title: Depolarization of isolated horizontal cells of fish acidifies their immediate surrounding by activating V-ATPase.
abstract: In order to interpret the formation of receptive field surrounds in retinal neurons, a proton-mediated mechanism was proposed to mediate feedback from horizontal cells (HCs) to cone photoreceptors. To verify the idea that depolarized HCs release protons, we measured, by a fluorescence ratiometric technique, the pH of the immediate external surface (pHs) of HCs isolated from the carp or goldfish retina. When HCs stained by 5-hexadecanoylaminofluorescein, a pH-sensitive lipophilicdye, were depolarized by bath-application of kainate or high-K+ medium, pHs was lowered. The amount of pHs change was monotonically dependent on the degree of depolarization, as much as 0.21 +/- 0.05 pH units by 100 mV depolarization (induced by 100 mm K+). Acidification was suppressed by 400 nm bafilomycin A1, a specific inhibitor of the vacuolar type H+ pump (V-ATPase), suggesting that depolarization released protons from HCs via the voltage-sensitive H+ pump. Immunocytochemical analysis, using an anti-V-ATPase antibody, revealed the existence of V-ATPase in dissociated HCs. These results support the hypothesis that the feedback from HCs to cones could be proton mediated.
authors.affiliation: Department of Biological Sciences, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Jouhou
authors.forename: Kazunori
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Akinori
authors.initials: A
authors.lastname: Homma
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hara
authors.forename: Akimichi
authors.initials: A
authors.lastname: Kaneko
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yamada
mesh_terms: D000143:Acids / Q000378:metabolism*; D000818:Animals; D002347:Carps; D002450:Cell Communication / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D025461:Feedback, Physiological / Q000502:physiology; D006054:Goldfish; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007608:Kainic Acid / Q000494:pharmacology; D018942:Macrolides / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000502:physiology; D051248:Retinal Horizontal Cells / Q000166:cytology* / Q000502:physiology*; D013569:Synapses / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000143:Acids; D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D018942:Macrolides; C040929:bafilomycin A1; D025262:Vacuolar Proton-Translocating ATPases; D011188:Potassium; D007608:Kainic Acid