Intracellular Ca2+ signaling controls many cellular functions. Understanding its regulation by selenoproteins is essential for understanding the role of selenoproteins in regulating cell functions. The activity of thioredoxin reductase (TrxR), thioredoxin (Trx) content, and the activity of glutathione peroxidase (GPx) in the human endothelial cells cultured in selenium-supplemented medium (refer as Se+ cells) was found 70%, 40%, and 20% higher, respectively than those in the cells cultured in normal medium (refer as Se0 cells). The intracellular Ca2+ signaling initiated by inositol 1,4,5-trisphosphate (IP3), histamine, thapsigargin (TG), carbonyl cyanide p-(tri-fluoromethoxy) phenyl-hydrazone (FCCP), and cyclosporin A (CsA) was investigated in both Se+ and Se0 cells. It was interestingly found that the higher activity of selenoproteins reduced the sensitivity of IP3 receptor to the IP3-triggered Ca2+ release from intracellular stores, but enhanced activation of the receptor-coupled phospholipase C in histamine-stimulated Se+ cells by showing much more generation of IP3 and higher elevation of cytosolic Ca2+. The higher selenoprotein activity also reduced susceptibility of the uniporter to the mitochondrial uncoupler, susceptibility of the permeability transition pore (PTP) to its inhibitor, and the vulnerability of endoplasmic reticulum (ER) Ca2+-ATPase to its inhibitor in selenium-supplementing cells. The results suggest that cell calcium signaling is subjected to thiol-redox regulation by selenoproteins.