(a)Microtubules (b)Microfilaments Figure 22-1 The Intracellular Distribution of Microtubules Microfilaments, and Intermediate Filaments. (a) The distribution of microtubules in cells of the kangaroo rat kidney cell line(PtK-1l visualized by immunofluorescence staining for tubulin For reference, the ucleus has been stained with the red fluorescent DNA stain propidi odide. (b) The distribution of microfilaments in a rat kidney cell line visualized by staining actin with a fluorescent derivative of phalloidin (c) The distribution of intermediate filaments in PtK-1 cells, visualized by immunofluorescence staining for keratin. Here the nucleus has also been (c)Intermediate filaments 5um stained with propidium iodide