Fig. 3.

Tonic conductance was not affected by GABA alone but was increased by GABA plus depolarization. A: average GABA- and depolarization-induced changes in E_GABA determined from 8 neurons. As in Fig. 2, E_GABA was measured after 2 and 10 s of GABA application. Depol., depolarization. B: tonic conductance before and after GABA application. Tonic conductance was calculated using measurements of tonic current from experiments as in Fig. 1 and mean values for E_GABA (see materials and methods). GABA alone did not significantly affect tonic conductance. GABA plus depolarization produced an increase in tonic conductance. C: comparison of observed shifts in E_GABA (delta E_GABA) with theoretical shifts that would be required to produce the observed tonic current changes, assuming no change in tonic conductance (i.e., assuming tonic current change was solely due to driving force alterations from shifts in E_GABA). With GABA application alone, there was no difference between the observed shift in E_GABA and the theoretical value, indicating that tonic current reduction by GABA was caused by reduced driving force. With GABA plus depolarization, the theoretical E_GABA shift was significantly larger than experimental observation, indicating that depolarization increased tonic conductance independently of driving force changes. n.s., Not significant. **P < 0.01; ***P < 0.001.