April 2011
Volume 52, Issue 14
ARVO Annual Meeting Abstract  |   April 2011
Voltage-gated Calcium Channels in Horizontal Cells Mediate Inhibitory Feedback to Photoreceptors
Author Affiliations & Notes
  • Xue Liu
    Neurobiology, UCLA, Los Angeles, California
  • Arlene A. Hirano
    Neurobiology, UCLA, Los Angeles, California
  • Steven Barnes
    Neurobiology, UCLA, Los Angeles, California
    Physiology & Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada
  • Nicholas C. Brecha
    Neurobiology, UCLA, Los Angeles, California
    Veterans Administration, VAGLAHS, Los Angeles, California
  • Footnotes
    Commercial Relationships  Xue Liu, None; Arlene A. Hirano, None; Steven Barnes, None; Nicholas C. Brecha, None
  • Footnotes
    Support  NIH Grant EY 15573; VA Career Scientist Award (NB)
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 2570. doi:
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      Xue Liu, Arlene A. Hirano, Steven Barnes, Nicholas C. Brecha; Voltage-gated Calcium Channels in Horizontal Cells Mediate Inhibitory Feedback to Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2570.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : Horizontal cells (HCs) send inhibitory feedback to photoreceptors (PRs) but the mechanisms underlying this inhibition are not fully understood. Immunohistochemical (IHC) studies show that the proteins responsible for Ca-dependent vesicular fusion are present in HCs. The goal of this study is to determine the contribution of voltage-gated calcium channels (VGCCs) in HCs to feedback.

Methods: : Rat retinal slices loaded with Fluo-4 were imaged on a Zeiss Pascal confocal microscope. Brief superfusion with 30 mM K+ activated PR L-type Ca channels. 50 µM kainate (KA) and 50 µM NBQX were used to alter the feedback signal from HCs. 1.5 µM ω-conotoxin GVIA (CTX) and 400 nM ω-agatoxin IVA (ATX) were used to block N- and P/Q-type Ca channels, respectively. 20 µM dopamine D1 receptor (D1R) agonist SKF-38393 and 20 µM D2 receptor (D2R) antagonist spiperone were used to modulate dopamine pathways. IHC was used to study the localization of Ca channel subunits.

Results: : IHC analysis showed that L-, N- and P/Q-type Ca channels are present in HCs. N-type channels in particular were found to be localized to the tips of the HC processes. Consistent with previous reports, KA inhibited high K+-evoked Ca2+ signals in PRs by ~36%, whereas NBQX enhanced Ca2+ signals by ~27%. When the N-type Ca channel blocker CTX was applied, high K+-evoked Ca2+ signals were potentiated by ~28%. The P/Q-type channel blocker ATX also enhanced Ca2+ signals by ~40%. HC L-type Ca channels cannot be tested. Since high K+-evoked dopamine release might modulate Ca channels in PRs directly via D2Rs on PRs and indirectly via D1Rs on HCs, we tested these pathways. The D1R agonist SKF-38393 and the D2R antagonist spiperone were applied and had no modulatory effect on PR Ca2+ signals.

Conclusions: : These results show that block of N- and P/Q-type Ca channels in HCs diminishes feedback to PRs. This suggests that signaling from HCs to PRs is at least in part dependent on VGCCs, consistent with Ca-dependent vesicular release from HCs mediating inhibitory feedback.

Keywords: horizontal cells • calcium • photoreceptors 

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