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C. W. Morgans, S.-X. Zheng, I. Strycharska-Orczyk, R. L. Brown, B. Jeffrey, R. M. Duvoisin; TRPM1 Localization in Retinal ON-Bipolar Cells in the Macaque and Mouse. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4131.
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The TRPM1 cation channel has been shown to mediate the depolarizing response of retinal ON-bipolar cells to light. This channel is negatively coupled to the ON-bipolar cell metabotropic glutamate receptor, mGluR6, such that when glutamate is bound to mGluR6, the channel is closed. This study examines the subcellular distribution of TRPM1 in ON-bipolar cells in relation to mGluR6 and other synaptic markers.
The expression and subcellular localization of TRPM1 channels was assessed by immunofluorescence confocal microscopy in mouse and macaque retina, and TRPM1-transfected HEK293 cells. Double and triple immunofluorescent labeling was used to compare the distribution of TRPM1 to mGluR6, PKC (rod bipolar cells), Galphao (ON-bipolar cells), calbindin D (horizontal cells), ctbp2 and bassoon (photoreceptor synaptic ribbons).
TRPM1 is localized to ON-bipolar cells in both the mouse and macaque retina. Strong immunoreactivity is present in the cell bodies and dendrites, and weaker immunoreactivity is present in the ON-bipolar cell synaptic terminals. Within the dendrites, the distributions of TRPM1 and mGluR6 are spatially separate, with mGluR6 having a more distal localization in the tips of the dendrites. Within the Macaque OPL, the TRPM1 antibody labels crescent shaped structures, but these are distinct from synaptic ribbons and horizontal cell processes. Comparison with PKC immunofluorescence, indicates that TRPM1 is not at the plasma membrane in the ON-bipolar cell bodies. Similarly, TRPM1, when transfected alone, was found to be located beneath the plasma membrane in HEK293 cells.
TRPM1 is localized to ON-BPC cell bodies, dendrites, and terminals. TRPM1 does not overlap with the distribution of mGluR6, which is closer to the tips of the dendrites. Within the cell bodies, TRPM1 appears to have a sub-plasma membrane localization.
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