Irreversible binding of a carbostyril-based agonist and antagonist to the β-adrenoceptor in DDT<sub>1</sub>MF-2 cells and rat aorta
作者:Malgorzata D Deyrup、Phillip G Greco、Deborah H Otero、Donn M Dennis、Craig H Gelband、Stephen P Baker
DOI:10.1038/sj.bjp.0701801
日期:1998.5
The chemoreactive ligands 5(2‐(((1′‐(4′‐isothiocyanatophenylamino)thiocarbonyl)‐amino)‐2‐methyl‐propyl)amino‐2‐hydroxypropoxy)‐3,4‐dihydrocarbostyril (DCITC) and 8‐hydroxy‐5(2‐(((1′‐(4′‐isothiocya‐natophenylamino)thiocarbonyl)amino)‐2‐methylprop‐2‐yl)amino‐1‐hydroxyethyl)‐carbostyril (HCITC)were synthesized and shown to be potent irreversible antagonist and agonist ligands, respectively, for the β‐adrenoceptor in DDT1 MF‐2 (DDT) cells and the rat isolated aorta.
In DDT cell membranes DCITC and HCITC inhibited (−)[125I]‐iodocyanopindolol (CYP) binding to the β‐adrenoceptor with IC50 values of 1.1 and 18 nM, respectively. (−)‐Isoprenaline inhibited [125I]‐CYP binding with an IC50 of 355 nM. Pretreatment of membranes with either chemoreactive ligand produced a time‐ and concentration‐dependent decrease in the β‐adrenoceptor content, indicating irreversible receptor binding. DCITC at concentrations up to 10 μM did not stimulate cyclic AMP accumulation in DDT cells nor did it amplify forskolin‐stimulated cyclic AMP accumulation.
In the rat isolated aorta, DCITC (0.1 μM) did not affect either the phenylephrine‐mediated tissue contraction or the acetylcholine‐mediated relaxation. DCITC attenuated the maximal (−)‐isoprenaline‐mediated relaxation of a phenylephrine contracted aorta in a concentration‐dependent manner and shifted the dose‐response curves for (−)‐isoprenaline to the right. The DCITC‐induced decrease in maximal response was not reversed by extensive tissue washing. By use of the operational model of agonism, the calculated dissociation constant for (−)‐isoprenaline ws 286 nM and the estimated receptor reserve for this agonist was 23% at the maximal response.
HCITC and (−)‐isoprenaline stimulated cyclic AMP accumulation in DDT cells with pD2 values (negative logarithm to base 10 of EC50) of 7.95 and 7.97, respectively, and both mediated the same maximal stimulation. In the rat isolated aorta, HCITC produced a concentration‐dependent relaxation of the tissue with a pD2 value of 6.62, whereas the pD2 for (−)‐isoprenaline was 7.03. However, HCITC produced a greater maximal relaxation of the tissue than (−)‐isoprenaline. The HCITC‐mediated stimulation of cyclic AMP accumulation and relaxation of the isolated tissue were blocked when the β‐antagonist propranolol was added concurrently. In contrast, once the HCITC‐mediated responses were established, the addition of propranolol did not result in any attenuation indicating that HCITC is an irreversible β‐agonist.
我们合成了化学反应型配体 5(2‐(((1′‐(4′‐异硫氰酸苯基氨基)硫代羰基)氨基)‐2‐甲基-丙基)氨基-2-羟基丙氧基)-3,4-二氢碳酰替洛尔(DCITC)和 8-羟基-5(2‐(((1′‐(4′‐异硫氰酸苯基氨基)硫代羰基)氨基)‐2-甲基丙-2-基)氨基-1-羟基乙基)-碳酰替洛尔(HCITC),并分别证明其为 β-肾上腺素受体在 DDT1 MF-2 (DDT) 细胞和大鼠离体主动脉中的强效不可逆拮抗剂和激动剂配体。在 DDT 细胞膜中,DCITC 和 HCITC 抑制了(-)[125 I] 碘氰洛酚(CYP)与 β-肾上腺素受体的结合,其 IC50 值分别为 1.1 和 18 nM。(-)-异丙肾上腺素对 [125 I]-CYP 结合的抑制作用的 IC50 为 355 nM。用任一化学反应型配体对膜的预处理导致 β-肾上腺素受体含量随时间和浓度的依赖性减少,表明配体与受体的不可逆结合。在 DDT 细胞中,DCITC 甚至在高达 10 μM 浓度时,也不会刺激环磷酸腺苷的积累,也不会放大 Forskolin 刺激的环磷酸腺苷积累。在大鼠离体主动脉中,DCITC(0.1 μM)不会影响苯肾上腺素介导的组织收缩或乙酰胆碱介导的松弛。DCITC 以浓度依赖性方式减弱了苯肾上腺素收缩主动脉的 (-)-异丙肾上腺素介导的最大松弛作用,并使 (-)-异丙肾上腺素的剂量-反应曲线向右移动。DCITC 引起的最大反应减少不能通过充分洗涤组织来逆转。通过使用功效模型,(-)-异丙肾上腺素的解离常数计算为 286 nM,在最大反应时该激动剂的受体储备估计为 23%。在 DDT 细胞中,HCITC 和 (-)-异丙肾上腺素刺激了环磷酸腺苷的积累,其 pD2 值(EC50 的负对数)分别为 7.95 和 7.97,两者介导的最大刺激相同。在大鼠离体主动脉中,HCITC 以浓度依赖性方式引起组织松弛,其 pD2 值为 6.62,而 (-)-异丙肾上腺素的 pD2 值为 7.03。然而,HCITC 产生的最大组织松弛程度大于 (-)-异丙肾上腺素。β-阻滞剂普萘洛尔的共加可阻断 HCITC 介导的环磷酸腺苷积累和离体组织松弛。相反,一旦 HCITC 介导的反应建立,普萘洛尔的添加不会导致任何减弱,表明 HCITC 是一种不可逆的 β-激动剂。