Fig. 4.

Increased cytosolic Na⁺ does not promote phosphate acquisition. Phosphate dose responses for parasite growth over 5 days in RPMI vs. 4:6 sucrose:KCl with 5% serum (circles and triangles, respectively; mean of 3 measurements each). In contrast to the prediction for Na⁺-coupled uptake, the phosphate EC₅₀ is not increased when erythrocyte Na⁺_i is reduced.