Abstract Extracellular H + has been hypothesized to mediate feedback inhibition from horizontal cells onto vertebrate photoreceptors. According to this hypothesis, depolarization of horizontal cells should induce extracellular acidification adjacent to the cell membrane. Experiments testing this hypothesis have produced conflicting results. Studies examining carp and goldfish horizontal cells loaded with the pH-sensitive dye 5-hexadecanoylaminofluorescein (HAF) reported an extracellular acidification on depolarization by glutamate or potassium. However, investigations using H + -selective microelectrodes report an extracellular alkalinization on depolarization of skate and catfish horizontal cells. These studies differed in the species and extracellular pH buffer used and the presence or absence of cobalt. We used both techniques to examine H + changes from isolated catfish horizontal cells under identical experimental conditions (1 mM HEPES, no cobalt). HAF fluorescence indicated an acidification response to high extracellular potassium or glutamate. However, a clear extracellular alkalinization was found using H + -selective microelectrodes under the same conditions. Confocal microscopy revealed that HAF was not localized exclusively to the extracellular surface, but rather was detected throughout the intracellular compartment. A high degree of colocalization between HAF and the mitochondrion-specific dye MitoTracker was observed. When HAF fluorescence was monitored from optical sections from the center of a cell, glutamate produced an intracellular acidification. These results are consistent with a model in which depolarization allows calcium influx, followed by activation of a Ca 2+ /H + plasma membrane ATPase. Our results suggest that HAF is reporting intracellular pH changes and that depolarization of horizontal cells induces an extracellular alkalinization, which may relieve H + -mediated inhibition of photoreceptor synaptic transmission. retina feedback lateral inhibition « Previous | Next Article » Table of Contents This Article Published online before print November 2011 , doi: 10.​1152/​jn.​00878.​2011 AJP - JN Physiol February 2012 vol. 107 no. 3 868-879 » Abstract Free Full Text Free to you Full Text (PDF) Free to you All Versions of this Article: jn.00878.2011v1 107/3/868 most recent Classifications Article Services Email this article to a friend Alert me when this article is cited Alert me if a correction is posted Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Download to citation manager Citing Articles Load citing article information Citing articles via Web of Science Google Scholar Articles by Jacoby, J. Articles by Malchow, R. P. PubMed PubMed citation Articles by Jacoby, J. Articles by Malchow, R. P. Related Content Load related web page information Current Issue February 2012, 107 (3) Alert me to new issues of AJP - JN Physiol About the Journal Information for Authors Submit a Manuscript Ethical Policies AuthorChoice PubMed Central Policy Reprints and Permissions Advertising Press Copyright © 2012 the American Physiological Society Print ISSN: 0022-3077 Online ISSN: 1522-1598 var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www."); document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E")); var pageTracker = _gat._getTracker("UA-2924550-1"); pageTracker._trackPageview();

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