PAS staining and electron microscopic analysis of vascular channels formed by MDA-MB-231 cells. (a) PAS staining was performed on MDA-MB-231 cells plated on matrigel for 24 hours to identify the extracellular matrix secreted by cells. Pink staining refers to the glycogen and related mucopolysaccharides secreted by the cells to form the extracellular matrix-rich vascular channels. (b) Transmission electron microscopic analysis was performed on MDA-MB-231 cells plated on matrigel for 24 hours. A cluster of cells came into contact with each other to form vascular channels. There was cytoplasmic ruffling and protrusion at cell contact position. (c) There was evidence of stretching of cellular contents to form the tubular channel-like structure. (d) Absence of tight junctions between adjacent cells involved in vascular channel formation was observed. PAS, periodic acid-Schiff.