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S. Mergler, H. Yang, F. Zhang, Z. Pan, U. Pleyer, P. Reinach; Transient Receptor Potential Vanilloid 1 (TRPV1) Functional Expression in Human Corneal Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3497.
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TRPV1, is a member of the vanilloid-type transient receptor potential ion channel family. It is activated by heat or by the agonist (capsaicin). Such activation induces a transient rise in intracellular free calcium concentration ([Ca2+]i). This increase occurs as a result of an influx of Ca2+ through the plasma membrane via this non-selective cation channel. We identified TRPV1 expression and characterized its functional activity in human corneal epithelial cells (HCEC).
TRPV1 mRNA expression was detected by RT-PCR and protein expression was confirmed by Western blotting. Ca2+ transients were measured by single cell fluorescence imaging. The whole-cell patch-clamp technique was used to monitor capsaicin-mediated stimulation of non-selective cation channel activity. Putative L-type Ca2+ channel activity was inhibited with nifedipine (5 µM).
In a Na+ and K+-free solution, there were nearly no calcium responses during exposure to capsaicin (10 µM). In a Ringer solution with 5 µM nifedipine, the calcium base line (control) declined. However, capsaicin clearly induced a calcium increase, which was not affected by nifedipine blockade of L-type Ca2+ channels. In a standard extracellular solution described by Voets et al. (Nature 2004), capsaicin induced the largest reproducible increase in [Ca2+]i compared to use other solutions. Finally, extracellular application of 10 µM capsaicin elicited increases in non-selective cation channel outward currents in HCEC from 0.604 ± 0.052 nA to 1.127 ± 0.264 nA (± SEM; n = 4).
Putative activation of TRPV1 needs sodium, potassium and calcium as charge carriers. Interestingly, L-type Ca2+ channels are expressed in HCEC. However, blockade of L-type channels does not influence the capsaicin-induced [Ca2+]i increase. In HCEC, capsaicin is a potent TRPV1 activator, which induces nearly 2-fold increases in non-selective cation channel currents.
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