Down-regulation of norepinephrine transporters on PC12 cells by transporter inhibitors.
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.
Zhu
M Y
MY
Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson 39216, USA.
Ordway
G A
GA
D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D002452:Cell Count / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003891:Desipramine / Q000494:pharmacology*; D015536:Down-Regulation; D005473:Fluoxetine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D009638:Norepinephrine / Q000493:pharmacokinetics / Q000494:pharmacology; D050484:Norepinephrine Plasma Membrane Transport Proteins; D016716:PC12 Cells / Q000378:metabolism / Q000473:pathology; D051381:Rats; D027981:Symporters; D007507:Therapeutic Irrigation
D000928:Antidepressive Agents; D002352:Carrier Proteins; D050484:Norepinephrine Plasma Membrane Transport Proteins; C493226:Slc6a2 protein, rat; D027981:Symporters; D005473:Fluoxetine; C011386:nisoxetine; D003891:Desipramine; D009638:Norepinephrine