MEDIATORS OF COMPLEMENT-INDEPENDENT GRANULOCYTE ACTIVATION DURING HEMODIALYSIS - ROLE OF CALCIUM, PROSTAGLANDINS AND LEUKOTRIENES

Granulocyte activation during haemodialysis using cuprophane membrane is mediated by complement-derived anaphylatoxins C3a and C5a. However, neutrophil degranulation induced by modified cellulosic membranes or synthetic membranes does not correlate with C3a or C5a concentrations. Incubation and recirculation experiments were performed to find out w hich messengers trigger neutrophil degranulation during blood contact with different membrane materials. During in vitro haemodialysis for 2 hours, PMMA and cuprophane induced pronounced degranulation of neutro phils. With PMMA this was associated with increased thromboxane B-2 bu t low C3a levels, while with cuprophane membrane, marked complement ac tivation but only little thromboxane B-2 release was observed. Indomet hacin (10 mu M) nullified all thromboxane B-2 response but could not i nfluence elastase release, indicating that cyclo-oxygenase products ar e not involved in neutrophil degranulation under these conditions. Dur ing incubation of blood with dialysis membranes, inhibition of lipoxyg enase by esculetin or of phospholipase A(2) by hydrocortisone also had no effect on neutrophil degranulation. One messenger involved in gran ulocyte activation might be free cytosolic calcium. Application of dif ferent calcium channel blockers (verapamil, diltiazem, or nitrendipine ) did not influence neutrophil degranulation in incubation experiments , in PMMA or cuprophane membranes. In contrast, chelation of plasmatic calcium by sodium citrate or EDTA blunted elastase release induced by these membranes. This study indicates that calcium is a key mediator required for neutrophil degranulation in complement-activating and non -complement-activating dialysis membranes, while activation of the pro staglandin or leukotriene cascade are not required.