N-Ethylmaleimide Induces Disaggregation of Platelets Preaggregated by ADP and Thrombin and Decreases Cytoplasmic Calcium Level

A. B. Samal^* and E. N. Loiko

Department of Biophysics, Belarus State University, pr. F. Skoriny 4, Minsk, 220050 Belarus; fax: (017) 220-6251; E-mail: samal@phys.bsu.unibel.by

^* To whom correspondence should be addressed.

Received May 19, 1999; Revision received July 26, 1999

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The effect of N-ethylmaleimide (NEM, 1-200 µM) on ADP- and thrombin-induced platelet aggregation and thrombin-induced increase in intracellular Ca²⁺ concentration was studied. Addition of NEM to platelets preaggregated with ADP or thrombin induces platelet disaggregation. The anti-aggregant activity of NEM was different for ADP- and thrombin-induced aggregations. At 200 µM concentration, NEM completely disaggregated ADP-induced aggregates and only partially disaggregated thrombin-aggregated platelets. NEM did not influence the thrombin-induced increase in cytoplasmic Ca²⁺ and had no effect on the basal level of Ca²⁺ in the cytosol of non-activated platelets. However, NEM decreased the level of thrombin-mobilized Ca²⁺ in the cytosol of activated platelets. Thus, NEM can induce disaggregation of ADP- and thrombin-preaggregated platelets by activating a system which removes Ca²⁺ from the platelet cytosol.

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KEY WORDS: platelets, aggregation, disaggregation, N-ethylmaleimide, cytoplasmic calcium, ADP, thrombin

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