Inwardly rectifying K+ channel
Outwardly rectifying Cl− channel
Springer Online Journal Archives 1860-2000
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 μF/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 (g K) also shifted positive along the voltage axis, and the maximum conductance increased, with elevation of [K+]out. g K for cells bathed in 4.7 mM [K+]out increased e-fold per 12mV hyperpolarization, and half-maximal activation was at −89 mV. Approximately 18% (50 pS/pF) of the maximum g K 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′-isothiocyanostilbene2,2′-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.
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