Potassium currents in cultured rabbit retinal pigment epithelial cells.
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 (IK) which resembled the delayed rectifier K+ current described in other cells. IK 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 (IKt) which showed more rapid inactivation at depolarized potentials. Inwardly rectifying K+ current (IKI) was also present in 41% of cells. IKI 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.
Tao
Q
Q
Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada.
Rafuse
P E
PE
Kelly
M E
ME
D000818:Animals; D002478:Cells, Cultured; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D008564:Membrane Potentials / Q000187:drug effects; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology / Q000502:physiology; D015221:Potassium Channels / Q000502:physiology*; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors
D015221:Potassium Channels; D012964:Sodium; D011188:Potassium