Distinct voltage‐dependent gating behaviours of a swelling‐activated chloride current in human epithelial cells.

Abstract

1. The swelling-activated chloride current is critical in the homeostatic regulatory volume decrease (RVD) of both excitable and non-excitable cells. Although not activated by voltage, it displays kinetic behaviour similar to voltage-gated Shaker-type potassium currents. We have studied the voltage-dependent properties of this current in single T84 human cell line epithelial cells using whole-cell patch clamp methodology. 2. An external anion permeability sequence of I-> Cl-> methanesulphonate (MeSO3) was observed for the swelling-activated current. Extracellular application of the chloride channel blocker DIDS (100/,M) resulted in -50 % block of the current in a voltage-dependent manner. 3. At positive membrane potentials, the swelling-activated chloride current undergoes timedependent inactivation. Following such inactivation, recovery of both the inward and outward components of the macroscopic current was found to be voltage dependent. The time constants describing these two individual recovery processes were identical over a range of membrane potentials. In addition, the magnitude of current recovery was directly dependent upon the degree of prior inactivation of current at positive voltage. 4. We further observed that the swelling-activated current undergoes a form of steady-state, voltage-dependent inactivation that appears to differ from the inactivation observed at positive potentials. This steady-state inactivation occurred over the physiological voltage range, with a membrane potential at half-maximal inactivation (V½) of -72 mV, and differed from the time-dependent inactivation observed at positive membrane potentials, which occurred with a V½ of 40 mV. These observations demonstrate two distinct forms of voltagedependent inactivation, probably reflecting two separate gating processes at the level of the channel. 5. These latter properties are thus anticipated to regulate voltage-dependent chloride efflux under cell swelling conditions and further influence RVD and membrane excitability in cells generating action potentials.

Small‐conductance Cl– channels contribute to volume regulation and phagocytosis in microglia

“…Biophysical differences include lack of inactivation and a smaller single‐channel conductance. Most I Clswell exhibit voltage‐sensitive inactivation (Jackson & Strange, 1995a; Nilius et al ., 2003), although the rate and degree vary (Jentsch et al ., 2002), and may depend on extracellular Mg 2+ (Braun & Schulman, 1996; Voets et al ., 1997). Microglia lack inactivation, even at strongly depolarized potentials, and with the highest divalent cation concentration used in previous I Clswell studies.…”

“…;3 Eder et al (1998);4 Jackson et al (1995b); 5Boese et al (1996); 6 Jentsch et al (2002); 7 d'Anglemont de Tassigny et al (2003); 8 Nilius et al (2003); 9 Sardini et al (2003); 10 Lewis et al (1993); 11Schumacher et al (1995);12 Nilius et al (1998);13 Braun et al (1996); 14Voets et al (1997);15 Meyer et al (1996);16 Wang et al (2005). *The negative sign ()0.10) indicates an increase in volume.…”

External anions and volume-sensitive anion current in guinea-pig ventricular myocytes

“…The estimated values relative to Clwere 1.21 ± 0.09 for iodide, and 0.43 ± 0.07 for aspartate. The estimate for iodide is in good agreement with relative values determined in recent studies on human epithelial cells (1.37, Braun and Schulman 1996) and guinea-pig atrial and ventricular cells (~1.1, calculated from data in Fig. 2 of Duan et al 1999), whereas the estimate for aspartate is similar to the 0.45 value reported for anion current carried by ClC-3 channels expressed in NIH/3T3 cells (Duan et al 1997).…”

“…Clcurrent through this outwardly-rectifying channel (I Cl,Vol ) inactivates during depolarizations to high positive potentials (Duan et al 1997;Duan et al 1999), a property that has been described for I Cl,Vol in a wide variety of cell types, in-cluding T lymphocytes (Lewis et al 1993), epithelium (Worrell et al 1989;Kubo and Okada 1992;Braun and Schulman 1996), endothelium (Nilius et al 1994), osteoblast-like cells (Gosling et al 1995), and various cancer-cell lines (Anderson et al 1995).…”

Biophysical and pharmacological characterization of hypotonically activated chloride currents in cortical astrocytes

“…Of note is that NPPB and niflumic acid appeared to produce a voltage-independent block of both outward and inward currents, whereas DIDS appeared to produce predominantly a voltage-dependent block of outward currents only. Such a voltage-dependent block by DIDS has been demonstrated previously for swelling-activated chloride currents in other cell types (Braun and Schulman, 1996;Ehring et al, 1994;Winpenny et al, 1996;Mitchell et al, 1997). We compared the percentage inhibition by each test drug in Figure 4D,E.…”