FIGURE 5. Concentration-dependent inhibition of adenosine and adenine uptake.

(A, B) Competitive inhibition of 150 nM [³H]adenosine uptake for 60 min into oocytes expressing PfENT4 (black circles), PvENT4 (gray triangles), or H₂O-injected oocytes (white squares) with increasing concentrations of unlabeled adenosine. The data for ENT4-expressing oocytes are fit with a single-site competition curve. (C, D) Competitive inhibition of 150 nM [³H]adenine uptake for 60 min into oocytes expressing PfENT4 (black circles), PvENT4 (gray triangles), or H₂O-injected oocytes with increasing concentrations of unlabeled adenine. The data for ENT4-expressing oocytes are fit with a two-site competition curve. Panels (A) and (C) show the raw uptake values and panels (B) and (D) show the background-subtracted uptake into oocytes expressing PfENT4 and PvENT4 normalized to a % of uptake in the absence of unlabeled competitor. In these experiments, 8 oocytes were pooled together into one vial for scintillation counting, and each point is the amount of radioactivity detected divided by 8. The results from one representative experiment are shown.