Specific binding of leukotriene B4 to guinea pig lung membranes

We have demonstrated binding sites for LTB4 in guinea pig lung membranes. Binding of [3H]-LTB4 was of high affinity (Kd = 0.76 nM), saturable and linear with protein concentration (0.2-1.2 mg/ml). Scatchard and Hill's plot analysis indicated a single class of binding site with a Hill's coefficient of 0.99 +/- 0.08 (n = 4). [3H]-LTB4 was unmetabolized during incubation with membrane preparations, as indicated by high performance liquid chromatography. Divalent cations such as Mg2+ and Ca2+ enhanced binding capacity without changing the Kd. Na+ ions decreased binding in a concentration-dependent manner. Guanine nucleotides, GTP, GTP gamma S and Gpp(NH)p also decreased the number of binding sites. Finally, competition experiments demonstrated the following order of potency for displacement of [3H]-LTB4 from its receptor site: LTB4 greater than 20-OH-LTB4 much greater than 20-COOH-LTB4 = 6-trans-12-epi-LTB4 greater than LTC4 = LTD4 = 5-HETE. These data indicate that a specific LTB4 receptor, in addition to the previously documented LTC4 and LTD4 receptors, exists in guinea pig lung.