Depolarization of isolated horizontal cells of fish acidifies their immediate surrounding by activating V-ATPase

• Published in: The Journal of physiology 2007-12, Vol.585 (2), p.401-412
• Main Authors: Jouhou, Hiroshi, Yamamoto, Kazunori, Homma, Akinori, Hara, Masayuki, Kaneko, Akimichi, Yamada, Masahiro
• Format: Article
• Language: English
• Subjects: Acids - metabolism; Animals; Carps; Cell Communication - physiology; Enzyme Inhibitors - pharmacology; Excitatory Amino Acid Agonists - pharmacology; Extracellular Space - metabolism; Feedback, Physiological - physiology; Goldfish; Hydrogen-Ion Concentration; Immunohistochemistry; Kainic Acid - pharmacology; Macrolides - pharmacology; Membrane Potentials - drug effects; Membrane Potentials - physiology; Neuroscience; Potassium - pharmacology; Retinal Cone Photoreceptor Cells - cytology; Retinal Cone Photoreceptor Cells - physiology; Retinal Horizontal Cells - cytology; Retinal Horizontal Cells - physiology; Synapses - metabolism; Vacuolar Proton-Translocating ATPases - antagonists & inhibitors; Vacuolar Proton-Translocating ATPases - metabolism
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2007.142646

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 (pH s ) of HCs isolated from the carp or goldfish retina. When HCs stained by 5-hexadecanoylaminofluorescein, a pH-sensitive lipophilic dye, were depolarized by bath-application of kainate or high-K + medium, pH s was lowered. The amount of pH s 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 m m K + ). Acidification was suppressed by 400 n m 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.