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B.A. Hughes, D. Yang, A. Swaminathan, B. Pattnaik; Expression of KCNQ Potassium Channels in Primate Retinal Pigment Epithelium . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2915.
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© ARVO (1962-2015); The Authors (2016-present)
We reported previously the expression in human and bovine RPE cells of a sustained, outwardly rectifying K+ current whose kinetics and voltage activation range resemble those of M–currents in excitable cells, which are mediated by channels composed of pore–forming KCNQ and auxiliary KCNE subunits. The objectives of this study were to determine whether KCNQ and KCNE genes are expressed in primate RPE and to test the sensitivity of M–type K+ currents in native monkey RPE cells to KCNQ channel blockers.
RT–PCR was performed on RNA isolated from monkey and human RPE sheets using specific primer pairs for human KCNQ1–5 and KCNE1–5. Whole–cell currents were recorded from freshly dissociated monkey RPE cells at room temperature. The standard pipette solution contained (in mM): 30 KCl, 83 K–gluconate, 10 HEPES, 5.5 EGTA, 0.5 CaCl2, and 4 Mg–ATP, pH 7.2. The control bath solution contained 135 NaCl, 5 KCl, 10 HEPES, 10 glucose, 1.8 CaCl2, and 1.0 MgCl2, pH 7.4.
Appropriately–sized products were detected in monkey and human RPE for KCNQ1, KCNQ4, and KCNQ5 and in human RPE for KCNE2 and KCNE3. In patch–clamp experiments on monkey RPE cells, linopirdine, a specific blocker of KCNQ channels, inhibited the M–type K+ current in a concentration–dependent manner, with an IC50 of about 300 nM. In contrast, TEA, a blocker of KCNQ1 and KCNQ4 but not KCNQ5 channels, had little effect, blocking <20% of the M–type K+ current at a concentration of 135 mM.
The results demonstrate that KCNQ1, KCNQ4, KCNQ5, KCNE2 and KCNE3 are expressed in the primate RPE. The high sensitivity of the M–type K+ current to block by linopirdine and low sensitivity to TEA suggest that it is mediated by KCNQ5 channels. We conclude that KCNQ5 channels make a major contribution to the membrane K+ conductance in primate RPE, where they function in K+ transport and setting the membrane potential.
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