Institute of Physiology CAS, 142 20, Prague, Czech Republic.
Department of Experimental and Clinical Pharmacology, University of Minnesota College of Pharmacy, Minneapolis, MN, 55455, USA.
Sci Rep. 2019 Mar 15;9(1):4637. doi: 10.1038/s41598-019-40993-w.
Proper determination of agonist efficacy is essential in the assessment of agonist selectivity and signalling bias. Agonist efficacy is a relative term that is dependent on the system in which it is measured, especially being dependent on receptor expression level. The operational model (OM) of functional receptor agonism is a useful means for the determination of agonist functional efficacy using the maximal response to agonist and ratio of agonist functional potency to its equilibrium dissociation constant (K) at the active state of the receptor. However, the functional efficacy parameter τ is inter-dependent on two other parameters of OM; agonist's K and the highest response that could be evoked in the system by any stimulus (E). Thus, fitting of OM to functional response data is a tricky process. In this work we analyse pitfalls of fitting OM to experimental data and propose a rigorous fitting procedure where K and E are derived from half-efficient concentration of agonist and apparent maximal responses obtained from a series of functional response curves. Subsequently, OM with fixed K and E is fitted to functional response data to obtain τ. The procedure was verified at M and M muscarinic receptors fused with the G G-protein α-subunit. The procedure, however, is applicable to any receptor-effector system.
正确确定激动剂的效能在评估激动剂的选择性和信号转导偏倚方面至关重要。激动剂效能是一个相对的术语，取决于测量的系统，特别是受体表达水平。功能性受体激动作用的操作模型（OM）是一种有用的方法，可通过测量激动剂的最大反应和激动剂在受体活性状态下的功能效价与平衡解离常数（K）的比值来确定激动剂的功能效能。然而，功能效能参数τ与 OM 的另外两个参数密切相关；激动剂的 K 和任何刺激在系统中可以引起的最高反应（E）。因此，将 OM 拟合到功能响应数据是一个棘手的过程。在这项工作中，我们分析了将 OM 拟合到实验数据时的陷阱，并提出了一种严格的拟合程序，其中 K 和 E 是从激动剂的半有效浓度和从一系列功能响应曲线获得的表观最大响应中得出的。随后，使用固定的 K 和 E 的 OM 拟合功能响应数据以获得τ。该程序在与 G 蛋白α亚基融合的 M 和 M 毒蕈碱受体上进行了验证。然而，该程序适用于任何受体-效应器系统。
