The ultrastructural localization of transient receptor potential C1 (TRPC1) channels in the sinus endothelial cells of rat spleen was examined by confocal laser scanning and electron microscopy. In addition, the localization of the closely associated proteins and channels, VE-cadherin, calreticulin, inositol-1,4,5-trisphosphate receptors type 1 (IP3R1), and ryanodine receptor (RyR), was also examined. Immunofluorescence microscopy of tissue cryosections revealed TRPC1 channels to be localized within the cytoplasm, in the superficial layer of the apical and basal parts of the cells, and in the junctional area of the adjacent endothelial cells. The distribution of Ca2+-storing tubulovesicular structures within endothelial cells was established by using tissue sections treated with osmium ferricyanide. Electron microscopy revealed densely stained tubulovesicular structures closely apposed to the plasma membrane and that occasionally ran closely parallel to the plasma membrane and near the caveolae and junctional apparatus. Immunolocalization analysis at the electron microscopy level using immunogold bound to the secondary antibody confirmed that TRPC1 channels were localized in the plasma membrane, caveolae, and vesicular structures in the subplasmalemmal cytoplasm of sinus endothelial cells. Calreticulin was predominantly localized in endoplasmic reticulum. IP3R1 and RyR, considered to be type 3, were colocalized in endoplasmic reticulum in proximity to the plasma membrane and caveolae. Thus, TRPC1 channels in sinus endothelial cells of the spleen might play an important role in controlling blood cell passage through phenomena including cytoskeletal reorganization, cell retraction, and disassembly of adherens junctions.