V-1-–null cells exhibit a defect in macropinocytosis. (A) Time course of intracellular accumulation of the nondigestible fluid phase pinocytic marker TRITC-dextran vs. time in WT cells (WT), V-1–null cells (V-1 Null), and V-1–null cells expressing FLAG-V-1 (V-1 Null + V-1) (see key). The values are the mean of duplicate samples. (B and C) Representative macropinocytic crowns in WT cells (B) and V-1–null cells (C) (arrowheads; the color coding indicates increasing distance from the coverslip). (D) The average number of macropincytic crowns per cell in WT and V-1–null cells. (Scale bar, 10 μm.) Mean and SD values are as follows: WT, 2.39 ± 1.80; V-1–null, 1.16 ± 0.80. ***P < 0.001.