Vol. 53, Issue 4, 750-758, April 1998

Identification and Characterization of Two Cysteinyl-Leukotriene High Affinity Binding Sites with Receptor Characteristics in Human Lung Parenchyma

Valérie Capra, Simonetta Nicosia, Daniela Ragnini, Maurizio Mezzetti, Dietrich Keppler, and G. Enrico Rovati

Laboratory of Molecular Pharmacology (V.C., S.N., D.R., G.E.R.), Institute of Pharmacological Sciences, University of Milan, 20133 Milan, Italy, IRCCS European Institute of Oncology (M.M.), Department of Thoracic Surgery, Milan, Italy, and Deutsches Krebsforschungszentrum (D.K.), Division of Tumor Biochemistry, Heidelberg, Germany

We report the characterization of two distinct binding sites with receptor characteristics for leukotriene (LT)D₄ and LTC₄ in membranes from human lung parenchyma. The use of S-decyl-glutathione allowed us to characterize a previously unidentified high affinity binding site for LTC₄. Computerized analysis of binding data revealed that each leukotriene interacts with two distinct classes of binding sites (K_d = 0.015 and 105 nM for LTC₄ and 0.023 and 230 nM for LTD₄) and that despite cross-reactivity, the two high affinity sites are different entities. LTD₄ binding sites displayed features of G protein-coupled receptors, whereas LTC₄ binding sites did not show any significant modulation by guanosine-5'-(,-imido)triphosphate or stimulation of GTPase activity. The antagonists ICI 198,615 and SKF 104353 were unselective for the high and low affinity states of LTD₄ receptor, whereas only SKF 104353 was able to recognize the two [³H]LTC₄ binding sites although with different affinities. These data indicate that in human lung parenchyma, LTD₄ and LTC₄ recognize two different binding sites; these binding sites are different entities; and for LTD₄, the two binding sites represent the interconvertible affinity states of a G protein-coupled receptor, whereas for LTC₄, the high affinity site is likely to be a specific LTC₄ receptor.