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Daniel A. Ryskamp, Tunde Molnar, Peter Barabas, Wei Xing, David Krizaj; Intrinsic Mechanosensation In Mammalian Retinal Ganglion Cells Is Mediated By Trpv4. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3091.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal ganglion cells (RGCs) are immersed within a mechanically active environment in which they must constantly cope with and adapt to hydrostatic pressure and osmotic stress. The purpose of this project was to identify the molecular mechanism that underlies the mechanosensitive properties of mouse RGCs and to characterize the role of plasma membrane stretch in RGC Ca2+ homeostasis.
Retinas from C57BL/6J mice were used for calcium imaging experiments, Western blotting, and fluorescent immunolabeling. RGCs expressing CFP driven by the thy1 promoter or stained with Brn3 antibodies were included in the morphology analysis. TRPV4 signals were assessed with validated antibodies in wild type and knockout animals. RGC soma diameter measurements were performed using confocal and CCD camera-based microscope setups. [Ca2+]i was measured in fura-2 loaded RGCs. Pressure stimuli were mimicked by hypotonic membrane stretch.
Hypotonic saline elevated [Ca2+]i in presumed RGCs by 439 ± 59 nM. The diameters of these cells (8.9 ± 1.3 um) corresponded to diameters of dissociated thy1-CFP -positive cells (10.2 ± 1.8 um), dissociated Brn3a-immunopositive cells (10.9 ± 0.9 um), as well as Brn3a-positive RGCs in retinal slices (10.4 ± 2.0 um). All Brn3a-immunopositive cells were immunopositive for TRPV4 (N = 81). Non-selective TRP channel blockers Ruthenium Red (10 uM) and gadolinium (100 uM) reduced the amplitude of stretch-induced responses (p < 0.0001 and p < 0.05, respectively) and TRPV4 agonist-induced [Ca2+]i elevations. Cells responding to osmotic pressure were sensitive to stimulation with selective TRPV4 agonists whereas capsaicin, a TRPV1 agonist, had no effect on [Ca2+]i in acutely dissociated RGCs (N > 110).
These results demonstrate that mouse RGCs are intrinsically mechanosensitive. Molecular transduction of mechanical stimuli involves TRPV4, a polymodal pressure- and osmosensitive channel which provides prominent modulation of RGC Ca2+ homeostasis and excitability. Our findings may have implications for blinding diseases associated with pathological changes in intraocular pressure.
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