Minneman K P, Fox A W, Abel P W
Mol Pharmacol. 1983 Mar;23(2):359-68.
The interaction of agonists and antagonists with alpha 1-adrenergic receptors in rat vas deferens was examined using radioligand binding assays and contractility measurements. 125I-Labeled BE 2254 (125IBE) was found to bind rapidly and reversibly to a single class of high-affinity binding sites in homogenates of rat vas deferens. The k1 for association was 3.8 X 10(7) 1/mole-sec, the k-1 for dissociation was 2.3 X 10(-3) sec-1, and the KD was 105 pM. The order of potency for antagonists inhibiting 125IBE binding was prazosin greater than indoramin greater than phentolamine greater than yohimbine. Norepinephrine, phenylephrine, and other alpha-adrenergic agonists produced dose-dependent contractions of whole vas deferens in vitro. This contractile response was competitively inhibited by alpha-adrenergic blocking drugs with the same potency order observed for inhibition of specific 125IBE binding. Comparison of pA2 values for alpha 1- and alpha 2-selective antagonists competitively inhibiting contractile responses to norepinephrine, epinephrine, or phenylephrine suggested that these drugs caused their contractile effects solely through alpha 1-adrenergic receptors, and that there were no alpha 2-adrenergic receptors mediating contraction in this tissue. The pA2 values for antagonist inhibition of alpha-adrenergic receptor-mediated contractile responses were highly correlated (r = 0.995) with the KD values for antagonist inhibition of 125IBE binding in this tissue. The EC50 values for partial agonists were also highly correlated with the KD values for inhibition of 125IBE binding in vas deferens. However, the EC50 values of full agonists in causing contraction were in general 10- to 100-fold lower than the KD values for inhibiting 125IBE binding, possibly representing a substantial "spare receptor" population in this tissue. The results suggest that rat vas deferens contains a homogeneous population of alpha 1-adrenergic receptors mediating the contractile response to norepinephrine, that these receptors can be directly labeled with 125IBE, and that there may be a nonlinear relationship between agonist occupancy of alpha 1-adrenergic receptors and the functional response of this tissue.
运用放射性配体结合分析和收缩性测量方法，研究了激动剂和拮抗剂与大鼠输精管中α1 - 肾上腺素能受体的相互作用。发现125I标记的BE 2254（125IBE）能快速且可逆地与大鼠输精管匀浆中的一类单一高亲和力结合位点相结合。结合的k1为3.8×10(7) 1/摩尔·秒，解离的k - 1为2.3×10(-3) 秒-1，KD为105皮摩尔。抑制125IBE结合的拮抗剂效力顺序为：哌唑嗪＞吲哚拉明＞酚妥拉明＞育亨宾。去甲肾上腺素、苯肾上腺素及其他α - 肾上腺素能激动剂在体外能使整个输精管产生剂量依赖性收缩。这种收缩反应被α - 肾上腺素能阻断药物竞争性抑制，其效力顺序与抑制特异性125IBE结合时观察到的顺序相同。比较α1和α2选择性拮抗剂竞争性抑制对去甲肾上腺素、肾上腺素或苯肾上腺素收缩反应的pA2值，表明这些药物仅通过α1 - 肾上腺素能受体产生收缩作用，且该组织中不存在介导收缩的α2 - 肾上腺素能受体。拮抗剂抑制α - 肾上腺素能受体介导的收缩反应的pA2值与该组织中拮抗剂抑制125IBE结合的KD值高度相关（r = 0.995）。部分激动剂的EC50值也与输精管中抑制125IBE结合的KD值高度相关。然而，完全激动剂引起收缩的EC50值通常比抑制125IBE结合的KD值低10至100倍，这可能表明该组织中存在大量“备用受体”。结果表明，大鼠输精管含有介导对去甲肾上腺素收缩反应的同质α1 - 肾上腺素能受体群体，这些受体可用125IBE直接标记，且α1 - 肾上腺素能受体的激动剂占有率与该组织的功能反应之间可能存在非线性关系。
