Knapp R J, Sharma S D, Toth G, Duong M T, Fang L, Bogert C L, Weber S J, Hunt M, Davis T P, Wamsley J K
Department of Pharmacology, University of Arizona, College of Medicine, Tucson.
J Pharmacol Exp Ther. 1991 Sep;258(3):1077-83.
[D-Pen2,4'-125I-Phe4,D-Pen5]enkephalin ([125I]DPDPE) is a highly selective radioligand for the delta opioid receptor with a specific activity (2200 Ci/mmol) that is over 50-fold greater than that of tritium-labeled DPDPE analogs. [125I]DPDPE binds to a single site in rat brain membranes with an equilibrium dissociation constant (Kd) value of 421 +/- 67 pM and a receptor density (Bmax) value of 36.4 +/- 2.7 fmol/mg protein. The high affinity of this site for delta opioid receptor ligands and its low affinity for mu or kappa receptor-selective ligands are consistent with its being a delta opioid receptor. The distribution of these sites in rat brain, observed by receptor autoradiography, is also consistent with that of delta opioid receptors. Association and dissociation binding kinetics of 1.0 nM [125I] DPDPE are monophasic at 25 degrees C. The association rate (k + 1 = 5.80 +/- 0.88 X 10(7) M-1 min-1) is about 20- and 7-fold greater than that measured for 1.0 nM [3H DPDPE and 0.8 nM [3H] [D-Pen2,4'-Cl-Phe4, D-Pen5]enkephalin, respectively. The dissociation rate of [125I]DPDPE (0.917 +/- 0.117 X 10(-2) min-1) measured at 1.0 nM is about 3-fold faster than is observed for either of the other DPDPE analogs. The rapid binding kinetics of [125I]DPDPE is advantageous because binding equilibrium is achieved with much shorter incubation times than are required for other cyclic enkephalin analogs. This, in addition to its much higher specific activity, makes [125I]DPDPE a valuable new radioligand for studies of delta opioid receptors.
[D-青霉胺2,4'-125I-苯丙氨酸4,D-青霉胺5]脑啡肽([125I]DPDPE)是一种对δ阿片受体具有高度选择性的放射性配体,其比活度(2200居里/毫摩尔)比氚标记的DPDPE类似物高50倍以上。[125I]DPDPE与大鼠脑膜中的单一位点结合,平衡解离常数(Kd)值为421±67皮摩尔,受体密度(Bmax)值为36.4±2.7飞摩尔/毫克蛋白。该位点对δ阿片受体配体的高亲和力及其对μ或κ受体选择性配体的低亲和力与其作为δ阿片受体一致。通过受体放射自显影观察到的这些位点在大鼠脑中的分布也与δ阿片受体的分布一致。1.0纳摩尔[125I]DPDPE的结合和解离动力学在25℃下是单相的。结合速率(k + 1 = 5.80±0.88×10(7) M-1分钟-1)分别比1.0纳摩尔[3H]DPDPE和0.8纳摩尔[3H][D-青霉胺2,4'-氯苯丙氨酸4,D-青霉胺5]脑啡肽测得的速率大约高20倍和7倍。在1.0纳摩尔下测得的[125I]DPDPE的解离速率(0.917±0.117×10(-2)分钟-1)比其他DPDPE类似物中的任何一种观察到的解离速率快约3倍。[125I]DPDPE的快速结合动力学是有利的,因为与其他环脑啡肽类似物所需的孵育时间相比,它能在更短的孵育时间内达到结合平衡。这一点,再加上其更高的比活度,使得[125I]DPDPE成为研究δ阿片受体的一种有价值的新型放射性配体。