Fig. 5. Uptake of anions but not cations occurs through a diffusion process. Fluorescence microscopy of cells incubated for 10 minutes at 37°C in the absence (A,D,F) or in the presence (B,C,E,G) of 5 mM ATP and cooled on ice in the absence of any dyes. Ethidium bromide (A,B), MQAE (D,E), or LY (F,G) was then added for 15 minutes and the cells were immediately transferred to the stage of the microscope. Temperature was kept all the time below 4°C. In C, cells treated as in B were heated up to 37°C and kept in the presence of ATP_e and ethidium bromide for 10 minutes. Experiments using MQAE were performed in a low chloride solution obtained by substituting Cl^– for glutamate in the normal extracellular solution. Each image is representative of the results of at least three independent experiments performed in duplicates. Bar, 100 µm.