Ouabain, a substance obtained from plant extracts, has been long known as cardiotonic, as well as by its high affinity to the Na-K- ATPase pump. The recent finding that ouabain is endogenously expressed in mammals has prompted research to determine its role as a hormone. We have shown that, in a physiological level (10 nM), it influences on three important features of epithelial physiology related to cell to cell contacts: (1) It modifies the Tight Junction integrity, as reflected by an increase in the Transepithelial Electrical Resistance (TER) of mature monolayers of MDCK cells. (2) It speeds up ciliogenesis, a feature closely related to epithelial (Apical/Basolateral) polarity and (3) It triggers Gap Junctional Intercellular Communication (GJIC). Since lack of GJIC has been associated to cancer, ouabain may be an interesting player on this issue.Sociedad Argentina de Fisiología