External Proton Mediates the Feedback from Horizontal Cells to Cones in the Newt Retina

The center-surround organization of the receptive fields is one of the most important properties of retinal neurons. Cone photoreceptors show concentric receptive field; they are hyperpolarized by spot light and depolarized by annulus light. It is widely accepted that the negative feedback from horizontal cells (HCs) generates the surround response of cones. Although accumulating evidence suggests that γ-aminobutyric acid (GABA) mediates the feedback from HC to cones, there are still a number of reports criticizing the GABA hypothesis of HC-cone feedback. In the goldfish, Verweij et al. [1] have reported that the feedback was detectable in the presence of GABA antagonist, and the surround illumination shifted the activation voltage of the cone calcium current (ICa) to be more negative. In the present study, we reexamined the mechanism of feedback to find an answer to this controversy.