Modulation of ligand binding to leukotriene B4 receptors on guinea pig lung membranes by sulfhydryl modifying reagents

Abstract

We investigated the mechanism and modulation of 3H-labeled leukotriene B4 (LTB4) binding to guinea pig lung membranes. [3H] LTB4 bound specifically and rapidly (Kobs = 0.06 +/- 0.006 min-1) to high affinity (Kd = 0.63 +/- 0.06 nM) and saturable (Bmax = 224 +/- 16 fmol/mg) sites without cooperativity (nH = 1.05). Bound ligand was partially (70%) dissociated with excess LTB4 or the selective antagonist U-75,302. Complete dissociation could be achieved with either LTB4 or U-75,302 in combination with 10 microM GTP gamma S. A series of structural analogs and selective antagonists inhibited binding in a competitive manner with the following order: LTB4 much greater than 20-(OH)-LTB4 greater than LTB5 greater than LTB-dimethylamide = U-75,302 greater than 12(R)-hydroxy-eicosatetraenoic acid greater than 5(S),12(S)-dihydroxy,6-trans,8-cis,10-trans,14-cis-ETE greater than 12(S)-hydroxy-eicosatetraenoic acid much greater than trans-LTB4 isomers. 5(S)-hydroxy-eicosatetraenoic acid, prostaglandins, peptide-leukotrienes and platelet-activating factor (at 10 microM each) did not inhibit, providing evidence that [3H]LTB4 bound to specific receptors on guinea pig lung membranes. N-Ethylmaleimide (NEM) and p-chloromercuriphenyl sulfonic acid (PCMP) inhibited binding (IC50 = 144 +/- 66 and 4.6 +/- 1.0 microM, respectively) in an irreversible manner, as evident by an inability to overcome the inhibition by extensive washing.(ABSTRACT TRUNCATED AT 250 WORDS)