FIGURE 5.

Voltage jump-induced pre-steady-state currents. (A) Difference between whole-cell current recordings obtained from one HEK293 cell with +90 and −90 mV voltage jumps in the absence and presence of SKF-89976A. The charge moved in this process was 778 and −259 fC, respectively. The solid lines represent the exponential time course of the currents. The inset represents the correspondent voltage protocol. (B) Voltage dependence of the moved charge in response to a voltage jump, Q(V_m), normalized to I_ss evoked by 200 μM GABA (n = 3 cells, values are means ± SE). The solid line was calculated according to a Boltzmann equation (see Materials and Methods) with V_Q = −9.9 mV and z_Q = 0.94, Q₁ = −24 fC/pA and Q₂ = 54 fC/pA. (C) Normalized maximum charge movement associated with voltage (Q_Vm) or GABA concentration (Q_τ2 and Q_τ3) jumps. Q_Vm was calculated by subtraction of the extreme points of the Boltzmann relationship, Q₁ and Q₂. For the GABA concentration jumps maximum charge movement was estimated at saturating GABA concentrations. The experiments in A and B were performed with external 60 mM NaCl (Na⁺ substituted with TMA) and with KAsp as internal solution.