Fig. 3. Voltage-dependence of CAATCH1 steady-state currents in the absence of free amino acid ligands. Net total currents measured in representative oocytes expressing WT or Y147F were obtained without amino acids in the presence of 100 mmol l^-1 Na⁺ (open squares), K⁺ (filled diamonds), Li⁺ (filled triangles) or NMG⁺ (open triangles). (A) Total WT currents (adapted from Feldman et al., 2000). (B) Net cation-specific WT-dependent currents obtained by subtracting the NMG⁺ currents in A at each voltage. (C) Total Y147F currents. (D) Net cation-specific Y147F-dependent currents obtained by subtracting the NMG⁺ currents in C at each voltage. V_m, membrane potential; I, current. The experiment was repeated 3 times.