Platelet-aggregation inhibiting activity of human placental chorioepithelial brush border membrane vesicles and basal plasma membrane vesicles

Summary This laboratory investigated the platelet-aggregation inhibiting activity of human placental brush border membrane vesicles (BBMV) and basal plasma membrane vesicles (BpMV), and obtained the following results. o 1) A strong platelet-aggregation inhibiting activity exists in placental BBMW. In a 20 μg/ml protein concentration, the BBMV completely inhibited the secondary platelet aggregation induced by ADP. In a 40 μg/ml protein concentration, the BBMV completely inhibited the platelet aggregation induced by arachidonic acid and collagen, and in a 200 μg/ml protein concentration, the BBMV completely inhibited the platelet aggregation induced by ristocetin. However, placental BpMV did not show prominent platelet-aggregation inhibiting activity on platelet aggregation induced by ADP, arachidonic acid, collagen, or ristocetin. 2) A strong ADP degrading activity (ADPase activity) in the placental BBMV was found. ADP-degrading activity of the BBMV was 10.5±0.5 μmol/mg protein/minute and ADP-degrading activity of BpMV was 0.6±0.1 μmol/mg protein/minute. 3) The placental BBMV inhibited platelet thromboxane A 2 (TXA 2 ) production. In a 40 μg/ml protein concentration of placental BBMV, a platelet TXA 2 (TXB 2 ) production was almost completely inhibited. BpMV did not show prominent inhibitory activity on platelet TXA 2 (TXB 2 ) production. These results indicate that brush border membrane and basal plasma membrane have a different function in the respect of platelet-aggregation inhibiting activity, and that the brush border membrane may play an important role inhibiting platelet aggregation.