Figure 2.

Currents evoked by GABA and glycine. (A) Currents evoked by GABA (top) and by glycine (middle) in concentrations as indicated, at a V_m of −8 mV. (Different cells used for top and middle). (Bottom) Concentration–response curves for currents evoked by GABA and glycine. Symbols show peak currents (mean ± SEM; n = 4–6) recorded at −8 or 0 mV and normalized to the maximal response in each neuron. Smooth lines are described by Eq. 2 fitted to the experimental data. The Hill slopes were 1.5 and 1.8 for GABA and glycine (Gly), respectively, and SEM of ln(EC₅₀) were 0.090 and 0.054. (B) Apparent cross-desensitization of GABA- and glycine-evoked currents, recorded when GABA or glycine was added 20 s after the start of perfusion with the other agonist. Left and right panels are from the same cell. Note that the responses to the second (within each pair) application are reduced compared with the responses to the same agonist applied first. Note also that apparent cross-desensitization was observed with standard solutions (see Materials and methods) when GABA- and glycine-evoked currents were of roughly similar magnitude (top, V_m of −8 mV) as well as when glycine-evoked currents were considerably smaller than GABA-evoked currents (middle, V_m of 0 mV), and that apparent cross-desensitization was also observed with nearly symmetrical Cl⁻ concentrations (see Materials and methods) resulting in inward currents at −40 mV (bottom). Interval between pairs (left and right columns) was 140 s (top), 120 s (middle), and 84 s (bottom). (For some cells, recordings at −8 mV were preferred over those at 0 mV because of substantially lower background noise.) Amphotericin-perforated patch mode (A and B).