Amphetamine reverses or blocks the operation of the human noradrenaline transporter depending on its concentration: superfusion studies on transfected cells.
Whether amphetamine enhances noradrenergic activity by uptake blockade or a releasing action is still a matter of debate. In order to gain insight into the interaction of amphetamine with the noradrenaline transporter its cDNA was transfected into COS-7 cells (NAT-cells) or cotransfected with the cDNA of the vesicular monoamine transporter (NAT/VMAT-cells); cells were loaded with [3H]noradrenaline, superfused and the efflux analysed for total tritium and [3H]noradrenaline. In NAT-cells amphetamine stimulated [3H]noradrenaline efflux concentration-dependently when added to the superfusion buffer at 0.01, 0.1 and 1 microM. By contrast, 10 or 100 microM amphetamine stimulated efflux to a smaller extent or not at all; however, on switching back to amphetamine-free buffer a prompt increase of efflux was observed. Cocaine did not increase efflux per se and blocked the amphetamine-induced efflux. In NAT/VMAT-cells amphetamine stimulated efflux in a concentration-dependent manner. The effect showed saturation at 1 microM and was not suppressed at higher concentrations. Cocaine also elicited efflux from NAT/VMAT-cells concentration-dependently; the maximum was reached at approximately 1 microM and amounted to only about half of the amphetamine-induced efflux. It is concluded that amphetamine can induce noradrenaline transporter mediated release only at high nanomolar to low micromolar concentrations. At higher concentrations it blocks the noradrenaline transporter; in this case, the releasing action of amphetamine, like that of cocaine, is dependent on a vesicular pool of noradrenaline.
Pifl
C
C
Institute of Biochemical Pharmacology, University of Vienna, Austria. christian.pifl@univie.ac.at
Agneter
E
E
Drobny
H
H
Sitte
H H
HH
Singer
E A
EA
D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002352:Carrier Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D009479:Neuropeptides; D018377:Neurotransmitter Agents / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D050484:Norepinephrine Plasma Membrane Transport Proteins; D010477:Perfusion; D027981:Symporters; D014162:Transfection; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins
D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D050484:Norepinephrine Plasma Membrane Transport Proteins; C493227:SLC6A2 protein, human; D027981:Symporters; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins; D000661:Amphetamine; D009638:Norepinephrine