title: Calcium-activated potassium current in cultured rabbit retinal pigment epithelial cells.
abstract: Calcium-activated potassium current was studied in cultured rabbit retinal pigment epithelial (RPE) cells using whole-cell and single channel patch-clamp recording techniques. When K+ was the principal cation in the electrode, depolarizing voltage steps from a holding potential of -60 mV activated outwardly rectifying current. Outward K+ current was increased by the Ca2+ ionophore ionomycin and reduced when the extracellular Ca2+ concentration was decreased from 2.5 mM to 100 nM in the presence of ionomycin. Outward K+ current recorded in the presence of ionomycin was blocked by iberiotoxin and by charybdotoxin. Single channel recording from cell-attached and excised membrane patches revealed a large conductance Ca2+-activated K+ (K(Ca)) channel. Identification of K(Ca) channels was based on: 1) the voltage-dependence of channel opening; 2) the large unitary conductance (> 200 pS with symmetrical 130 mM K+); 3) the dependence of the reversal potential on the K+ gradient; and 4) increased channel opening after exposure of the cytosolic surface of excised membrane patches to elevated Ca2+. These results demonstrate that Ca2+-activated K+ channels are present in rabbit RPE cells and may play an essential role in the regulation of membrane potential and ion transport.
authors.affiliation: Department of Pharmacology, Dalhousie University, Halifax, NS, Canada.
authors.forename: Q
authors.initials: Q
authors.lastname: Tao
authors.forename: M E
authors.initials: ME
authors.lastname: Kelly
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D018999:Charybdotoxin / Q000494:pharmacology; D004553:Electric Conductivity; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D014118:Toxins, Biological / Q000494:pharmacology
chemical_list: D007476:Ionophores; D010455:Peptides; D015221:Potassium Channels; D014118:Toxins, Biological; D018999:Charybdotoxin; D015759:Ionomycin; C064719:iberiotoxin; D011188:Potassium; D002118:Calcium