Clampex 10

Ionic currents were measured by using an OC-725C amplifier (Warner Instruments, Hamden, CT, United States) with a two-electrode voltage clamp. Generation of voltage-clamp protocols and data acquisition were performed using a Digidata 1550 interface (Molecular Devices, San Jose, CA, United States) controlled by Clampex 10.7 software (Molecular Devices). Data were sampled at 10 kHz and low-pass filtered at 1 kHz using Clampex 10.7 software (Molecular Devices). All experiments were performed at room temperature. A glass electrode with a resistance of 0.2–0.5 MΩ was prepared from a borosilicate glass capillary (GC150TF-10, Harvard Apparatus, Holliston, MA, United States) using a micropipette puller (P-1000, Sutter Instrument, Novato, CA, United States). The glass electrode was filled with 3 M KCl. ND66 solution (66 mM NaCl, 32 mM KCl, 1 mM MgCl₂, 1.8 mM CaCl₂, 5 mM HEPES, pH 7.6) was used as the extracellular solution (Decher et al., 2003 (link); Liu et al., 2020 (link)).

In field recordings, fEPSPs were recorded in the stratum radiatum of the hippocampal CA1 region using pipettes filled with ACSF. fEPSPs were amplified (MultiClamp 700B, Molecular Devices) and digitized (Digidata 1550, Molecular Devices) for measurements. The Schaffer collateral pathway was stimulated, and baseline responses were collected every 20 s with a stimulation intensity that yielded a half-maximal response. For input/output experiments, after acquiring a stable baseline, a series of increasing input stimuli were given to evoke output signals. Measured fEPSP slopes and fiber volleys were then interpolated by linear fits to plot input/output relationships. For paired-pulse ratio experiments, stimuli with indicated inter-pulse intervals (25, 50, 75, 100, 200, 300 ms) were given, pairs of peak amplitudes were recorded, and the ratio of that amplitudes was calculated. To induce LTP and long-term depression (LTD) at Schaffer collateral synapses on CA1 pyramidal neurons, high-frequency stimulation (100 Hz, 1 s), theta-burst stimulation (10 trains of 4 pulses at 100 Hz), or low-frequency stimulation (1 Hz, 15 min), was applied. Data were acquired by Clampex 10.2 (Molecular Devices) and analyzed by Clampfit 10 (Molecular Devices).

The two-electrode voltage clamp was performed with an Oocyte Clamp OC-725B (Warner Instruments, Hamden, CT, USA) that was controlled by Clampex 10.2 (Molecular Devices, Sunnyvale, CA, USA, www.moleculardevices.com). Intracellular glass microelectrodes, filled with 3 M KCl, had tip resistances in the 0.5–4 MΩ range. Agar bridges (3% agar in 3 M KCl) connected the bath electrodes to the experimental chamber. The holding potential applied (V_h) was −40 mV for all the experiments performed. The I-V curves of Fig. 1A were obtained applying 20 mV steps of 200 ms from −140 to +40 mV.
Oocytes were transferred in the recording chamber (Warner- RC-1Z) (warneronline.com) and impaled with microelectrodes; to recover from possible damage they were left for 2 min in a continuous solution flux. Only oocytes with resting potential equal or lower than −20 mV were used for the experiments. The number of discarded oocytes was not significantly different between treated and controls.
The capacitance and resistance values that were reported in Fig. 4 were obtained applying 10 mV steps of 20 ms every 200 ms in voltage clamp conditions. The protocol for the I-V curves of Fig. 1 was previously described^{52 (link)} and for Figs 5 and 7 is shown in Fig. 5A (10 mV steps of 750 ms from −80 to +40 mV).