9704886

pubmed:Citation

1

Drug-induced efflux of substrates was characterized in C6 rat glioma cells stably expressing a recombinant human dopamine (DA) or serotonin (5-HT) transporter (C6-hDAT and C6-hSERT, respectively). In the absence of Ca2+, these cells spontaneously and rapidly released preloaded [3H]DA or [3H]5-HT, respectively, but maintained constant levels of [3H]N-methy-4-phenylpyridinium (MPP+) for up to 90 minutes. In C6-hSERT cells, transporter substrates such as methamphetamine, amphetamine, and dopamine induced relatively rapid release of [3H]MPP+, with t1/2 values of approximately 15 minutes, while the t1/2 value for serotonin was about 30 minutes. Similar results were obtained with C6-hDAT cells. Uptake blockers that are not substrates at the transporters had considerably greater t1/2 values, as compared to substrates, suggesting different mechanisms for altering transporter function. Dose-response curves for each drug, conducted at each drug's t1/2, indicated considerable differences in potency (EC50) at stimulating [3H]MPP+ release from C6-hSERT cells [3beta-(4-iodophenyl)tropane-2beta-carboxylic acid methyl ester (RTI-55) > imipramine > 1-[2-diphenylmethoxy]ethyl-4-(3-phenylpropyl)-piperazine (GBR-12935) threo-(+/-)-methylphenidate > cocaine > mazindol > 2-beta-carbomethoxy-3beta-(4-fluorophenyl)tropane (CFT) > (+)methamphetamine > amphetamine > DA > fenfluramine > norepinephrine (NE) > 5-HT]. A different rank order of potency was observed for the effects of drugs on [3H]MPP+ release from C6-hDAT cells [imipramine > RTI-55 > cocaine > mazindol > CFT > GBR-12935 > threo-(+/-)-methylphenidate > amphetamine > (+)methamphetamine > fenfluramine > DA > NE > 5-HT]. Based on efficacies for stimulating [3H]MPP+ release from C6-hDAT cells, drugs could be grouped into three categories, with substrates causing release of approximately 75% of loaded [3H]MPP+, cocaine analogues causing approximately 50% release, and other drugs causing an average release of approximately 25% of loaded [3H]MPP+. The results, taken together with results from previous reports, suggest that the transfected cell type contributes to the characteristics of transporter-mediated release, that drugs interact with different sites on the transporters in the uptake and release process, and that the mechanism of transporter-mediated release may not be a simple reversal of substrate uptake.

eng

IM

MEDLINE

0887-4476

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NLM

97-106

pubmed-meshheading:9704886-1-Methyl-4-phenylpyridinium, pubmed-meshheading:9704886-Animals, pubmed-meshheading:9704886-Biological Transport, pubmed-meshheading:9704886-Calcium, pubmed-meshheading:9704886-Carrier Proteins, pubmed-meshheading:9704886-Cloning, Molecular, pubmed-meshheading:9704886-Cocaine, pubmed-meshheading:9704886-Dopamine, pubmed-meshheading:9704886-Dopamine Plasma Membrane Transport Proteins, pubmed-meshheading:9704886-Dopamine Uptake Inhibitors, pubmed-meshheading:9704886-Glioma, pubmed-meshheading:9704886-Half-Life, pubmed-meshheading:9704886-Humans, pubmed-meshheading:9704886-Imipramine, pubmed-meshheading:9704886-Kinetics, pubmed-meshheading:9704886-Membrane Glycoproteins, pubmed-meshheading:9704886-Membrane Transport Proteins, pubmed-meshheading:9704886-Methamphetamine, pubmed-meshheading:9704886-Nerve Tissue Proteins, pubmed-meshheading:9704886-Rats, pubmed-meshheading:9704886-Recombinant Proteins, pubmed-meshheading:9704886-Serotonin, pubmed-meshheading:9704886-Serotonin Plasma Membrane Transport Proteins, pubmed-meshheading:9704886-Serotonin Uptake Inhibitors, pubmed-meshheading:9704886-Transfection, pubmed-meshheading:9704886-Tritium

[3H]substrate- and cell-specific effects of uptake inhibitors on human dopamine and serotonin transporter-mediated efflux.

Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S.