Identification and characterization of leukotriene D4 receptors in adult and fetal human lung

Abstract Leukotriene D 4 (LTD 4 ) receptors were identified and characterized in adult and fetal human lung membranes. Macroscopically normal adult lung tissue was selected from seventeen surgical biopsy specimens, and twenty-seven fetal lung samples were obtained from therapeutic abortions. Binding assays were performed using pooled adult or fetal human lung membranes at 30° under conditions which prevented metabolism of [ 3 H]LTD 4 . Specific binding reached equilibrium within 30 min, remained constant for 60 min, was enhanced by Mg 2+ , and was inhibited by Na + and guanyl-5′-yl-imidodiphosphate. Computer-assisted analyses of saturation binding data showed a single class of binding sites with similar apparent K d (0.15 ± 0.09 and 0.12 ± 0.003 nM) and B max (68 ± 29 and 62 ± 14 fmoles/mg protein) values for adult and fetal samples respectively. Competition binding studies with [ 3 H]LTD 4 showed the same rank order potency for adult and fetal lung receptors (5 S ,6 R -LTD 4 > 5 S , 6 R -LTD 1 > 5 R ,6 S -LTD 4 > 5 S , 6 R -LTE 4 > FPL 55712). A comparison of the receptor binding affinities of these compounds with their smooth muscle contractile agonist (pD 2 ) and antagonist (−log[ K B ) activities in guinea pig lung and trachea showed a good correlation ( r = 0.88), suggesting that the saturable, high-affinity, stereoselective [ 3 H]LTD 4 specific binding sites identified in human lung may be physiologically relevant receptor moieties.