CHARACTERIZATION OF THE LEUKOTRIENE D4 RECEPTOR IN DIMETHYLSULFOXIDE-DIFFERENTIATED-U937 CELLS - COMPARISON WITH THE LEUKOTRIENE-D4 RECEPTOR IN HUMAN LUNG AND GUINEA-PIG LUNG

The leukotriene D4 receptor has been fully characterized by radioligand binding in membrane preparations from dimethyl sulphoxide-differentiated U937 cells, a human monocyte leukemia cell line, and, in parallel experiments, compared with leukotriene D4 receptor found in human lung and guinea-pig lung preparations. [H-3]Leukotriene D4 specific binding in differentiated U937 cell membranes is of high affinity (K(D) = 0.35 nM), saturable (B(max) = 287 fmol/mg protein), with differentiation resulting in a 3-5-fold increase in the number of detectable binding sites. [H-3]Leukotriene D4-specific binding in differentiated U937 cell membranes displays several features of G-protein-coupled receptors, being inhibited by GTP analogues and sodium ions, but increased by divalent cations. These characteristics are shared with [H-3]leukotriene D4-specific binding in human and guinea-pig lung preparations. However, differences between these leukotriene D4 receptor types were observed. [H-3]Leukotriene D4 equilibrium binding to differentiated U937 cell membranes could be dissociated to non-specific binding levels by 1000-fold excess of competing ligand, whereas binding to guinea-pig lung membranes was only partially dissociated under these conditions. In addition, differences in potency were demonstrated in competition studies with leukotriene E4 and leukotriene C4, although leukotriene D4 and the leukotriene D4-receptor antagonists MK-571 and ICI 204,219 were equipotent in competing for [H-3]leukotriene D4-specific binding in all three membranes preparations. In conclusion, the leukotriene D4 receptor in differentiated U937 cell membranes resembles that in human lung, validating the use of this cell line as a suitable source of receptor in the development of potent specific antagonists.