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D. Krizaj; Expression of Transient Receptor Potential Channels (TRPCs) in the Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5344.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: TRPs are Ca–permeable plasma membrane channels that play a key role in invertebrate vision and in sensory transduction of vertebrate primary sensory neurons. The channels can be activated by different signaling pathways, including heteromeric G proteins and/or depletion of intracellular Ca stores. Last year we characterized TRPC expression in salamander retina using anatomical and functional techniques. Here we extend those studies to analyze TRPCs in the mouse retina. Methods: Mouse retinas were fixed in 4% paraformaldehyde and immunostained with antibodies raised against epitopes from TRPC isoforms 1, 4, 5 and 6. Double–immunostaining with cell type – specific markers was used to localize TRPC signals to defined classes of retinal neuron. The antibodies were visualized with a confocal microscope. In parallel experiments, expression of TRPC antigens was checked with Western blots. For each antibody, control experiments were performed using specific neutralizing antibodies. Results:Western blots show expression of all 4 TRPCs in the mouse retina. TRPC1 was observed in both plexiform layers with an especially prominent signal in horizontal cell dendritic knobs and in inner segment stalks of photoreceptors. At higher confocal gains, a signal was seen in the inner nuclear layer, possibly corresponding to cell bodies of bipolar and amacrine cells. TRPC4 was detected in both plexiform layers with a strong label at the outer limiting membrane. A subset of amacrine and ganglion cell perikarya was also immunostained with TRPC4. A diffuse cytoplasmic signal in bipolar cell and ganglion cell bodies was seen with the TRPC5 antibody. Finally, TRPC6 was selectively expressed in the plasma membrane surrounding cell bodies of rod photoreceptors, but was excluded from synaptic terminals or inner segment stalks. Double–labeling with antibodies that recognize the alpha subunit of L–type calcium channels suggested a marked compartmentalization of calcium influx mechanisms in mouse rods; the calcium channels appeared to be strongly expressed in synaptic terminals and in inner segment stalk region, but were excluded from the cell body. In contrast, TRPC6 signal was detected exclusively in the cell body of rods. Diffuse cytoplasmic staining was observed in perikarya localized to the inner nuclear layer. Conclusions:These results suggest a new pathway of calcium ion entry into retinal neurons. In the retina, TRPCs appear to be expressed in a cell type–specific manner. Given the multiplicity of signaling mechanisms that can activate TRPCs, our results add another layer to complexity of Ca homeostatic mechanisms in retinal cells.
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