Zhu M Y, Ordway G A
Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson 39216, USA.
J Neurochem. 1997 Jan;68(1):134-41. doi: 10.1046/j.1471-4159.1997.68010134.x.
To investigate the regulation of norepinephrine transporters (NETs) in vitro, we measured the binding of the NET-selective ligand [3H]nisoxetine in homogenates of PC12 cells after exposure of intact cells to the NET inhibitor desipramine (DMI). A 3-day exposure of PC12 cells to DMI robustly reduced the Bmax, but not the KD, of [3H]nisoxetine binding to NETs. Reduction of the binding of [3H]nisoxetine was dependent on both the concentration of DMI and the time of exposure to DMI. Reduction of [3H]nisoxetine binding to NETs produced by a 1-day exposure to DMI reverted to preexposure levels 48 h after cessation of DMI exposure. Similar down-regulation of NETs was found when PC12 cells were exposed to another NET-selective drug, nisoxetine, which is structurally unrelated to DMI. In contrast, exposure of cells to the serotonin transporter-selective drug citalopram, or the NET substrate norepinephrine, had no effects on the binding of [3H]nisoxetine to NETs. The down-regulation of NETs was paralleled by a DMI-induced reduction in the uptake of [3H]norepinephrine in intact PC12 cells. It can be inferred from these data that inhibitors of the NET can down-regulate NETs directly, and do so in the absence of changes in the synaptic concentration of norepinephrine.
为了在体外研究去甲肾上腺素转运体（NETs）的调节机制，我们在完整细胞暴露于NET抑制剂地昔帕明（DMI）后，测量了PC12细胞匀浆中NET选择性配体[3H]尼索西汀的结合情况。PC12细胞暴露于DMI 3天可显著降低[3H]尼索西汀与NETs结合的最大结合量（Bmax），但不影响解离常数（KD）。[3H]尼索西汀结合量的降低既取决于DMI的浓度，也取决于暴露于DMI的时间。暴露于DMI 1天导致的[3H]尼索西汀与NETs结合量的降低在停止DMI暴露48小时后恢复到暴露前水平。当PC12细胞暴露于另一种与DMI结构无关的NET选择性药物尼索西汀时，发现NETs有类似的下调现象。相比之下，细胞暴露于5-羟色胺转运体选择性药物西酞普兰或NET底物去甲肾上腺素，对[3H]尼索西汀与NETs的结合没有影响。NETs的下调与DMI诱导的完整PC12细胞中[3H]去甲肾上腺素摄取减少相平行。从这些数据可以推断，NET抑制剂可直接下调NETs，且在去甲肾上腺素突触浓度无变化的情况下即可发生。
