Sibley D R, De Lean A, Creese I
J Biol Chem. 1982 Jun 10;257(11):6351-61.
The interactions of dopaminergic agonists and antagonists with binding sites in bovine anterior pituitary membranes have been investigated with radioligand-binding techniques and computer-modeling procedures. 3H-labeled agonist binding is stereospecific, reversible, saturable, and of high affinity. The rank order of catecholamines, phenothiazines, and related drugs in competing for 3H-agonist binding is indicative of interactions with a D-2 dopamine receptor. Both agonist/3H-agonist and antagonist/3H-agonist competition curves are monophasic and noncooperative (nH = 1) with computer analysis indicating a single class of binding sites. Specific 3H-agonist binding can be completely inhibited by guanine nucleotides. GppNHp us the most potent nucleotide followed by GTP and GDP which are equipotent. The equilibrium binding capacity for 3H-labeled antagonists is twice that for 3H-agonists. Unlabeled antagonists inhibit 3H-antagonist binding competitively and exhibit antagonist/3H-antagonist competition curves which model best to a state of homogeneous affinity. In contrast, unlabeled agonists inhibit 3H-antagonist binding in a heterogeneous fashion displaying multiphasic (nH less than 1) competition curves which can be resolved into high and low affinity binding sites. In the presence of saturating concentrations of guanine nucleotides, however, the agonist/3H-antagonist curves model best to a single affinity state which is identical with the low affinity state seen in control curves. The binding data can be explained by postulating two states of the D-2 dopamine receptor, inducible by agonists but not antagonists and modulated by guanine nucleotides.
已运用放射性配体结合技术和计算机建模程序，研究了多巴胺能激动剂和拮抗剂与牛垂体前叶膜中结合位点的相互作用。3H标记的激动剂结合具有立体特异性、可逆性、饱和性且亲和力高。儿茶酚胺、吩噻嗪及相关药物在竞争3H激动剂结合时的排序，表明它们与D-2多巴胺受体存在相互作用。激动剂/3H激动剂和拮抗剂/3H激动剂竞争曲线均为单相且非协同性的（nH = 1），计算机分析表明存在单一类别的结合位点。特异性3H激动剂结合可被鸟嘌呤核苷酸完全抑制。GppNHp是最有效的核苷酸，其次是等效的GTP和GDP。3H标记拮抗剂的平衡结合能力是3H激动剂的两倍。未标记的拮抗剂竞争性抑制3H拮抗剂结合，并呈现出最符合均匀亲和力状态的拮抗剂/3H拮抗剂竞争曲线。相比之下，未标记的激动剂以异质性方式抑制3H拮抗剂结合，呈现多相（nH小于1）竞争曲线，可解析为高亲和力和低亲和力结合位点。然而，在鸟嘌呤核苷酸饱和浓度存在的情况下，激动剂/3H拮抗剂曲线最符合单一亲和力状态，该状态与对照曲线中所见的低亲和力状态相同。结合数据可通过假设D-2多巴胺受体的两种状态来解释，这两种状态可由激动剂而非拮抗剂诱导，并受鸟嘌呤核苷酸调节。
