Figure 2.

MCT7 mediates a bidirectional taurine transport.A and C, efflux of [³H]taurine by HEK293T cells expressing EGFP-tagged MCT7 (MCT7) or empty-vector (mock). [³H]taurine was loaded to the cells by incubation in NaCl buffer for 30 min. The cells were incubated in Na⁺-free buffer (pH 7.4) for designed time or in the pH-modified buffer (pH 6.5 or pH 8.5) for 30 min. The residual [³H]taurine in the cells was measured. B and D, [³H]taurine uptake (5 μM) was measured in Na⁺-free buffer (pH 7.4) for designed time or in the pH modified buffer (pH 6.5 or pH 8.5) for 30 min. E, concentration dependence of [³H]taurine uptake. The uptake was measured at designed concentration (1–270 mM). Velocity of MCT7-mediated uptake was calculated by subtracting the taurine uptake in mock-transfected cells from EGFP-tagged MCT7 transfected cells. F, intracellular and extracellular concentration of taurine in MCT7- or mock-transfected cells. The cells were incubated in Na⁺-free buffer (pH 7.4) for designed time. The residual taurine in the cells and effluxed taurine in the buffer were measured by LC-MS/MS. Each point represents the mean ± S.D. (n = 3). ∗∗ p < 0.01, compared with the corresponding mock-transfected cells by two-way ANOVA with Sidak's multiple comparisons test or one-way ANOVA with Tukey’s multiple comparison test. EGFP, enhanced green fluorescent protein; MCT7, monocarboxylate transporter 7.