CLC-0 (Jentsch et al. 1990 ) and human CLC-1 (Koch et al. 1992 ) were expressed in Xenopus oocytes and currents were measured at 18°C 2–5 d after injection using the inside-out configuration of the patch-clamp technique (Hamill et al. 1981 ) with an EPC-7 amplifier (List) and the acquisition program Pulse (HEKA). Pipettes were pulled from aluminosilicate glass capillaries and had resistances of 1–4 MΩ. Pipettes were coated with Sylgard (Corning Inc.) and fire polished. Data were sampled at 20 or 100 kHz (depending on pulse durations) and filtered at 5 or 10 kHz, respectively, with an eight-pole low-pass Bessel filter. Data analysis was performed using self-written software (Visual C++; Microsoft Corp.) and the SigmaPlot program (Jandel Scientific).
Standard bath (internal) solution contained (mM): 120 NMDG-Cl, 2 MgCl2, 10 HEPES, and 2 EGTA, pH 7.3, while standard extracellular (pipette) solution contained (mM): 100 NMDG-Cl, 5 MgCl2, 10 HEPES, and 2 EGTA, pH 7.3. In the low external chloride solution, 90 mM of NMDG-Cl was replaced with 90 mM of NMDG-glutamate. pH was adjusted with NMDG or HCl to the desired value. Mutant I290M is described inPusch et al. 1995b . RNA synthesis and oocyte injection were performed as described (Wollnik et al. 1997 ; Saviane et al. 1999 ).
Standard bath (internal) solution contained (mM): 120 NMDG-Cl, 2 MgCl2, 10 HEPES, and 2 EGTA, pH 7.3, while standard extracellular (pipette) solution contained (mM): 100 NMDG-Cl, 5 MgCl2, 10 HEPES, and 2 EGTA, pH 7.3. In the low external chloride solution, 90 mM of NMDG-Cl was replaced with 90 mM of NMDG-glutamate. pH was adjusted with NMDG or HCl to the desired value. Mutant I290M is described in
