THE INFLUENCE OF GANGLIOSIDES ON BINDING AND UPTAKE OF SEROTONIN BY PLATELETS

The influence of G(M1), G(M3), G(D3) and G(T1b) gangliosides on bindin g and uptake of serotonin by human platelets has been investigated, us ing the radioligand method. The platelets isolated from human blood we re loaded with gangliosides. Serotonin binding with modified and intac t platelets was detected at 0 degrees C. The effect depended on the ga nglioside structure: G(T1b) increased by 40-60% and G(M1) G(M3) G(D3) decreased by 20-40% the number of serotonin receptor binding sites (K- d value was 10 +/- 10 nM). At the same time none of the tested ganglio sides affected the receptor affinity to serotonin. Serotonin uptake by modified and intact platelets was determined at 37 degrees C. It has been demonstrated that the loading of platelets with G(T1b) resulted i n an increase of the maximum speed of serotonin uptake upto 1,fi-fold. This implies an increase in the number of site of binding of the,rece ptor intermediating the uptake of biogenic amine into the cell. Beside s, it has been found that G(T1b) being incorporated by the platelet me mbrane, promotes the extention of cellular capacity for serotonin. A c onclusion has been made that the gangliosides incorporated by the plat elet membrane may influence the conformation of the serotonin receptor .