title: Binding sites for 3H-LTC4 in membranes from guinea pig ileal longitudinal muscle.
abstract: Leutriene (LTC4) is one of the components of Slow Reacting Substance of Anaphylaxis (SRS-A) and is a potent constrictor of guinea pig ilea. The contraction is likely to be a receptor-mediated process. Here we report the existence of specific binding sites for 3H-LTC4 in a crude membrane preparation from guinea pig ileal longitudinal muscle. At 4 degrees C in the presence of 20 mM Serine-borate, binding increases linearly with protein concentration, reaches equilibrium in 10 minutes, and is reversible upon addition of 3 x 10(-5) M unlabelled LTC4. The dissociation curve is consistent with the existence of more than one class of binding site. Ca++ and Mg++ greatly enhance the binding of 3H-LTC4 at equilibrium. In the presence of 5 mM CaCl2 and MgCl2 not only LTC4 (IC50 10(-7)M), but also LTD4 (albeit with much lower affinity, IC50 = 6 x 10(-5) M) and the SRS-A antagonist FPL 55712 (IC50 = 10(-5) M) can compete with 3H-LTC4 for its binding sites. FPL 55712 only displaces 60-70% of the total amount bound, while LTC4 displaces 90-95%. These studies indicate that multiple classes of binding sites exist for 3H-LTC4 in guinea pig ileal longitudinal muscle, and that at least part of these binding sites might be related to the ability of LTC4 to contract guinea pig ilea.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002122:Calcium Chloride / Q000494:pharmacology; D002462:Cell Membrane / Q000276:immunology; D006168:Guinea Pigs; D007700:Kinetics; D017999:Leukotriene E4; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D008297:Male; D009132:Muscles / Q000276:immunology*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018077:Receptors, Leukotriene; D013189:SRS-A / Q000031:analogs & derivatives / Q000378:metabolism*; D014316:Tritium
chemical_list: D011956:Receptors, Cell Surface; D018077:Receptors, Leukotriene; D013189:SRS-A; D015636:Magnesium Chloride; D014316:Tritium; D017999:Leukotriene E4; D008274:Magnesium; D002122:Calcium Chloride