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S. Wimmers, S. Seyler, O. Strauss; Heat Sensing by the Retinal Pigment Epithelium in the Eye Through Activation of Trpv Channels. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3976.
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© ARVO (1962-2015); The Authors (2016-present)
The retinal pigment epithelium (RPE) fulfils a variety of tasks which are essential for retinal function. This requires a multitude of different regulatory pathways and the ability to react to a large variety of stimuli. One of these stimuli is heat. Puposer of this study was to identify the heat-sensing pathway in the RPE.
The expression profile of probable heat-sensing ion channels was investigated by RT PCR. Responses from RPE cells to heat-stimuli were investigated by measurements of intracellular free Ca2+ with fura-2 and by the patch-clamp technique.
RT-PCR analysis of cDNA from freshly isolated human RPE cells revealed the expression of TRPV1,2, 3 and 4 channels. Increasing the temperature from room temperature to either 45°C or 56°C led to an increase in [Ca2+]i in human RPE cells in primary culture. These temperature-induced rises in intracellular Ca2+ were blocked by 100 µM La3+ or 1 µM ruthenium-red. Application of the TRPV1 opener capsaicin (1 µM) did not increase [Ca2+]i whereas application of the TRPV opener 2-ABP [Ca2+]i. Whole-cell currents in ARPE-19 cells showed at a holding potential -40 mV, the transient activation of an inward-current by rising the temperature to 45°C. In the presence of 20 µM ruthenium-red, rising the temperature to 45°C failed to activate this inward current.
In summary, we conclude that increase in the temperature leads to rises in [Ca2+]i by activation of TRPV2 or TRPV3 channels. Thus, the RPE is able to sense heat. Since the RPE absorbs the major of the light energy which is focused by a lens onto the retina heat sensing by the RPE is a novel important mechanism to adopt its function to changes in the light intensity.
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