FIGURE 11.

Na⁺ affinity for LeuT is pH-dependent and is modulated by K⁺ ions. Na⁺-dependent [3H]leucine binding to purified LeuT in DDM was assessed with scintillation proximity assay. At pH 8 (blue curves), the IC₅₀ for Na⁺ was significantly (p < 0.0001) reduced when ChCl (800 mm, filled squares) was substituted with KCl (800 mm, open squares). The IC₅₀ value of Na⁺ was not significantly different at pH 6 (red curves) between ChCl and KCl substitution but increases significantly (p = 0.0005) in ChCl when pH is changed from 8 to 6 (Table 1). The data are means ± S.E. (error bars) of four or five individual experiments performed in triplicate. Statistical analysis performed with one-way analysis of variance with Tukey's multiple comparison test (F value: 43.7, p < 0.0001).