Serotonin binding proteins from human blood platelets. An experimental model system for studies on properties of synaptic vesicles.

Serotonin uptake, binding and release were studied in human blood platelets. The uptake showed marked individual differences while the loss of 5-HT during resuspension of the 5-HT loaded platelets was constant. The existence of 5-HT binding proteins was demonstrated by equilibrium dialysis, gel filtration on a column equilibrated with 5-HT, affinity chromatography on a 5-HT-Sepharose column and polyacryl-amide disc gel electrophoresis experiments. After incubation of the platelet extract in the presence of [14-C]5-HT, electrophoretic and autoradiographic analysis demonstrated the presence of three 5-HT binding proteins, two of which were soluble glycoproteins specific for serotonin.