Whole cell patch-clamp electrophysiology was performed on mature neurons (20–36 weeks old) derived from 6 CTL and 7 AD cell lines using previously described techniques (Lemtiri-Chlieh and Levine 2010). Neurons were selected for recording based on morphology, including pyramidal-shaped soma and presence of neurites. Artificial cerebrospinal fluid (aCSF) containing 125 mM NaCl, 2.5 mM KCl, 1.25 mM NaH2PO4, 1 mM MgCl2-6H2O, 25 mM NaHCO3, 2 mM CaCl2, and 25 mM dextrose was perfused through the recording chamber at 1–2 ml/min at room temperature. A high chloride internal recording solution was used containing 130 mM KCl, 10 mM HEPES, 10 mM phosphocreatine, 1 mM EGTA, 0.1 mM CaCl2, 1.5 mM MgCl2, 4 mM Na2-ATP, and 0.3 mM Na-GTP (pH 7.3), which allowed for GABA-evoked currents to be examined at a resting membrane potential of −70 mV. Upon break-in, patched cells were confirmed as neurons by the presence of voltage-gated sodium and potassium currents upon depolarizing voltage steps, ability of cells to fire an action potential upon depolarizing current injections, and noted for their resting membrane potential by injection with 0 current,
