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G. Li, W. Liedtke, P. Challa, C. Luna, D. L. Epstein, P. Gonzalez, P. Liton; Expression of Transient Receptor Potential (TRP) Channels in the Outflow Pathway and Ciliary Body of Porcine Eyes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2066.
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Members of the Transient Receptor Potential (TRP) Channels subfamilies C (canonical), V (vanil-loid receptor), M (melastatin) have been reported to play an important role in functions such as mechanoreception and response to oxidative stress in a variety of tissues. Our objective was to identify the members of these TRP channel subfamilies expressed in the ciliary body (CB) and trabecular meshwork (TM) cells.
For analysis of expression in tissue samples, anterior segments of fresh porcine eyes were fixed in RNAlater (Ambion) and the TM and CB were dissected. To investigate the effects of chronic oxidative stress, primary cultures of porcine TM cells were exposed to hyperoxic conditions for 15 days and compared to parallel control cultures. Total RNA from dissected tissues or cultured cells was extracted with RNAeasy mini kit (Qiagen). Real-time Q-PCR reactions were performed using iQ SYBR Green Supermix (Biorad, Hercules, CA) in a BIO-RAD iCycler iQ system (BioRad, Hercules, CA). The size of the PCR products was visualized by agarose gel electrophoresis.
The TRP protein most highly expressed in the CB was TRPM3, a gene known to be expressed in human brain and human kidney, and which is known to be involved in renal osmo-homeostasis. Members of the TRPC and TRPV subfamilies were expressed only at low levels in the CB. The more highly expressed TRP genes in the TM included: TRPC4, which is a key determinant of increased microvascular permeability; TRPC6, involved in mechanotransduction in smooth muscle cells and associated with glomerulosclerosis; TRPM4, which is believed to be involved in sensing shear stress and stretching in vascular endothelial cells; and TRPM7, a stretch- and swelling-activated cation channel regulator of actomyosin contractility and cell adhesion. The expression of TRPC6 showed a statistically significant upregulation of more than 5 fold in TM cells incubated under chronic oxidative stress compared to the control.
Because of the roles reported in other tissues for the TRP genes expressed in the CB and TM, these genes may play a relevant role in the modulation of both the production of aqueous humor and the resistance to aqueous humor outflow in the TM. Therefore, the identification of TRP proteins expressed in the CB and TM may open new avenues for pharmacological intervention in glaucoma.
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