FIGURE 7.

Illustration of GAT-1 transport model (modified from Ref. 8). The C₆ and C₀ states represent the empty transporters with the binding sites facing the intracellular and extracellular sites, respectively. In NaCl buffer, the transporter binds the two ions sequentially, states C₁Na and C₂Na₂. The Na⁺-dependent transient currents are thought to be due to the partial reactions: C₆ ↔ C₀ ↔ C₁Na ↔ C₂Na₂. In LiCl buffer, the transporter binds one lithium ion (C₁Li) and membrane potentials more negative than −50 mV lead to opening of the conducting mode of the protein (C₁LiO). SKF89976A binding to the protein is described by the IC₅₀ values: in C₁Li (for the leak current), the SKF89976A IC₅₀ is higher than for the inhibition of the GABA-coupled current, whereas in C₂Na₂ (for the transient currents) the IC₅₀ is lower, as indicated by the arrows. The gray illustrations show the GABA transport modes of the transporter are not dealt with in this study and the Cl⁻ is omitted for clarity.