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NC Welch, S Barnes, ME M Kelly; Calcium and Calcium-Activated Potassium Currents in Müller Cells Isolated From Tiger Salamander Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4757.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Müller cells, whose resting membrane potential is set by Kir channels, also express Ca and K(Ca) channels. Here we characterize some pharmacological properties of these ion channel types in Müller cells. Methods: Whole-cell and single channel patch clamp recordings were made from acutely isolated Müller cells. For whole cell and single channel K(Ca) channel studies, 2.5 mM and 100 mM external K+-containing solutions were used, respectively, with 100 mM external Ba2+ to block Kir channels. Ca channel currents were recorded in 10 mM Ba2+ with Cs+ in the pipette. Results: In the presence of 100 µM Ba2+, outwardly rectifying K(Ca) channel currents were identified in whole cell recordings. Measured at +60 mV, the outward current was reduced by 41% ± 9% (mean ± SD) by tetraethylammonium (TEA; 1mM; n=3) and enhanced by 28% ± 15% by the calcium ionophore A23187 (1 µM; n=6). The A23187-enhanced K(Ca) channel current was inhibited by 70% ± 14% by the large conductance BK channel blocker iberiotoxin (50 nM; n=3). Consistent with the presence of BK channels, unitary currents recorded from cell-attached and excised patches revered near 0 mV in symmetric K+ solutions and had a slope conductance of ∼200 pS. Ca channel currents were characterized in whole cell patch clamp recordings, using Ba2+ as the charge carrier. Ca channel currents were observed positive to -20 mV with a peak current amplitude of 1.4 ± 0.5 pA/pF (n=22). Cd2+ reduced Ca channel current by 81% ± 10% (10 µM n=4). The L-type Ca channel blocker, nisoldipine, reduced Ca channel currents by 66% ± 13% (1 µM; n=3) while the T-channel blocker, pimozide, blocked Ca channel currents by 84% ± 11% (1 µM; n=5). Carbenoxolone, an agent used to block gap junction channels, suppressed Ca channel currents by 48% ± 14% (100 µM; n=5). Conclusion: Müller cells express typical BK channels but Ca channels seem to have a distinct pharmacology. The roles of these channels in the physiological activity of Müller cells and their pharmacological properties deserve attention when testing agents in the retina.
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