RGD Reference Report - Activation of the extraneuronal monoamine transporter (EMT) from rat expressed in 293 cells. - Rat Genome Database

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Activation of the extraneuronal monoamine transporter (EMT) from rat expressed in 293 cells.

Authors: Grundemann, D  Koschker, AC  Haag, C  Honold, C  Zimmermann, T  Schomig, E 
Citation: Grundemann D, etal., Br J Pharmacol. 2002 Nov;137(6):910-8.
RGD ID: 1643218
Pubmed: PMID:12411423   (View Abstract at PubMed)
PMCID: PMC1573551   (View Article at PubMed Central)
DOI: DOI:10.1038/sj.bjp.0704926   (Journal Full-text)

1. The extraneuronal monoamine transporter from rat (EMTr) was heterologously expressed by stable transfection in human embryonic kidney 293 cells and characterized in radiotracer experiments. 2. EMTr-mediated uptake of 1-methyl-4-phenylpyridinium (MPP(+)) was saturable, with a K(m) of 151 micro mol l(-1) and V(max) of 7.5 nmol min(-1) mg protein(-1). 3. Compared to the human orthologue EMTh (gene symbol SLC22A3), EMTr was about two orders of magnitude more resistant to most inhibitors, including disprocynium24 and corticosterone. 4. Strikingly, inhibitors and substrates at low concentration stimulated EMTr-mediated transport above control level with MPP(+) and noradrenaline as substrate, but not with cimetidine. Results were confirmed with EMT from mouse. 5. With different IC(50)-values for different substrates, the standard method to calculate K(i)-values is not applicable. 6. Our experiments suggest that activation is not caused by changes in membrane potential or trans-stimulation. Since the extent of activation depends markedly on the chemical structure of the monitored substrate, involvement of a receptor-mediated signalling pathway or recruitment of transporter reserve are implausible. 7. To explain activation, we present a kinetic model which assumes two binding sites for substrate or inhibitor per transporter entity, possibly resulting from the assembly of homodimers. 8. Activation explains previous reports about inhibitor-insensitive catecholamine transport in rat brain. 9. We speculate that activation may serve to keep the transporter working for specific substrates in the face of inhibitors.

Gene Ontology Annotations    Click to see Annotation Detail View

Biological Process
TermQualifierEvidenceWithReferenceNotesSourceOriginal Reference(s)
organic cation transport  IDA 1643218neurotoxin 1-methyl-4-phenylpyridinium RGD 

Molecular Function
TermQualifierEvidenceWithReferenceNotesSourceOriginal Reference(s)
toxin transmembrane transporter activity  IDA 1643218neurotoxin 1-methyl-4-phenylpyridinium RGD 

Objects Annotated

Genes (Rattus norvegicus)
Slc22a3  (solute carrier family 22 member 3)


Additional Information