Washed human platelets were loaded with the Ca2+-sensitive photoprotein

aequorin. using hypoosmotic shock treatment-technique. Then aggregation and cytoplasmic ionized calcium concentration （ [Ca2+] i） changes in response to collagen or thrombin were measured simultaneously in the aequorin-loaded human platelets with a Platelet Ionized Calcium Aggregometer. 764-3. an active component isolated from the Chinese medicinal herb Salvia Miltiorrhiza Bge

inhibited platelet [Ca2+]i rise as well as aggregation evoked by collagen or thrombin in the presence of extracellular Ca2+. After the extracellular Ca2+. was removed by addition of EGTA

collagen or thrombin. causing no aggregation. still elicited platelet [Ca2+] i rise which reflected Ca2+ mobilization from intraplatelet stores. Under this condition

764-3 could also suppress platelet [Ca2+] i rise. Analysis shows that 764-3 inhibrts platelet Ca2+ influx and Ca2+ mobilization with similar potency. which accounts for its suppression of platelet [Ca2+] i rise

and must contribute to its inhibition of platelet aggregation.