Figure 5.

(A) Kinetic model for glutamate transport by EAAC1. Glutamate binding to the empty transporter, T, leads to the formation of the glutamate-bound state, TL. T′ and T′L are the respective states with the substrate binding site exposed to the cytoplasm. Charge translocation is assumed to be quasi-irreversible (zero-trans conditions). Na⁺ and K⁺ binding steps were assumed to be in rapid pre-equilibrium. (B) Simulation of steady-state anion and transport currents (Eqs. 3 and 4, Appendix). The following parameters were used: K_d = 50 μM, k_f⁰ = 300 s⁻¹, k_b⁰ = 40 s⁻¹, Φ₁ = 20, Φ₂ = 0.5, γ = 4 fS, z = −2, δ = 0.8. The conditions of the simulation were chosen similar to the experiments shown in Fig. 4 D and E. (C) Simulation of voltage-dependent currents as a function of time by numerical integration of the rate equations pertaining to the mechanism in A (conditions as in Fig. 4A). The rate constants for glutamate binding and dissociation were set to 2⋅10⁷ M⁻¹⋅s⁻¹ and 1000 s⁻¹, and k_op and k_cl were set to 1400 s⁻¹ and 700 s⁻¹, respectively. The other parameters were identical to those in B.