Single-channel data were acquired using Axopatch 200B or 700B amplifiers (Molecular Devices, Sunnyvale, CA, USA) interfaced via a Digidata 1440 to a PC running pClamp suite software (Molecular Devices). When signals were acquired with an Axopatch 200B amplifier, currents were filtered with an 8-pole, low pass Bessel filter LPF-8 (Warner Inst., Hamden, CT) at 0.2 kHz. The pipette was pulled with a horizontal puller (Sutter P-97; Sutter Inst., Novato, CA). The resistance of the pipette in the corresponding bath medium was 7–12 MΩ. Typical bath solution was (in mM): 150 NaCl, 1 CaCl2, 2 MgCl2, 10 HEPES (pH 7.4). Pipette solution for the cell-attached configuration was (in mM): 140 LiCl, 2 MgCl2 and 10 HEPES (pH 7.4). Gap-free single channel current data from gigaohm seals in principal cells were acquired and subsequently analyzed with Clampfit 10.2 software (Molecular Devices). NPo, the product of the number of channels (N) and the open probability (Po), was used to measure the channel activity within a patch. Single-channel unitary current (i) was determined from the best-fit Gaussian distribution of amplitude histograms. Channel activity was analyzed as NPo = I/i, where I is mean total current in a patch and i is the unitary current at this voltage. Where appropriate, Po was calculated by normalizing NPo for the total number of estimated channels in the patch.