title: The inward rectifier K+ current underlies oscillatory membrane potential behaviour in bovine pigmented ciliary epithelial cells.
abstract: 1. Fresh bovine, pigmented ciliary epithelial cells possess an inward rectifier current activated by hyperpolarization. This current was investigated using whole-cell patch-clamp techniques. At the holding potential of -70 mV, and with EK (potassium equilibrium potential) set at -84 mV, a small outward current flowed through the inward rectifier that was sensitive to external K+, becoming more outward in 0.5 mM K+ and progressively more inward in 20 and 50 mM K+. 2. The inward rectifier showed V-EK dependence; increasing [K+]o increased the inward conductance from 1.28 nS in 5 mM K+ to 7.42 nS in 50 mM K+. The conductance at a given V-EK was proportional to the square root of [K+]o. 3. It was blocked by external Cs+ but replacing K+ in the pipette with Cs+ blocked only outward ion movement through the inward rectifier. Inward rectification was also blocked by Ba2+ (85% with Ki (concentration giving half-maximal inhibition) = 3.1 x 10(-5) M) and TEA+ (74% with Ki = 2.9 x 10(-4) M). 4. The activation time constant was voltage dependent, decreasing from 5 ms to 0.7 ms over the voltage range -90 to -170 mV. With increasing hyperpolarization the current exhibited time-dependent decay. The time constant for this process was voltage sensitive but the steady-state inactivation was independent of external [K+]. 5. The current disappeared in culture within 8 days. 6. Solution flow over the cell inactivated the inward rectifier, a property that may be related to [K+]o. 7. In current clamp the cells exhibited an unstable region at a potential of around -70 mV. Once in this region oscillations and regenerative hyperpolarizing potentials were observed. This behaviour was eliminated by treatments that blocked (Cs+, Ba2+) or removed (0.5 mM K+) active inward rectification. 8. It is suggested that these oscillations may represent a process of cation loading, the first step in the secretion of aqueous humour.
authors.affiliation: Department of Physiology, University of Wales, Cardiff.
authors.forename: J W
authors.initials: JW
authors.lastname: Stelling
authors.forename: T J
authors.initials: TJ
authors.lastname: Jacob
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D002924:Ciliary Body / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004848:Epithelium / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D001464:Barium; D011188:Potassium