The binding of [3H] leukotriene C4 to guinea-pig lung membranes. The lack of correlation of LTC4 functional activity with binding affinity

High affinity binding sites for [3H]leukotriene C4 ([3H]LTC4) have been identified and characterised in guinea-pig lung membranes. [3H]LTC4 bound to these membranes with a pharmacological specificity totally distinct to that previously observed for [3H]LTD4 binding in guinea-pig lung. Scatchard analysis of saturation binding data showed a single class of binding sites, with a dissociation constant (KD) of 52.6 +/- 4.9 nM and a density (Bmax) of 30 +/- 12 pmol/mg membrane protein. The binding was inhibited with high affinity by a variety of glutathione-containing leukotriene analogues. Most notable was the inhibition by 1,2,3,4-tetranor LTC4 (Ki = 118 nM) and S-decylglutathione (Ki = 154 nM) since neither of these compounds were contractile agonists on guinea-pig parenchymal strips or guinea-pig ileum nor were they antagonists of LTC4-induced contractions of these smooth muscle preparations. These results indicate that the observed binding of [3H]LTC4 to guinea-pig lung membranes is not to a contractile receptor.