Fig. 4.

Bidirectional transfer of ascorbate. Cells cultured on filters for 4 days were incubated for 1 h with ascorbate (∼330 μM) added to culture medium either above or below the cells and filter, as noted. Sulfinpyrazone (2 mM) was added as indicated above the cells at the beginning of the incubation. After the incubation, medium below the cells was sampled for assay of ascorbate that had crossed the membrane (B). Cells were rinsed 3 times in KRH and taken for assay of ascorbate (A). Concentrations of ascorbate above and below the cells measured at the end of these experiments were 0.35 ± 0.02 and 0.32 ± 0.02 mM, respectively. Results are shown from 6 experiments. *P < 0.05 compared with the sample not treated with sulfinpyrazone.