title: Fluorescent imaging reports an extracellular alkalinization induced by glutamatergic activation of isolated retinal horizontal cells.
abstract: Extracellular acidification induced by retinal horizontal cells has been hypothesized to underlie lateral feedback inhibition onto vertebrate photoreceptors. To test this hypothesis, the H(+)-sensitive fluorophore 5-hexadecanoylaminofluorescein (HAF) was used to measure changes in H(+) from horizontal cells isolated from the retina of the catfish. HAF staining conditions were modified to minimize intracellular accumulation of HAF and maximize membrane-associated staining, and ratiometric fluorescent imaging of cells displaying primarily membrane-associated HAF fluorescence was conducted. Challenge of such HAF-labeled cells with glutamate or the ionotropic glutamate receptor agonist kainate produced an increase in the fluorescence ratio, consistent with an alkalinization response of +0.12 pH units and +0.23 pH units, respectively. This alkalinization was blocked by the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), the L-type calcium channel blocker nifedipine, and lanthanum. The alkalinization reported by HAF was consistent with extracellular alkalinizations detected in previous studies using self-referencing H(+)-selective microelectrodes. The spatial distribution of the kainate-induced changes in extracellular H(+) was also examined. An overall global alkalinization around the cell was observed, with no obvious signs of discrete centers of acidification. Taken together, these data argue against the hypothesis that glutamatergic-induced efflux of protons from horizontal cells mediates lateral feedback inhibition in the outer retina.
authors: Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois;
authors: Jason
authors: J
authors: Jacoby
authors: Matthew A
authors: MA
authors: Kreitzer
authors: Simon
authors: S
authors: Alford
authors: Robert Paul
authors: RP
authors: Malchow
mesh_terms: D000818:Animals; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D045604:Extracellular Fluid / Q000737:chemistry*; D005452:Fluoresceins; D005456:Fluorescent Dyes; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007059:Ictaluridae; D007608:Kainic Acid / Q000494:pharmacology; D061848:Optical Imaging; D017470:Receptors, Glutamate / Q000378:metabolism*; D051248:Retinal Horizontal Cells / Q000187:drug effects / Q000378:metabolism*
chemical_list: D018690:Excitatory Amino Acid Agonists; D005452:Fluoresceins; D005456:Fluorescent Dyes; D017470:Receptors, Glutamate; D018698:Glutamic Acid; C058719:(hexadecanoyl)aminofluorescein; D007608:Kainic Acid
keywords: feedback; horizontal cell; retina