Lepiku M, Rinken A, Järv J, Fuxe K
Institute of Chemical Physics, Tartu University, Estonia.
Neurochem Int. 1996 May-Jun;28(5-6):591-5. doi: 10.1016/0197-0186(95)00123-9.
The binding kinetics of the specific dopamine D2 antagonist [3H]raclopride to dopamine D2 receptors in rat neostriatum were studied. The pseudo-first-order rate constants of [3H]raclopride binding with these membranes revealed a hyperbolic dependence upon the antagonist concentration, indicating that the reaction had at least two consecutive and kinetically distinguishable steps. The first step was fast binding equilibrium, characterized by the dissociation constant KA = 12 +/- 3 nM. The following step corresponded to a slow isomerization of the receptor-antagonist complex, characterized by the isomerization equilibrium constant Ki = 0.11. The dissociation constant Kd = 1.3 nM, calculated from these kinetic data, was similar to Kd = 2.4 nM, determined from equilibrium binding isotherm for the radioligand. Implications of the complex reaction mechanism on dopamine D2 receptor assay by [3H]raclopride were discussed.
研究了特异性多巴胺D2拮抗剂[3H]雷氯必利与大鼠新纹状体中多巴胺D2受体的结合动力学。[3H]雷氯必利与这些膜结合的伪一级速率常数显示出对拮抗剂浓度的双曲线依赖性，表明该反应至少有两个连续且动力学上可区分的步骤。第一步是快速结合平衡，其解离常数KA = 12±3 nM。接下来的步骤对应于受体 - 拮抗剂复合物的缓慢异构化，其异构化平衡常数Ki = 0.11。根据这些动力学数据计算出的解离常数Kd = 1.3 nM，与通过放射性配体平衡结合等温线测定的Kd = 2.4 nM相似。讨论了这种复杂反应机制对用[3H]雷氯必利进行多巴胺D2受体测定的影响。
