1550b digitizer

Micropipettes were fabricated from quartz glass capillaries (QF100-50–7.5, Sutter Instrument, Novato, CA) using a P-2000 micropipette laser puller (World Precision Instruments, Sarasota, FL). An Ag/AgCl wire was inserted in the micropipette to act as the working electrode and another Ag/AgCl wire was immersed in a 1 × PBS bath (Oxoid Ltd, Thermo Fisher, UK), acting as the reference electrode. Current–voltage measurements are performed using a MultiClamp 700B patch-clamp amplifier (Molecular Devices, Sunnyvale, CA). The signal was filtered using a Digidata 1550B digitizer, with a low-pass filter at 10 kHz, and signal recording was performed using the pClamp 10 software (Molecular Devices), at a rate of 100 kHz. For electrochemical analysis experiments, the micropipettes were filled with 1 × PBS. For electrowetting experiments, the micropipettes were filled with a solution of 10 mM tetrahexylammonium tetrakis(4-chlorophenyl)borate (THATPBCl) salt in 1,2-dichloroethane (1,2-DCE).

Whole-cell sodium currents were recorded at room temperature from HEK 293 cells 48 h after transfection using an Axopatch 200A amplifier, a Digidata 1550B digitizer, and the pClamp 10.6 software (Molecular Devices, San Jose, CA, USA). Current signals were filtered at 5 kHz and sampled at 10 kHz. Patch-clamp pipettes were pulled from borosilicate glass using a vertical puller (Narishige, London, UK) to a resistance of 3–4 MΩ. The internal solution contained (in mM): NaCl 10, CsF 120, CsCl 10, EGTA/CsOH 5, HEPES 5 (pH 7.2 with CsOH). The external solution contained (in mM): NaCl 150, KCl 4, CaCl₂ 2, MgCl₂ 1, glucose 5, HEPES 5 (pH 7.4 with NaOH) [43 (link)]. Detailed protocols are described in Supplementary Materials and Methods.