Figure 6.

The pH-dependent uptake of [³H]histidine, [³H]carnosine, [³H]Gly-Sar, and [³H]valacyclovir in stably transfected COS-7/Mock and COS-7/hPHT1 cells. Cells were seeded at a density of 5 × 10⁴ cells/cm² in 24 well, tissue culture treated plates. Uptake experiments were performed 2 days post-transfection for 10 minutes at pH 5 and 7.4. The reaction was stopped using ice-cold phosphate buffered saline, after which the cells were lysed. Radioactivity in the cell lysate was measured by liquid scintillation counting. Final scintillation counts were normalized to total protein. * p ≤ 0.05, ** p ≤ 0.01, and *** p ≤ 0.001.