Two-electrode voltage-clamp technique

Two to four d after injection, the oocytes expressing the wild-type GABA_A receptors were placed in a custom-made small volume chamber with continuous perfusion with oocyte Ringer's solution (OR2), which consisted of (in mmol/L) 92.5 NaCl, 2.5 KCl, 1 CaCl₂, 1 MgCl₂, and 5 HEPES, at pH 7.5. The chamber was grounded through an agar KCl bridge to prevent any ligand-induced junction potential change. The oocytes were voltage-clamped at −70 mV to measure GABA-induced currents using an AxoClamp 900A amplifier (Molecular Devices, Sunnyvale, CA, USA). The current signal was filtered at 50 Hz with the built-in 4-pole low-pass Bessel filter in the AxoClamp 900A and digitized at 100 Hz with the Digidata1440A digitizer (Molecular Devices) and pClamp10.