An elevated blood level of homocysteine (Hcy) is an independent risk factor for cardiovascular disease, but it is unclear how Hcy affects blood vessels. The canonical transient receptor potential channels (TRPC) are Ca2+-permeable cationic channels that we have shown to have a novel redox-related mechanism with relevance to inflammation (Xu et al., 2008a). In this study we examined the potential contribution of TRPC in homocysteine-induced endothelial dysfunction. Human umbilical vein endothelial cells (HUVECs) were used according to the guideline of local ethic approval. Primary cultures of HUVECs were grown in endothelial growth medium (PromoCell, Germany), and the cell passage number less than 5 was used for experiments. TRPC-transfected HEK-293 cells were grown in DMEM-F12 (Invitrogen, UK) medium containing 10% fetal calf serum. Cells were maintained at 37°C under 95% air and 5% CO2. Cells were seeded onto 48-well or 96-well cell culture plates and cell proliferation assayed using WST-1 kit (Roche) (Xu et al., 2008b). Data are expressed as mean ± S.E.M. The unpaired student’s t test or ANOVA was used where appropriate. All experiments were reproducible from at least three independent experiments. Hcy at concentrations of 0.05-5 µM increased the proliferation of HUVECs, but high concentration (50 µM) decreased the proliferation, suggesting that the function of endothelial cells was regulated by the concentrations of Hcy corresponding to the modest increase in the circulating Hcy. To test the involvement of TRPC channels, we firstly examine the effect of Hcy on cell proliferation using TRPC-transfected HEK-293 cells. Using the culture medium without L-cysteine and L- methionine, Hcy (0.5-50 µM) significantly increased the proliferation of TRPC5-transfected cells in a dose dependent manner. The absorbance was increased by 2.52 ± 0.05 fold (n = 16, P<0.001) at 50 µM Hcy, while no effect was observed for the non-transfected cells. This stimulating effect on cell proliferation was related to channel activation. Secondly, we found the inhibition of TRPC4, TRPC5 and TRPC6 by the application of functional TRPC blocking antibodies resulted in the inhibition of proliferation in HUVECs. In addition, we found that the antioxidants (vitamin E and Se2+) displayed protective effects against Hcy-evoked cell proliferation. These data indicate a new role of TRPC channels in the vascular endothelial cell pathophysiology, which should have an important significance for the understanding of Hcy-related disease processes.