclase–activating proteins (GCAPs) then up-regulate cGMP synthesis by activating retinal membrane guanylate cyclases (RetGCs) in low Ca2+.Regulation of Mammalian Cone Phototransduction by Recoverin and Rhodopsin Kinase
Background: Calcium-mediated feedback to phototransduction is critical for modulating cone responses under different lighting conditions.Results: The calcium-binding protein recoverin potentiates dim light sensitivity, whereas increasing expression of its target, GRK1, delays response shutoff in cones.Conclusion: Recoverin and GRK1 levels modulate cone phototransduction.Significance: Cone pigment inactivation regulates cone responses in dim light but not in bright light.
