Molinari E J, North P C, Dubocovich M L
Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago 60611-3008, USA.
Eur J Pharmacol. 1996 Apr 22;301(1-3):159-68. doi: 10.1016/0014-2999(95)00870-5.
We now describe the preparation and characterization of a novel radioligand, 2-[125I]iodo-5-methoxy-carbonylamino-N-acetyltryptamine (2-[125I]MCA-NAT), with high affinity and pharmacological selectivity for melatonin ML2 receptor sites. 2-[125I]MCA-NAT was prepared by introducing an [125I]iodine molecule on carbon 2 of 5-MCA-NAT (5-methoxycarbonylamino N-acetyltryptamine), a selective melatonin ML2 receptor ligand. The specific binding (88%) of 2-[125I]MCA-NAT (50 pM) to whole washed hamster brain membranes showed rapid kinetics of association/dissociation, and was of high affinity and saturable (Kd value = 116 +/- 14 pM; Bmax value = 15.5 +/- 1.8 fmol/mg protein, n = 3). 2-[125I]MCA-NAT showed no affinity for melatonin ML1 receptors of chicken retina. Competition curves of various melatonin analogues for 2-[125I]MCA-NAT binding to hamster brain, testes and kidney were monophasic and showed a pharmacological order of affinities (Ki values for brain, nM) identical to that of the ML2 sites [2-iodomelatonin (0.77) > 6-chloro-2-methyl-melatonin (2.56) > 6-chloromelatonin (6.8) > prazosin (21.7) > or = N-acetylserotonin (23.3 nM) > or = 5-MCA-NAT (29.5) > or = melatonin (83.9) > luzindole (1687) > serotonin (2120)]. Affinity constants for competition of melatonin analogues on [125I]MCA-NAT binding to hamster brain, testes, and kidney correlated significantly [r = 0.962, P < 0.001, n = 9; r = 0.982, P < 0.0001, n = 13; r = 0.975, P < 0.0001, n = 9, respectively) with the affinities determined on 2-[125I]iodomelatonin binding to ML2 sites (hamster brain) but not to ML1 sites (chicken retina, r = 0.33, P > 0.05, n = 16). In conclusion, 2-[125I]MCA-NAT is a specific radioligand for the identification and characterization of ML2 binding sites in brain and peripheral tissues.
我们现在描述一种新型放射性配体2-[¹²⁵I]碘-5-甲氧基羰基氨基-N-乙酰色胺（2-[¹²⁵I]MCA-NAT）的制备和特性，它对褪黑素ML2受体位点具有高亲和力和药理学选择性。2-[¹²⁵I]MCA-NAT是通过将[¹²⁵I]碘分子引入5-MCA-NAT（5-甲氧基羰基氨基N-乙酰色胺）的2位碳上制备而成，5-MCA-NAT是一种选择性褪黑素ML2受体配体。2-[¹²⁵I]MCA-NAT（50 pM）与全洗过的仓鼠脑膜的特异性结合（88%）显示出快速的结合/解离动力学，具有高亲和力且可饱和（Kd值 = 116 ± 14 pM；Bmax值 = 15.5 ± 1.8 fmol/mg蛋白质，n = 3）。2-[¹²⁵I]MCA-NAT对鸡视网膜的褪黑素ML1受体没有亲和力。各种褪黑素类似物对2-[¹²⁵I]MCA-NAT与仓鼠脑、睾丸和肾脏结合的竞争曲线是单相的，并且显示出与ML2位点相同的药理学亲和力顺序（脑的Ki值，nM）[2-碘褪黑素（0.77）> 6-氯-2-甲基褪黑素（2.56）> 6-氯褪黑素（6.8）> 哌唑嗪（21.7）> 或 = N-乙酰血清素（23.3 nM）> 或 = 5-MCA-NAT（29.5）> 或 = 褪黑素（83.9）> 鲁辛朵（1687）> 血清素（2120）]。褪黑素类似物对[¹²⁵I]MCA-NAT与仓鼠脑、睾丸和肾脏结合竞争的亲和力常数与在2-[¹²⁵I]碘褪黑素与ML2位点（仓鼠脑）结合但不与ML1位点（鸡视网膜，r = 0.33，P > 0.05，n = 16）结合时测定的亲和力显著相关[r分别为0.962，P < 0.001，n = 9；r = 0.982，P < 0.0001，n = 13；r = 0.975，P < 0.0001，n = 9]。总之，2-[¹²⁵I]MCA-NAT是一种用于鉴定和表征脑和外周组织中ML2结合位点的特异性放射性配体。
