Wiest S A, Steinberg M I
Lilly Research Laboratories, Eli Lilly and Company Indianapolis, IN 46285, USA.
Life Sci. 1997;60(9):605-15. doi: 10.1016/s0024-3205(96)00639-x.
Recently, a new imidazoline (I2) ligand, [3H]2-(2-benzofuranyl)-2-imidazoline (BFI) was shown to be more selective for I2 vs alpha 2 binding in rodent brain. We characterized [3H]BFI binding in human brain cortex and lateral reticular nucleus (NRL). Membranes were incubated with [3H]BFI at 22 degrees C in 50 mM Tris, 1.5 mM EDTA at pH 7.5. Saturation experiments with [3H]BFI (0.5-80 nM) were analyzed using non-linear curve fitting. The NRL had 4X more binding sites than cortex with similar affinity (Bmax = 2085 +/- 732 and 471 +/- 41 fmol/mg protein; KD = 9.3 +/- 3.5 and 11.9 +/- 2.7 nM, respectively). In competition studies, cortical [3H]BFI binding was displaced in order of decreasing potency by clorgyline > BFI > or = cirazoline > idazoxan > or = guanabenz > clonidine > RX821002. The monoamine oxidase (MAO) inhibitor tranylcypromine (TCP) (1 nM-10 microM), markedly enhanced [3H]BFI binding in both NRL and cortex. Enhanced binding was maximal at 300 nM (12 X control) and returned to baseline at 30 microM. Potentiation was not seen with pargyline or clorgyline. TCP did not effect [3H]BFI binding in rat cortex, or [3H]idazoxan binding in human cortex and NRL. In human cortex, inhibition of MAO by preincubation with pargyline (10 micro M) abolished the TCP effect. Upon preincubation with TCP, the stimulation of [3H]BFI binding was dose-dependently related to a simultaneous inhibition of MAO. Thus, [3H]BFI labels a site in human NRL and cortex that appears similar to the previously described I2 site labeled by [3H]idazoxan. However, [3H]BFI binding is dramatically stimulated by TCP in human brain via a mechanism dependent on endogenous MAO activity.
最近，一种新的咪唑啉（I2）配体，[3H]2-（2-苯并呋喃基）-2-咪唑啉（BFI）在啮齿动物脑中显示出对I2比对α2结合更具选择性。我们对人脑皮质和外侧网状核（NRL）中的[3H]BFI结合进行了表征。在22℃下，将膜与[3H]BFI在50 mM Tris、1.5 mM EDTA（pH 7.5）中孵育。使用非线性曲线拟合分析[3H]BFI（0.5 - 80 nM）的饱和实验。NRL的结合位点比皮质多4倍，亲和力相似（Bmax分别为2085±732和471±41 fmol/mg蛋白质；KD分别为9.3±3.5和11.9±2.7 nM）。在竞争研究中，皮质[3H]BFI结合被氯吉兰> BFI >或=西拉唑啉>伊达唑胺>或=胍法辛>可乐定> RX821002以效力递减的顺序取代。单胺氧化酶（MAO）抑制剂反苯环丙胺（TCP）（1 nM - 10 μM）显著增强了NRL和皮质中的[3H]BFI结合。增强的结合在300 nM时最大（为对照的12倍），并在30 μM时恢复到基线。帕吉林或氯吉兰未观察到增强作用。TCP对大鼠皮质中的[3H]BFI结合或人皮质和NRL中的[3H]伊达唑胺结合没有影响。在人皮质中，用帕吉林（10 μM）预孵育抑制MAO消除了TCP的作用。在用TCP预孵育后，[3H]BFI结合的刺激与MAO的同时抑制呈剂量依赖性相关。因此，[3H]BFI标记了人NRL和皮质中的一个位点，该位点似乎与先前描述的由[3H]伊达唑胺标记的I2位点相似。然而，在人脑中，[3H]BFI结合通过依赖内源性MAO活性的机制被TCP显著刺激。
