Abstract
The aims of this study were to characterize the recently cloned rat norepinephrine transporter (NET) in more detail and in particular to study possible species differences in its pharmacological properties compared with the human and bovine NETs. The study was carried out by measuring the uptake of [3H]norepinephrine in COS-7 cells expressing the NET after transient transfection with rat, human, or bovine NET cDNA. There were small but significant differences between the rat NET and the human or bovine NETs with respect to the affinities of sodium ions (greater for rat than for bovine) of the substrates norepinephrine, epinephrine, and 1-methyl-4-phenylpyridinium (greater for human than for rat), and of the inhibitor cocaine (greater for human and bovine than for rat), whereas the affinities of dopamine and of most inhibitors, including tricyclic antidepressants, showed no species differences. The fact that the affinities for some substrates, cocaine and sodium ions exhibited small but significant interspecies differences among the rat, human, and bovine NETs suggests that ligand recognition, the translocation process, and sodium ion dependence are influenced differentially by just a few amino acid exchanges in the primary sequences of the transporters. On the other hand, the lack of any major differences in the pharmacological properties of the rat, human, and bovine NETs in this study suggests that data obtained in previous studies on rat tissues and bovine cells can be extrapolated, in all except the most quantitative analyses, to the properties of the human NET.
Footnotes
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Send reprint requests to: Dr. Lesley J. Bryan-Lluka, Department of Physiology and Pharmacology, The University of Queensland, Brisbane, Queensland 4072, Australia. E-mail:Lluka{at}plpk.uq.edu.au
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↵1 This study was supported by grants from the National Health and Medical Research Council of Australia and the University of Queensland Round Three Quality Funds for International Research (L.J.B.-L.) and by Deutsche Forschungsgemeinschaft Grant SFB 400 A1 (H.B.). P.P. was a recipient of a graduate training fellowship from the Deutsche Forschungsgemeinschaft (Graduiertenkolleg 246). Preliminary results of this study were presented at the fall meeting of the German Society for Experimental and Clinical Pharmacology and Toxicology (Pörzgen et al., 1997) and the December 1997 meeting of the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists (Paczkowski et al., 1997).
- Abbreviations:
- NET
- norepinephrine transporter
- DAT
- dopamine transporter
- DMEM
- Dulbecco’s modified Eagle’s medium
- GBR 12909
- 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3-phenylpropyl]piperazine dihydrochloride
- MPP+
- 1-methyl-4-phenylpyridinium ion
- SERT
- serotonin (5-hydroxytryptamine) transporter
- TMD
- transmembrane spanning domain
- U-0521
- 3′,4′-dihydroxy-2-methylpropiophenone
- Received December 24, 1998.
- Accepted April 7, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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