Abstract
Hirasawa and Kaneko (2003) proposed a pH-mediated feedback mechanism from horizontal cells (HCs) to cone photoreceptors to interpret the formation of receptive field surrounds in the retinal neurons. To verify the idea that the depolarized HCs release proton, we measured the pH of the external surface (pHo) of HCs isolated from the carp or goldfish retina by a fluorescence ratio imaging technique using a pH-sensitive lipophilic dye, 5-hexadecanoylaminofluorescein. When HCs were depolarized by kainate or high extracellular K+, pHo was shifted to acidic side. Electrophysiological and imaging experiments showed that bafilomycin A1,a specific inhibitor of vacuolar type H+-ATPase (V-ATPase), suppressed depolarization-induced shift of pHo.Localization of V-ATPase was examined by immunohistochemistry using an anti V-ATPase antibody. In isolated HCs immunoreactivity was observed on the cytoplasmic membrane. In retinal slice preparations, anti-V-ATPase immunoreactivity was found at the cone terminals and on the surface of GAD-positive external HCs.These results suggest that HC dendrites can be the active sites of proton extrusion supporting the proton hypothesis for the feedback from HCs to cone photoreceptors. [J Physiol Sci. 2007;57 Suppl:S149]
