EFFECT OF HUMAN DEFENSINS ON THE CYTOPLASMIC CA2+ CONTENT IN PLATELETS

The effect of the total fraction of human defensins (HNP-1, HNP-2, and HNP-3) on the cytoplasmic Ca2+ content ([Ca2+](i)) in the platelets of healthy donors was studied. At concentrations of 0.1-40 mu g/ml and an incubation time of 10 min defensins have no effect on [Ca2+](i) in platelets labeled with Fura-2AM. However, at higher concentrations (100 mu g/ml) they increased platelet [Ca2+](i). In addition, defensins (40 mu g/ml>) inhibited the Ca2+ increase in platelets induced by thrombin, adenosine diphosphate, and the lipopolysaccharide of S. typhimurium endotoxin. The most pronounced inhibitory effect was observed in a suspension of thrombin-stimulated platelets. It is shown that the effect of human defensins on the functional activity of platelets is due to the alterations in the intracellular Ca2+.