April 2011
Volume 52, Issue 14
Free
ARVO Annual Meeting Abstract  |   April 2011
Canonical Trp Channels (Trpc1 and Trpc3) Regulate Neurotransmission And Visual Acuity In The Mouse Retina
Author Affiliations & Notes
  • David Krizaj
    Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, Utah
  • Lutz Birnbaumer
    NIH/NIEHS, Research Triangle Park, North Carolina
  • Peter Barabas
    Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, Utah
  • Footnotes
    Commercial Relationships  David Krizaj, None; Lutz Birnbaumer, None; Peter Barabas, None
  • Footnotes
    Support  NIH EY 13870, P30EY014800, Foundation Fighting Blindness, International Retina Research Foundation, Moran Tiger Award, RPB Institutional grant
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 4121. doi:
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      David Krizaj, Lutz Birnbaumer, Peter Barabas; Canonical Trp Channels (Trpc1 and Trpc3) Regulate Neurotransmission And Visual Acuity In The Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4121.

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Abstract 
 
Purpose:
 

To analyze light-evoked responses and visual behavior in mice lacking vertebrate homologs of the Drosophila TRP channel. TRP channels play a fundamental role in invertebrate photoreceptor signaling. Their canonical (TRPC) homologs have been implicated in ip-RGC phototransduction, however, expression and function of specific TRPC isoforms in vertebrate retinas is unknown.

 
Methods:
 

RT-PCR was used to analyze the expression of Trpc1 -7 genes in wild type, KO and Pde6brd1 mice. Mouse lines lacking Trpc1 (TRPC1-/-), Trpc3 (TRPC3-/-) and Trpc1/Trpc3 (TRPC1/3-/-) genes were tested for visual acuity and for light-evoked responses under photopic and scotopic conditions. Contrast sensitivity functions were obtained for optokinetic reflex (OKR) responses to moving sine-wave gratings using a virtual optomotor apparatus (Optomotry) at optimal drift velocities for photopic and scotopic vision, respectively. Electroretinographic (ERG) analysis was performed in anesthetized mice under scotopic and photopic conditions.

 
Results:
 

Trpc1 mRNA accounted for 78 ± 15% of the total canonical transcriptome in the mouse retina. Loss of rods in P90 Pde6brd1 retinas was associated with 77 ± 7% reduction in Trpc1 mRNA content. The amplitude of scotopic OKR responses in Sv129 wild type controls was 0.252 ± 0.003 cycles/degree. Scotopic acuity was increased in TRPC1-/- (0.272 ± 0.009 c/deg) and TRPC3-/- (0.292 ± 0.007 c/deg) animals. Given 88 ± 10% compensatory upregulation of Trpc3 mRNA in TRPC1-/- retinas we generated TRPC1/3-/- animals; their OKR was 0.308 ± 0.003 c/deg, significantly increased compared to controls (P<0.001). The scotopic a-wave was increased in TRPC1-/- eyes at high flash intensities and in TRPC1/3-/- eyes at all flash intensities (P<0.01). Increased b-wave amplitudes (20 ± 3%) were measured in double KO eyes. Photopic OKR responses in TRPC1-/- and TRPC3-/- animals were statistically indistinguishable from controls (0.412 ± 0.006 c/deg); however, a significant increase in photopic acuity was observed in TRPC1/3-/- animals (0.442 ± 0.005 cycles/deg).

 
Conclusions:
 

These results show that TRPC1 channels, possibly in heteromeric association with TRPC3, negatively regulate rod signaling and scotopic visual behavior in mice. Influx of calcium through TRPC1/3 channels appears to modulate the photosensitivity, neurotransmission and/or the dynamic range of light-evoked signals in wild type rods.

 
Keywords: calcium • photoreceptors: visual performance • ion channels 
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