Fig. 3.

Effects of GABA on Ca²⁺current. A, A family of superimposed Ca²⁺ currents elicited from a type B cell at a holding potential of −30 mV. A1, Control; A2, after the application of 10 nm GABA;A3, after the application of GABA (30 μm). B, Current–voltage plot of control and GABA-induced effects on the Ca²⁺current. Graph was generated from current traces shown inA1–A3. From a holding potential of −30 mV, the sHVA Ca²⁺ current was the predominant Ca²⁺ current activated by the command steps. A low concentration of GABA (10 nm) enhanced the current. Higher concentrations of GABA (30 μm) reduced the sHVA Ca²⁺ current. C, Dose–response curve was generated using the same equation as described in Figure 1D. The half-activation concentration for GABA at low concentrations as estimated from four experimental data points with a logistic function was 12.5 nm using a power of 1.5 as the best fit. I_max was equal to the current recorded at the saturation concentration of GABA between 500 and 1000 nm. For each cell, a profile of the effect of GABA from a lower to higher concentration was plotted as the example shown in Figure 4E. I_maxwas the peak of the profile of the biphasic concentration curve.I_min is the current measured before GABA application. D, At low concentrations, GABA enhanced the tLVA Ca²⁺ current (see A). Traces from a type A cell were generated from a holding potential of −80 mV to a step depolarization of −10 mV. The trace in a is in the presence of 10 nm GABA, and the trace inb is the control. The difference current (dotted line) corresponds to the increase in the tLVA Ca²⁺ current attributable to GABA.