Figure 7.
GABA triggers an optical signal only when membrane potential is depolarized. A1, Averaged optical traces after application of GABA (30 μm, 30 s) on patched neurons (n = 6) at −60 mV (full line) or at 0 mV (dotted line). Note that GABA triggers an optical response only when the membrane potential was depolarized. A2, Same application of GABA on nonpatched neurons (n = 7) from the same culture. In these conditions, GABA did not elicit an optical signal. Calibration: 1 min and 2°. B, Coupled and averaged recordings of phase (full line) and Vm (dotted line) obtained after application of GABA (30 μm, 30 s, arrowhead) show a hyperpolarization of membrane potential triggered by GABA, which is not associated with detectable phase-shift changes (n = 7). Calibration: 1 min, 2°, and 2 mV. C, Averaged optical traces obtained after the successive application of GABA (1–100 μm, 30 s; arrowhead) to the same unpatched cells (n = 8). No optical response was observed in these conditions.