Outwardly rectifying chloride current in rabbit osteoclasts is activated by hyposmotic stimulation.

Abstract

1. We characterized chloride currents in freshly isolated rabbit osteoclasts using whole‐cell and single channel patch‐clamp recording configurations. Depolarization activated an outwardly rectifying current in 40‐50% of cells, distinct from the inwardly rectifying K+ current we have previously reported in osteoclasts. 2. The outwardly rectifying current persisted under conditions where all K+ currents were blocked. Furthermore, the outward current was reversibly inhibited by Cl‐ transport blockers 4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid (SITS); 4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid (DIDS); 4,4'‐dinitrostilbene‐2,2'‐disulphonic acid (DNDS); and niflumic acid. The blocked current had a reversal potential close to the predicted chloride equilibrium potential and was dependent on the chloride concentration gradient. 3. In those osteoclasts in which outwardly rectifying current was not initially apparent, exposure to hyposmotic extracellular solution resulted in its reversible activation. The induced current was due to Cl‐, based on its reversal close to the chloride equilibrium potential and sensitivity to blockade by Cl‐ channel inhibitors. The hyposmotically induced current could be activated in Ca(2+)‐free solutions containing 0.2 mM EGTA. 4. When studied in the current‐clamp configuration, hyposmotic stimulation caused depolarization from ‐76 +/‐ 5 to ‐5 +/‐ 6 mV (mean +/‐ S.D., n = 7). 5. Unitary Cl‐ currents were recorded in the cell‐attached patch configuration at positive potentials. Single channels had a slope conductance of 19 +/‐ 3 pS (n = 5). Reduction of the external [Cl‐] shifted the current‐voltage relationship in the positive direction, supporting the conclusion that these were Cl‐ currents. Like the whole‐cell currents, single channel Cl‐ currents were activated by exposure of cells to hyposmotic bathing solution. 6. We conclude that rabbit osteoclasts express an outwardly rectifying Cl‐ current that can be activated by osmotic stress. Cl‐ channels may play a role in cell volume regulation and may also provide conductive pathways for dissipating the potential difference that arises from electrogenic proton transport during bone resorption.

Chloride Channels Regulate HIT Cell Volume but Cannot Fully Account for Swelling-Induced Insulin Secretion

“…3A), followed by a spontaneous regulatory volume decrease (RVD). RVDs have been observed previously after the application of hypotonic solutions to rat ␤-cells (36,37), RINm5F cells (38), and mouse ␤-cells (39). When the hypotonic solution also contained 100 mol/l niflumic acid, the RVD was largely blocked, and cell volume increased significantly by an additional 29.5% over that observed when hypotonic solution alone was applied (P Ͻ 0.05) (Fig.…”

“…In other cell systems, a primary role exists for volumeactivated outwardly rectifying Cl Ϫ channels in cell volume regulation (6,(22)(23)(24)36,(55)(56)(57)(58)(59). Thus, in response to swelling, Cl Ϫ channels mediate the net efflux of anions, which in turn promotes an RVD (60 -62).…”

Volume‐activated chloride channels in rat parotid acinar cells.

“…The currents induced by ionomycin had properties quite similar to those of other Ca2+-activated Cl-channels previously described in rat and sheep parotid acinar cells, lachrymal cells and human colon carcinoma cells (Iwatsuki et al 1985;Evans & Marty, 1986;Cliff & Frizzell, 1990;Ishikawa & Cook, 1993 (Kielland, 1937), the ordinate is the Cl-activity, not concentration. (Kubo & Okada, 1992;Lewis et al 1993;Stoddard et al 1993;Kelly et al 1994;Ackerman et al 1994). We examined the effect of 0-5 mm SITS on the volume-activated Cl-channels in parotid acinar cells.…”

Extracellular acidification elicits a chloride current that shares characteristics with ICl(swell)

“…The relative anion selectivity for the swelling-activated Cl Ϫ channel is SCN Ϫ Ͼ I Ϫ Ͼ Br Ϫ Ͼ Cl Ϫ Ͼ F Ϫ Ͼ gluconate; this sequence is referred to as "Eisenman sequence I" and indicates a weak interaction between the channel pore and the permeation anion. A number of different substances, including the stilbene derivative 4,4Ј-diisothiocyanostilbene-2,2Ј-disulfonic acid (DIDS) (9,35), the anti-inflammatory drug niflumic acid (20), the antiestrogen drug tamoxifen (43), diphenylamine-2-carboxylic acid (DPC) (22), and 1,9-dideoxyforskolin (DDFSK) (9), inhibit I Cl(swell) . Furthermore I Cl(swell) is insensitive to changes in calcium concentrations (33).…”