Figure 2.

Voltage-dependent increases in tonic conductance were insensitive to inhibition of transporter-mediated or vesicular GABA release. A: Current responses to bicuculline application (Bic, 10 µM) under control conditions (left panel) and in the presence of SKF89976A (SKF, 40 µM) (right panel). Tonic current was increased by SKF. Holding potential was −40 mV. B: Mean tonic current density (pA/pF) vs. voltage under control conditions and in presence of SKF (n=6). Outward rectification was unaffected by SKF. C: Mean capacitance-specific conductance vs. voltage (n=6). There was a shift in the conductance curve, but the voltage-dependence of tonic conductance was unaffected by SKF, the slopes of the solid lines are 0.31 pS/pF*mV⁻¹ and 0.33 pS/pF*mV⁻¹ for control and SKF, respectively. Symbols are same as panel B. D: Current responses to Bic under control conditions (left panel) and with zero extracellular Ca²⁺/1 mM EGTA (right panel). As seen previously (Wu et al., 2006), phasic currents were reduced by zero extracellular Ca²⁺ but tonic currents were not (amplitudes of illustrated tonic currents were −31 pA for control and −38 pA for zero Ca²⁺). Holding potential was −60 mV. E: Tonic current density vs. voltage for experiments with zero Ca²⁺/1 mM EGTA (n=6). F: Capacitance-specific conductance vs. voltage for all neurons tested in zero Ca²⁺/1 mM EGTA. Same symbols as E. The voltage-dependent increase in tonic conductance was independent of extracellular Ca²⁺. Slopes of the solid lines are 0.30 pS/pF*mV⁻¹ and 0.23 pS/pF*mV⁻¹ for control and zero Ca²⁺, respectively.