Biol. Pharm. Bull. 30(2) 247—253 (2007)

gestive heart failure since William Withering codified its use in 1785, the mechanisms of action of digitalis have been under extensive investigation for nearly 50 years, yielding one of the most specific mechanisms thus far defined for any agent so extensively used. Its ability to bind to and inhibit the Na-K-ATPase (NKA) has been well established, as has the resulting increase in cellular [Ca ] responsible for its positive inotropic action and its toxicity as well. However, recent observations suggest that digitalis has additional effects, such as the positive inotropic effect on heart muscle, and the inductive effect on cell growth, either hypertrophic on heart muscle cells or proliferative on vascular smooth muscle cells. The inductive effect of cell proliferation by nontoxic concentrations of digitalis has been observed by Christen and Dornand in studies on cell growth inducers for lymphocytes since 1975, and reports have published that ouabain exerts dual effects (proliferation and death) on cell growth at different concentration in different cell lines. Some researchers proposed the mechanism for ouabain’s proliferative inductive effect is its interaction with NKA; this interaction occurred at concentrations that did not induce enzyme activity inhibition and that transformed it into a signal transducer system. However, experimental evidence has been put forward showing that the effect of ouabain on cell survival and proliferation may be either independent of or dependent on the inhibition of cation transport. All of these data indicate that there maybe exist other target sites of digitalis in different cell lines besides NKA, and these target proteins play important roles in the regulation of cell growth and transformation with or without interaction with NKA. In this study we focused on the effect of low doses of ouabain on proliferation in endothelial cells and did the differential proteomic analysis of human umbilical vein endothelial cells (HUVEC) in response to low-dose ouabain. We compared the different protein expression of control cells and ouabain-treated cells and identified thirty-two proteins, in comparison with controls cells, the differential proteomic analysis of HUVEC treated by ouabain further revealed the variation of eight proteins regulated by ouabain treatment and expression of five of the protein spots increased and that of three proteins decreased. This new information gives new sights into the mechanisms for the proliferative effect of digitalis on HUVEC and provides potential avenues for the development of future therapeutic interventions for the treatment of cardiovascular diseases.