Nucleotide microinjection experiments.

Human HS-68 fibroblasts were grown on coverslips. Nucleotide triphosphates were microinjected at an estimated final concentration of 500 μmo/L. To identify the microinjected cells, fluorescein isothiocyanate-labeled dextran was co-injected with the nucleotides; therefore, the microinjected cells appear in green (C, E). Cells were incubated with 150 nmol/L MT orange (red stain) for 30 minutes to stain for mitochondria membranes, and fixed in 4% paraformaldehyde, and DNA was dyed with DAPI stain (blue, A, C, E). Left panels represent composite pictures that include DNA (blue), mitochondria (red), and dextran (green for microinjected cells). Right panels (B, D, F) represent the stained mitochondria alone. Cells treated with 2CdATP show a rearrangement of the mitochondria. Cells treated with the same concentration of F-AraATP do not display the same morphologic changes. Images were obtained with a Zeiss Axioscope microscope, equipped with CCD camera, using a 40 × 1.3-na oil objective.