Changes in [Cl⁻]_i and mismatch between current and conductance, seen with double patch recording from MPN neurons and with “single patch” recording from cortical and hippocampal neurons. (A and B) Current, conductance, and ratio [Cl⁻]_o/[Cl⁻]_i from an MPN neuron recorded with two patch pipettes for direct measurement of V_m as well as current, during application of either 1.0 mM GABA (A) or 1.0 mM glycine (B). (C and D) Parameters as in A and B recorded (with a single patch pipette) upon application of 1.0 mM GABA to a pyramidal-shaped neuron from motor cortex, layer V (C), and a neuron from hippocampal area CA1–CA2 (D). Note the dramatic changes in [Cl⁻]_o/[Cl⁻]_i and the mismatch between current and conductance in A–D. Voltage ramp protocol and normalization as in Fig. 5. Gramicidin-perforated patch mode used in A–D.