Fig. 10

Schematics of H⁺ negative feedback onto BCs via H⁺ concentration change at synaptic clefts of cone terminals induced by HC polarization. A H⁺ negative feedback onto OFF- and ON-type BCs via the series of effects of depolarization or hyperpolarization of HCs. The depolarization or hyperpolarization of HCs is induced either by OFF or ON of light illumination, respectively. ↑ denotes an activation or increase, whereas ↓ denotes an inactivation or decrease. In the presence of HEPES, synaptic cleft pH changes will be suppressed and bring about a change to the opposite direction to the control effect of HC polarization. These effects of HEPES imply the suppression of negative feedback ordinarily present in the control condition. B A schematic drawing of H⁺ negative feedback onto BCs via the concentration increase of H⁺ released from depolarized HCs into the synaptic cleft of cone terminals, illustrating OFF case in A. H⁺ release is due to V-ATPase (a proton pump located on plasma membrane shown by blue circles in an expanded figure) on depolarized HCs, resulting in suppression of glutamate release from cones. V-ATPase is also localized at the membrane of synaptic vesicles at the cone terminals