title: Norepinephrine transporter function and desipramine: residual drug effects versus short-term regulation.
abstract: Previous research has shown that exposure of norepinephrine transporter (NET)-expressing cells to desipramine (DMI) downregulates the norepinephrine transporter, although changes in the several transporter parameters do not demonstrate the same time course. Exposures to desipramine for <1 day reduces only radioligand binding and uptake capacity while transporter-immunoreactivity is unaffected. Recent demonstration of persistent drug retention in cells following desipramine exposures raises the possibility that previous reported changes in the norepinephrine transporter may be partly accountable by residual drug. In this study, potential effects of residual desipramine on norepinephrine transporter binding and uptake were re-evaluated following exposures of PC12 cells to desipramine using different methods to remove residual drug. Using a method that minimizes residual drug, exposure of intact PC12 cells to desipramine for 4h had no effect on uptake capacity or [(3)H]nisoxetine binding to the norepinephrine transporter, while exposures for > or =16 h reduced uptake capacity. Desipramine-induced reductions in binding to the transporter required >24 h or greater periods of desipramine exposure. This study confirms that uptake capacity of the norepinephrine transporter is reduced earlier than changes in radioligand binding, but with a different time course than originally shown. Special pre-incubation procedures are required to abolish effects of residual transporter inhibitor when studying inhibitor-induced transporter regulation.
authors.affiliation: Department of Psychiatry and Human Behavior, The University of Mississippi Medical Center, Jackson, 39216, USA. gordway@psychiatry.umsmed.edu
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Ordway
authors.forename: Weihong
authors.initials: W
authors.lastname: Jia
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Meng-Yang
authors.initials: MY
authors.lastname: Zhu
authors.forename: Prashant
authors.initials: P
authors.lastname: Mandela
authors.forename: Jun
authors.initials: J
authors.lastname: Pan
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology; D018759:Adrenergic Uptake Inhibitors / Q000008:administration & dosage; D000818:Animals; D016477:Artifacts; D003891:Desipramine / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D008657:Metabolic Clearance Rate; D050484:Norepinephrine Plasma Membrane Transport Proteins; D016716:PC12 Cells; D011865:Radioisotope Dilution Technique; D051381:Rats; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D027981:Symporters / Q000378:metabolism*; D013997:Time Factors
chemical_list: D018759:Adrenergic Uptake Inhibitors; D050484:Norepinephrine Plasma Membrane Transport Proteins; C493226:Slc6a2 protein, rat; D027981:Symporters; D003891:Desipramine