After formation of GΩ-resistance seals, whole-cell configuration was established, and currents were measured at a holding potential of −60 mV, using an Axopatch 200B amplifier (Molecular Devices, Union City, CA). Current-voltage ramp relations
were recorded using voltage ramps from −100 to +100 mV with a duratron of 0.8 s. Data were collected and analyzed with the pClamp 9.0 software. Measurements were performed at room temperature (~22°C).