Characterisation of the Binding of Leukotriene B₄ To Macrophages of the Rainbow Trout Oncorhynchus Mykiss

The binding of leukotriene B₄ (LTB₄) to macrophages from the head kidney of the rainbow trout Oncorhynchus mykiss was measured. Binding of [³H]LTB₄ achieved a steady state after approximately 30 min of incubation and was 30 % reversible in the presence of a minimum of 1000-fold excess of LTB₄. Scatchard analysis of the kinetics of LTB₄ binding over a range of [³H]LTB₄ concentrations indicated the existence 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 approximately 17 800 sites per macrophage. The LTB₄ receptor antagonist LY223982 was ineffective in inhibiting the binding of [³H]LTB₄ to trout macrophages, although another receptor antagonist, LTB₄-dimethylamide, displaced a maximum of 25 % of the total binding. LTB₅ was equally effective as LTB₄ at displacing [³H]LTB₄, while other eicosanoids tested were without significant effect. It is suggested that the putative receptors for LTB₄ on trout macrophages are similar to the high-affinity receptors for this compound reported to occur on mammalian granulocytes, although any structural similarities of the binding sites await further investigation.