Figure 2. Effect of pH on accumulation of naproxen by confluent SCC-25 monolayers. Cell monolayers were washed and overlaid with HBSS adjusted to the indicated pH. Kinetic analysis was performed as shown in Fig. 1, and the Vmax/Km ratio was used as an index of transport efficiency. The data are presented as the mean ± SEM of 5 experiments. Relative to pH 7.3, transport efficiency was significantly higher at pH 6.3 and 6.8 (P < 0.003, repeated-measures ANOVA), but similar at pH 7.8 and 8.3 (P > 0.3).