The active transport of 5-HT byplatelet SERT is thought to be important in maintaining thecirculating concentration of 5-HT below the levels required toactivate vascular smooth cells and platelet 5-HT receptors(Stoltz, 1985; Nemeroff et al., 1998; Musselman et al., 2002).Therefore, the above-mentioned findings suggest that SERTfunction in platelets may be regulated by kinases and phos-phatases linked to endogenous receptors and that this regu-lation may play a role in maintaining blood 5-HT levels.