Figure 7.

hENT4-mediated efflux of [³H]2-chloroadenosine. (a) PK15-hENT4 cells were incubated with 30 μM [³H]2-chloroadenosine and 50 nM ABT-702 for 12 min in pH 6.0 transport buffer. Cells were washed in ice-cold buffer to remove extracellular substrate, and then efflux was initiated by adding transport buffer at the indicated pH. Aliquots of extracellular solution were taken at the specified times and assessed for [³H]content. Data were fitted by a one-phase association curve. Each point represents the mean ± S.E.M. from 5 independent experiments. *Significant difference between efflux at pH 6.0 and 7.5 or 8.2. # Significant difference between pH 6.0 and 7.5 (Two-way ANOVA with Tukey’s multiple comparisons test, P < 0.05). (b) Inhibition of efflux by D22 and TC-T6000. [³H]2-chloroadenosine efflux was measured at pH 6.0, as described for Panel a, in the presence of D22 (2 μM) or TC-T6000 (1 μM). Each bar represents the mean ± S.E.M. from 5 experiments. The dashed line represents the uptake at pH 7.5 (from Panel a), shown for comparison. *Significant difference from efflux at pH 6.0 in the absence of inhibitor (Two way ANOVA with Tukey’s multiple comparisons test, P < 0.05).