CHARACTERIZATION OF THE BINDING OF LEUKOTRIENE B-4 TO MACROPHAGES OF THE RAINBOW-TROUT ONCORHYNCHUS-MYKISS

The binding of leukotriene B-4 (LTB(4)) to macrophages from the head k idney of the rainbow trout Oncorhynchus mykiss was measured. Binding o f [H-3]LTB(4) achieved a steady state after approximately 30 min of in cubation and was 30% reversible in the presence of a minimum of 1000-f old excess of LTB(4). Scatchard analysis of the kinetics of LTB(4) bin ding over a range of [H-3]LTB(4) concentrations indicated the existenc e of only a single class of receptor with a dissociation constant, K-D , of 0.14 nmol l(-1) and a maximum receptor density, B-max, of approxi mately 17 800 sites per macrophage. The LTB(4) receptor antagonist LY2 23982 was ineffective in inhibiting the binding of [H-3]LTB(4) to trou t macrophages, although another receptor antagonist, LTB(4)-dimethylam ide, displaced a maximum of 25% of the total binding, LTB(5) was equal ly effective as LTB(4) at displacing [H-3]LTB(4), while other eicosano ids tested were without significant effect. It is suggested that the p utative receptors for LTB(4) on trout macrophages are similar to the h igh-affinity receptors for this compound reported to occur on mammalia n granulocytes, although any structural similarities of the binding si tes await further investigation.