Binding of dexamethasone and its effect on histamine release from rat mast cells.
Purified rat peritoneal mast cells were incubated for 20 h with or without dexamethasone (4 x 10(-6) M) and then passively sensitized with serum from Trichinella spiralis-infected rats. The release of histamine using various secretagogues (concanavalin A, crude antigen of T. spiralis and polymyxin B) was determined. Dexamethasone treatment markedly inhibited IgE-dependent release of histamine (from 33.9 +/- 5.0% to 12.4 +/- 5.1% and from 39.8 +/- 7.9% to 14.2 +/- 6.5% of total cellular histamine content, respectively) whereas histamine release stimulated by the nonimmunological stimulus, polymyxin B was unaffected by this steroid. This suggests that the effects of dexamethasone cannot be exclusively explained by inhibition of phospholipases. Specific binding of 3H-dexamethasone to purified mast cells displayed sigmoidal dependence on concentration which may be the result of either negative cooperativity or the presence of a different class of binding sites. Two saturation plateaux at 20-30 x 10(-9) M and 70-90 x 10(-9) M were observed. The equilibrium dissociation constant for the higher affinity binding sites was Kd1 = 1.9 x 10(-8) M and represented 25,290 sites/cell, whereas the apparent Kd2 for lower affinity sites amounted to 5.5 x 10(-8) M and represented about 120,000 sites/cell.
Wałajtys-Rode
E
E
Institute of Internal Medicine, Warsaw Medical School, Poland.
Dabrowski
A
A
Grubek-Jaworska
H
H
Machnicka
B
B
Droszcz
W
W
D000818:Animals; D000941:Antigens / Q000008:administration & dosage; D001665:Binding Sites; D003208:Concanavalin A / Q000494:pharmacology; D003907:Dexamethasone / Q000378:metabolism* / Q000494:pharmacology; D006636:Histamine Release / Q000187:drug effects*; D006801:Humans; D007073:Immunoglobulin E; D066298:In Vitro Techniques; D007700:Kinetics; D008407:Mast Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D011112:Polymyxin B / Q000494:pharmacology; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000378:metabolism
D000941:Antigens; D011965:Receptors, Glucocorticoid; C028697:dexamethasone receptor; D003208:Concanavalin A; D007073:Immunoglobulin E; D003907:Dexamethasone; D011112:Polymyxin B