Overexpression of α6β3δ subunits results in large tonic GABA current in cultured hippocampal neurons. A, Typical recordings showing whole-cell currents induced by rapid application of GABA (20 μM) in GFP control and α6β3δ-transfected neurons in the presence of TTX (1 μM) and DNQX (10 μM). B, Summarized data showing no significant difference in whole-cell GABA currents between the two groups. C, Typical traces of tonic GABA currents, revealed by application of Bic (40 μM) in the presence of TTX (1 μM) and DNQX (10 μM), recorded from a GFP control neuron and a α6β3δ-transfected neuron. Holding potential = −70 mV. D, Summarized data showing that the average amplitude of tonic GABA currents was significantly increased in α6β3δ-transfected neurons (28.1 ± 3.6 pA, n = 10), compared to the GFP controls (7.4 ± 1.1 pA, n = 11; ***, p < 0.0001). E, Tonic currents activated by THIP (5 μM) in GFP control and α6β3δ-transfected neurons. F, Summarized data showing a significant increase of THIP-induced tonic currents after transfection of α6β3δ subunits (962 ± 130 pA, n = 12), compared to the GFP controls (35.3 ± 7.4 pA, n = 11; ***, p < 0.0001).