Our biochemical and Tulathromycin B proteomic analysis of the platelet proteins associated with the C-terminus of SERT demonstrate an association between vimentin, an intermediate filament, and SERT in platelets. Association also was noted in a CHO heterologous expression system. Vimentin is the major type III intermediate filament expressed in cells of mesenchymal and myogenic origin. Vimentin, a minor component of the platelet cytoskeleton, is associated with the Triton X-100 insoluble Chloroquine Phosphate fraction of human platelets. Studies have shown that vimentin forms a network of intermediate filaments that form a ring close to the cell membrane, as well as a network that activates PAK-dependent phosphorylation of vimentin, altering the filamentous structure of this cytoskeletal compound. Our studies demonstrate an association between vimentin and SERT in the cytosol and on the plasma membrane of platelet and CHO-expression system within 5HTindependent manner. Collectively, these findings point to vimentin as a possible candidate for facilitating the translocation of SERT between intracellular compartments and plasma membrane. When 5HT-stimulation dependent phosphorylation was eliminated, the surface expression and the 5HT uptake rates of SERT were restored in CHO cells treated with 100 mM 5HT. Of the several C-terminus mutant transporters, only D14 and S611D did not associate with vimentin although both could appear on the plasma membrane in active form. Additionally, neither the plasma membrane expressions of these two mutant transporters were decreased in 100 mM 5HT-treated cells, nor they were able to bind phosphovimentin. These data strengthen our hypothesis that the modification of the SITPET sequence differentially, one amino acid at a time, exposes the vimentin binding domain on the Cterminus of SERT. However, elevated plasma 5HT controls the cellular distribution of SERT on an “altered” vimentin network, the translocation of SERT from the plasma membrane is accelerated on the 5HT-altered vimentin network. Thus, in plasma of hypertensive subjects in which 5HT reaches a high level, the platelet SERT may continue to clear plasma 5HT with a lower Vmax, most likely until the plasma 5HT levels come back to the physiological level. Therefore, to the best of our 
knowledge, this is the first study to identify a sequence on the C-terminus of SERT that regulates the rate of 5HT uptake by altering the density of SERT.