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H. Wang, B. R. Pattnaik, B. A. Hughes; Activation of M-Type Current in Mouse RPE Cells by Zinc Pyrithione. Invest. Ophthalmol. Vis. Sci. 2010;51(13):495.
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© ARVO (1962-2015); The Authors (2016-present)
We have shown previously that freshly isolated human, monkey, and bovine RPE cells exhibit an M-type K+ current, which recent evidence suggests is mediated by KCNQ/Kv7 channels. The purpose of this study was to determine whether M-type currents are also expressed in mouse RPE.
RPE cells from C57BL/6 mice were isolated enzymatically with papain. Whole-cell currents were recorded using the patch-clamp technique. M-type current was identified by its characteristic tail currents and kinetics. The pipette solution contained (in mM) 100 K gluconate, 30 KCl, 5 HEPES, 5.5 EGTA-KOH, 0.5 CaCl2, 4 Mg-ATP (pH 7.2) and the control bath solution consisted of (in mM) 5 KCl, 135 NaCl, 10 HEPES, 10 glucose, 1.8 CaCl2, and 1 MgCl2 (pH 7.4).
Mouse RPE cells had an average membrane potential of -55.2 ± 3.3 mV (mean ± SE, n = 9) and exhibited a prominent inwardly rectifying K+ current, but no M-type K+ current. Exposure of cells to 10 µM zinc pyrithione (ZnPy), a potent KCNQ channel opener, activated M-type current in every cell tested, with a maximal conductance of 5.1 ± 1.0 nS (n = 8) and a half-maximal voltage for activation of -58.1 ± 5.5 mV (n = 8). Erbstatin (20 µM), a Src tyrosine kinase inhibitor, also activated M-type current in resting mouse RPE cells, albeit to a lesser extent than did ZnPy.
Our findings that M-type current is absent in freshly isolated mouse RPE cells and that it can be activated by ZnPy suggest that KCNQ channels are present but inactivated at rest. Tyrosine phosphorylation of these channels might contribute to this inactivation, but it is likely that other mechanisms are also involved.
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