Characteristics and distribution of specific binding sites for leukotriene C4 in human bronchi.
The binding of [3H]leukotriene (LT) C4 to membranes from human bronchi has been characterized. The specific binding, measured at 4 degrees C, was very rapid, equilibrium being attained within 1 to 5 min. The binding was also rapidly reversible and saturable (maximum binding = 187 pmol/mg of protein). LTC4, LTD4, LTE4 and the LT antagonist FPL 55712 competed with [3H]LTC4 for its binding sites, with the following IC50 values: 0.12; 2.3; 30; and 20 microM. Therefore, the binding sites displayed a higher affinity for LTC4 than for the other sulfidopeptide LTs. Computer-assisted analysis of either the saturation or the competition curves for LTC4 indicated the existence of two classes of binding sites with different affinities (Kd1 and Kd2 = 70 nM and 0.58 microM, respectively), in agreement with the curved semilog plot of the dissociation time course. CaCl2 or MgCl2 increased and GTP or 5'-guanylylimidodiphosphate did not decrease the specific binding. In addition, the distribution of the binding sites for [3H]LTC4 along the human respiratory tree was investigated. At a fixed (10 nM) [3H]LTC4 concentration, membranes obtained from bronchi removed at different levels of the airway tree did not bind LTC4 in a significantly different amount. This is compatible with the finding that LTC4 receptors should be present on bronchi of various caliber, as both small and large airways respond to LTs.
Civelli
M
M
Institute of Pharmacological Sciences, University of Milan, Italy.
Oliva
D
D
Mezzetti
M
M
Nicosia
S
S
D001667:Binding, Competitive; D001980:Bronchi / Q000032:analysis* / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D018077:Receptors, Leukotriene; D011982:Receptors, Prostaglandin / Q000032:analysis* / Q000378:metabolism; D013189:SRS-A / Q000378:metabolism*
D018077:Receptors, Leukotriene; D011982:Receptors, Prostaglandin; D013189:SRS-A; D006165:Guanylyl Imidodiphosphate; D006427:Hemin; D006160:Guanosine Triphosphate; D002118:Calcium