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We have a cultured method to grow rat mammry epithelial cells (RMEC) for 1 to 14 days in 1:1 mixture of Dulbecco´s Modified Eagle Medium: Nutrient and F-12 (DMEM/F-12) containing 10％ fetal bovine serum (FBS), human EGF, insulin, hydrocortisone, human transferrin adn 17β-estradiol in vitro. We were able to isolated and distinguish two cell types, luminal epithelial cells and myoepithelial cells, from primary clutures of RMEC. Immunocytochemical stains were used to distingusih liminal epithelial cells and myoepithelial cells. Peanut lectin (PNA) was stained in most alveolar epithelail cells and luminal epithelial cells of rats, while Thy-1.1, a maker of potential rat mammary myoepithelial cells, was expressed in myoepithelial cells in the rat. Also, we examined the expression patterns of three types of gap junction proteins, connexin 26 (Cx26), connexins 32 (Cx32) and connexin 43 (Cx43) by immunocytochemistry and western blot analysis. In the cell types, the results show that at the early stage of culture, luminal epithelial cells were increased and these cells were surrounded by myoepithelial cells. At the late stage of culture, luminal epithelial cells were decreased, in contrast myoepithelial cells were increased. In the expression pattem of gap junction, Cx26 maintained it´s expression until day 3, but afterwards gradually decreased in intensity. Expression of Cx32 remained until day 5, then decreased slightly. Cx43 gradually increased untill the middle time of culture then decreased in intensity. These results suggest that connexins may be important for the control of growth in rat mammary epithelial cell types.
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