Potassium currents in cultured rabbit retinal pigment epithelial cells |
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Authors: | Q Tao P E Rafuse M E M Kelly |
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Institution: | (1) Department of Pharmacology, Tupper Medical Building, Dalhousie University, B3H 4H7 Halifax, Nova Scotia, Canada;(2) Department of Ophthalmology, Dalhousie University, Halifax, Nova Scotia, Canada |
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Abstract: | Membrane potential and ionic currents were studied in cultured rabbit retinal pigment epithelial (RPE) cells using whole-cell patch clamp and perforated-patch recording techniques. RPE cells exhibited both outward and inward voltage-dependent currents and had a mean membrane capacitance of 26±12 pF (sd, n=92). The resting membrane potential averaged ?31±15 mV (n=37), but it was as high as ?60 mV in some cells. When K+ was the principal cation in the recording electrode, depolarization-activated outward currents were apparent in 91% of cells studied. Tail current analysis revealed that the outward currents were primarily K+ selective. The most frequently observed outward K+ current was a voltage- and time-dependent outward current (I K) which resembled the delayed rectifier K+ current described in other cells. I K was blocked by tetraethylammonium ions (TEA) and barium (Ba2+) and reduced by 4-aminopyridine (4-AP). In a few cells (3–4%), depolarization to ?50 mV or more negative potentials evoked an outwardly rectifying K+ current (I Kt) which showed more rapid inactivation at depolarized potentials. Inwardly rectifying K+ current (I KI) was also present in 41% of cells. I KI was blocked by extracellular Ba2+ or Cs+ and exhibited time-dependent decay, due to Na+ blockade, at negative potentials. We conclude that cultured rabbit RPE cells exhibit at least three voltage-dependent K+ currents. The K+ conductances reported here may provide conductive pathways important in maintaining ion and fluid homeostasis in the subretinal space. |
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Keywords: | Voltage-dependent K+ currents Retinal pigment epithelial cells Patch clamp |
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