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2018 Abstracts

Polymodal TRP channels functionally co-localize in a subset of mouse retinal ganglion cells

Monika Lakk; Derek Young, University of Utah

Polymodal TRP channels functionally co-localize in a subset of mouse retinal ganglion cells Derek Young, Monika Lakk, David Križaj Department of Ophthalmology & Visual Sciences, Moran Eye Institute, University of Utah, Salt Lake City, UT Introduction Transient receptor potential vanilloid (TRPV) channels are polymodal, nonselective cation channels that can be activated by multiple stimuli (temperature, osmotic stress, mechanical stretch, chemical factors). Although these channels regulate signaling in nonexcitable cells, their function in the vertebrate visual system is essentially unknown. Also, we do not know whether different TRP isoforms interact in retinal ganglion cells (RGCs) and how they might be impacted in optic neuropathies (glaucoma). Methods Wild type (C57BL/6) mouse retinas were isolated and acutely dissociated with papain in L-15 medium. Cells were plated, and loaded with Fura-2 AM before Ca-imaging. 340 and 380 nm excitation light was from a Lambda DG-4 wavelength switcher. Emissions were collected at 510 nm. Immunopanned (IP) RGCs and quantitative RT-PCR were used to measure the mRNA levels. Immunolabeling was applied to visualize and determine the receptor connectivity in the targeted cells. Results Administration of TRPV1 receptor agonist capsaicin (10µM) increased the [Ca2+]i levels (0.45±0.07) in a subset of RGCs (11.25%), whereas another cohort of RGCs (40.6%) showed [Ca2+]i responses (0.51±0.05) comparable to the effects of the TRPV4 receptor agonist GSK1016790A (25 nM). Capsaicin had no effect to baseline [Ca2+]i levels. A third functional type of RGC showed [Ca2+]i elevations for both agonists (9.75%). At the end of each experiment, RGCs were briefly exposed to glutamate (100µM) and high K+ solution (35 mM) to confirm their identity and viability. Immunolabeling on vertical sections confirmed that some RGC express TRPV4, vs. TRPV1 vs. TRPV1 + TRPV4 channels. Summary These data demonstrate that, the vanilloid TRPV1 and TRPV4 isoforms are differentially expressed in RGCs. The nociceptive TRPV1channel in the retina is localized in a region-specific manner; it shows spatial and functional overlap with TRPV4 in a subset of cells. These data suggest that RGCs sense ambient information from temperature, mechanical stress (pressure, stretch, swelling), pH and endocannabinoids in a polymodal yet cell type-specific manner. The pattern of vanilloid channel expression may determine their susceptibility to pathological stimuli in blinding diseases such as ischemia, diabetic retinopathy and glaucoma.