Fig. 6. ATP_e induces the efflux of anions but not cations from macrophages. Fluorescence microscopy of macrophages incubated for 10 minutes at 37°C in the absence (A and E) or in the presence (B-D and F-H) of 5 mM ATP. LY (A-D) or SR-B mM (E-H) was added at 37°C and cells were kept at this temperature until transferred to the stage of the microscope. In B and F, cells were loaded with the dye by incubation for 10 minutes in the presence of one of the dyes and ATP. In C and G cells were prepared as in B and F, respectively, washed, and kept in normal solution without the dye or ATP for an additional period of 10 minutes. In D and H cells were prepared as in B and F, respectively, washed, and kept in normal solution in the presence of 5 mM ATP and without the dye for an additional period of 10 minutes. In the LY experiments (A-D), macrophages were pre-incubated for 30 minutes and kept in the presence of probenecid (5 mM) during all incubations. Images in A-H is representative of the results of at least three independent experiments. Bar, 100 µm. (I) A quantitative comparison of the uptake of LY and SR-B by macrophages. Cells were incubated at 37°C with LY or SR-B for 10 minutes in the presence of 0, 1, 3 and 5 mM ATP and the amount of dye taken up by the cells was measured by spectrofluorimetry as described in the Materials and Methods. Data were normalized for a better comparison of the different data sets. Typical absolute values at 0 and 5 mM ATP were 1.2 and 28 mg of SR-B/mg protein and 0.2 and 1.0 mg of LY/mg protein. The bars represent the means of three independent experiments.