The extracellular solution contained 2.5 mM glucose, 140 mM NaCl, 5 mM KCl, 2.6 mM CaCl2, 1.2 mM MgCl2 10 mM HEPES (pH 7.4 adjusted with NaOH, osmolarity 295 mOsm/L adjusted with sucrose). The intracellular solution was 120 mM KCl, 1 mM CaCl2, 1 mM MgCl2, 10 mM EGTA, 10 mM HEPES (pH 7.2 adjusted with KOH, osmolarity 285 mOsm/L adjusted with sucrose)39 (link).
Cells were plated on 13 mm cover slips and patched at a holding potential of − 60 mV. Voltage steps were applied from − 100 to + 30 mV in 10 mV steps, each lasting 500 ms, with 100 ms between. The sampling rate was set to 20 kHz and filtered using a 4-pole Bessel filter at 4 kHz. Currents were recorded from individual cells and scaled by their estimated whole cell capacitance following whole cell compensation.