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Robert Duvoisin, Wei-Hong Xiong, Brian Reed, Catherine Morgans, R Brown; TRPM3 expression in the mouse retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3384.
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© ARVO (1962-2015); The Authors (2016-present)
TRP channels are a large family of cation permeable ion channels that serve crucial functions in sensory systems by transducing changes in the environment into voltage and calcium signals in the cell. Within the retina, two closely related members of the melastatin TRP family, TRPM1 and TRPM3, are highly expressed. TRPM1 has been shown to be required for the depolarizing response to light of ON-bipolar cells, but the role of TRPM3 in the retina is unknown.
To investigate the function of TRPM3, RT-PCR from total retina RNA yielded overlapping fragments that were assembled into a full-length mouse TRPM3 cDNA. An antibody was generated against the C-terminus of TRPM3 and used to localize TRPM3 in the retina by immunofluorescence. Patch-clamp recordings of TRPM3 currents were obtained from transfected HEK293 cells and retinal ganglion cells. TRPM3 activity was also measured by calcium imaging of dissociated retinal ganglion cells.
TRPM3 transiently expressed in HEK293 cells gave rise to pregnenolone sulfate (PS) activated channels that were permeable to sodium and calcium. Immunolabeling of mouse retina revealed that TRPM3 is present in the ganglion cell layer, the inner plexiform layer (IPL), and in the retinal pigment epithelium (RPE). Within the IPL, TRPM3 immunofluorescence was stronger in the OFF sublamina. Specificity of the antibody staining was confirmed by the absence of immunostaining in the retinas of TRPM3-/- mice. Electroretinogram recordings showed that the scotopic a- and b-waves of TRPM3-/- mice are normal indicating that TRPM3 does not play a major role in visual processing in the outer retina. Calcium imaging of immunopurified ganglion cells revealed PS-stimulated currents in ~40% of cells in wild-type and TRPM1-/- mice; these PS-stimulated currents were blocked by mefanamic acid and were absent in TRPM3-/- mice. Patch-clamp recordings of ganglion cells in a retinal whole mount preparation revealed PS-sensitive currents in OFF-ganglion cells that were absent in the TRPM3-/- retina.
These data suggest a role for TRPM3 in the RPE and in modulating the light responses of ganglion cells, particularly OFF-ganglion cells.
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