Effects of LPS on macrophage fluid phase uptake in the presence of (A) 1 μmol/L SB203580 or (B) 2 μmol/L PD098059. Murine clone 4-4 macrophages were preincubated with the inhibitors for 1 hour and stimulated with LPS for 45 minutes at 37°C in the presence of [³H]sucrose and the appropriate inhibitor. Subsequently, the cells were placed on ice and washed, and accumulated radioactivity was determined by scintillation counting. Using the specific activity of the [³H]sucrose, fluid phase uptake was expressed as femtoliter per cells per minute. The results show the average of three independent determinations.