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TRPV1: Contribution to Retinal Ganglion Cell Apoptosis and Increased Intracellular Ca²⁺ with Exposure to Hydrostatic Pressure

From the Vanderbilt Eye Institute, Vanderbilt University Medical Center, Nashville, Tennessee.

PURPOSE. Elevated hydrostatic pressure induces retinal ganglion cell (RGC) apoptosis in culture. The authors investigated whether the transient receptor potential vanilloid 1 (TRPV1) channel, which contributes to pressure sensing and Ca²⁺-dependent cell death in other systems, also contributes to pressure-induced RGC death and whether this contribution involves Ca²⁺.

METHODS. trpv1 mRNA expression in RGCs was probed with the use of PCR and TRPV1 protein localization through immunocytochemistry. Subunit-specific antagonism (iodo-resiniferatoxin) and agonism (capsaicin) were used to probe how TRPV1 activation affects the survival of isolated RGCs at ambient and elevated hydrostatic pressure (+70 mm Hg). Finally, for RGCs under pressure, the authors tested whether EGTA chelation of Ca²⁺ improves survival and whether, with the Ca²⁺ dye Fluo-4 AM, TRPV1 contributes to increased intracellular Ca²⁺.

RESULTS. RGCs express trpv1 mRNA, with robust TRPV1 protein localization to the cell body and axon. For isolated RGCs under pressure, TRPV1 antagonism increased cell density and reduced apoptosis to ambient levels (P 0.05), whereas for RGCs at ambient pressure, TRPV1 agonism reduced density and increased apoptosis to levels for elevated pressure (P 0.01). Chelation of extracellular Ca²⁺ reduced RGC apoptosis at elevated pressure by nearly twofold (P 0.01). Exposure to elevated hydrostatic pressure induced a fourfold increase in RGC intracellular Ca²⁺ that was reduced by half with TRPV1 antagonism. Finally, in the DBA/2 mouse model of glaucoma, levels of TRPV1 in RGCs increased with elevated IOP.

CONCLUSIONS. RGC apoptosis induced by elevated hydrostatic pressure arises substantially through TRPV1, likely through the influx of extracellular Ca²⁺.

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