title: K+ and Cl- currents in freshly isolated rat osteoclasts.
abstract: Membrane electrical properties of freshly isolated rat osteoclasts were studied using patch-clamp recording methods. Characterization of the passive membrane properties indicated that the osteoclast cell membrane behaved as an isopotential surface. The specific membrane capacitance was 1.2 +/- 0.3 microF/cm2 (mean +/- SD), with no difference between cells plated on glass and those adhering to a permeable collagen substrate. The current/voltage (I/V) relationship of all cells showed inward rectification and I/V curves shifted 51 mV positive per tenfold increase of [K+]out, indicating an inwardly rectifying K+ conductance. The voltage dependence of the K+ chord conductance (gK) also shifted positive along the voltage axis, and the maximum conductance increased, with elevation of [K+]out. gK for cells bathed in 4.7 mM [K+]out increased e-fold per 12 mV hyperpolarization, and half-maximal activation was at -89 mV. Approximately 18% (50 pS/pF) of the maximum gK was active at -70 mV. Inward single-channel currents were recorded in cell-attached patches at hyperpolarizing potentials. With symmetrical K+, channel conductance was 25 +/- 3 pS and reversal was close to the K+ equilibrium potential, consistent with this K+ channel underlying the whole-cell K+ currents. With both conventional whole-cell and perforated-patch recording, no voltage-activated Ca2+ current was detected. In approximately 30% of osteoclasts studied, an outwardly rectifying current was observed, which was reversibly blocked by 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS). This DIDS- and SITS-sensitive current reversed direction at the chloride equilibrium potential. We conclude that an inwardly rectifying K+ current is present in all rat osteoclasts and that some osteoclasts also exhibit an outwardly rectifying Cl- current. Both these membrane conductances may play an important physiological role by dissipating the potential that arises from the electrogenic transport of H+ across the ruffled membrane of the osteoclast.
authors.affiliation: Department of Physiology, University of Western Ontario, London, Canada.
authors.forename: S M
authors.initials: SM
authors.lastname: Sims
authors.forename: M E
authors.initials: ME
authors.lastname: Kelly
authors.forename: S J
authors.initials: SJ
authors.lastname: Dixon
mesh_terms: D000818:Animals; D000838:Anions / Q000378:metabolism; D002469:Cell Separation; D018118:Chloride Channels; D003094:Collagen; D004594:Electrophysiology; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000502:physiology*; D009994:Osmolar Concentration; D010010:Osteoclasts / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats
chemical_list: D000838:Anions; D018118:Chloride Channels; D008565:Membrane Proteins; D015221:Potassium Channels; D003094:Collagen; D011188:Potassium