Abstract: The intracellular calcium in thc rat platelets was measured with fluorescent calcium indicator fura-2, The changes in thc cytoplasmic free calcium werc also studied in the platelets treated with emodin. The results showed that the free Ca²⁺ level was 2l8.40±56.36 nmol/L (n = 13). In fura-2-loaded resting platelets. After administration of CaCl2 (l mmol/L), KCl (120 mmol/L) and thrombin (0.5 u/ml) sequentially, the free Ca²⁺ levels were 297.25±75.03 nmol/L (n = 13). 318.00±86.25 nmol/L (n = l2) and 640.59±62.49 nmol/L (n = 12) respectively. All of the levels were significantly elevated compared with that of the resting platelets (P<0.0l). After pretreatment with emodin for 20 min. the mean platelet [Ca²⁺]i in these resting platelets was 3l6.28±80.25 nmol/L (n = 16). Using above doses of CaCl2, KCl and thrombin , the free Ca²⁺ levels increased to 396.45±107.78 nmol/L (n = 16). 428.02±126.20 nmol/L (n = 5) and 698. 85±122.93 nmol/L (n = 15) respectively The results revealed an obvious increase in [Ca²⁺]i levels compared with that of the resting(P<0.05 and P<0.0l). Further- more, the Ca²⁺ levels were were significantly higher than those of the control groups(P<0.01) except for the thrombin treatment groups.It was suggested that the increase of [Ca²⁺]i induced by emodin in the platelets was due to the influx of Ca²⁺ and the release of Ca²⁺ from intracellular stores.

Key words: Fura-2, Emodin: Calcium, Thrombin, Platelet