Nicosia S, Crowley H J, Oliva D, Welton A F
Prostaglandins. 1984 Mar;27(3):483-94. doi: 10.1016/0090-6980(84)90206-5.
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.
白三烯（LTC4）是过敏反应慢反应物质（SRS - A）的组成成分之一，是豚鼠回肠的强效收缩剂。这种收缩可能是一个受体介导的过程。在此我们报告在豚鼠回肠纵肌的粗制膜制剂中存在3H - LTC4的特异性结合位点。在4℃、20 mM丝氨酸 - 硼酸盐存在的条件下，结合量随蛋白质浓度呈线性增加，10分钟达到平衡，加入3×10⁻⁵ M未标记的LTC4后结合是可逆的。解离曲线与存在不止一类结合位点相符。Ca²⁺和Mg²⁺在平衡时极大地增强了3H - LTC4的结合。在5 mM CaCl₂和MgCl₂存在的情况下，不仅LTC4（IC50为10⁻⁷ M），而且LTD4（尽管亲和力低得多，IC50 = 6×10⁻⁵ M）和SRS - A拮抗剂FPL 55712（IC50 = 10⁻⁵ M）都能与3H - LTC4竞争其结合位点。FPL 55712仅能取代结合总量的60 - 70%，而LTC4能取代90 - 95%。这些研究表明豚鼠回肠纵肌中存在多类3H - LTC4结合位点，并且这些结合位点中至少部分可能与LTC4使豚鼠回肠收缩的能力有关。
