Labeling with fluorescent carbocyanine dyes of cultured endothelial and smooth muscle cells by growth in dye-containing medium.

We describe a method for labeling cultured endothelial cells (ECs) and smooth muscle cells (SMCs) by letting the cells grow for three days in culture medium containing a low concentration of the fluorescent carbocyanine dyes DiI and DiO. We show that good labeling can be obtained with considerably lower concentrations (2.5 micrograms/ml) than has previously been described. With optimal concentration the labeling is very strong and seems to label all membranous structures in the cells. It was possible to clearly distinguish differentially pre-labeled cells both in coculture and seeded on denaturated vascular grafts. The cells remain fluorescent for more than seven days and may be passaged with retained proliferative capability. We suggest that DiI/DiO-labeling using dye-containing medium may be used for several cell types and is applicable in tissue culture and in the detection of implanted cells in vivo.