Effect of hRFVT-2 predicted and clinically relevant mutations on RF uptake by U87 cells. A) RF uptake by U87 cells stably expressing WT, L123 and its interacting residues (F119, L120 and L121). B) RF uptake by U87 cells stably expressing WT, L339 and its interacting residue (L342). 3H-RF (14 nM) uptake was performed in K-R buffer (pH 7.4) at 37°C for 3 min. Data are means ± SE of at least 4 independent experiments. *P < 0.01, **P < 0.05.