Hydrogen ion concentration differentiates effects of methamphetamine and dopamine on transporter-mediated efflux.
Methamphetamine (METH) causes release of stored intracellular dopamine (DA). We explored the interactions of METH with the recombinant human vesicular monoamine (hVMAT2) and/or human DA transporters (hDAT) in transfected mammalian (HEK293) cells and compared the findings with those for DA. In 'static' release assays at 37 degrees C, less than 20% of pre-loaded [(3)H]DA was lost after 60 min, while nearly 80% of pre-loaded [(3)H]METH was lost at 37 degrees C under non-stimulated conditions. Results obtained by measuring substrate release using a superfusion apparatus revealed an even greater difference in substrate efflux. At pH 7.4, nearly all of the pre-loaded [(3)H]METH was lost after just 6 min, compared with the loss of 70-80% of pre-loaded [(3)H]DA (depending on cell type) after superfusion for 32 min. Increasing the extracellular pH from 7.4 to 8.6 had opposite effects on [(3)H]DA and [(3)H]METH retention. At pH 8.6, [(3)H]METH was retained more effectively by both hDAT and hDAT-hVMAT2 cells, compared with results obtained at extracellular pH 7.4. [(3)H]DA, however, was more effectively retained at pH 7.4 than at pH 8.6. These data suggest that DA and METH interact differently with the DAT and VMAT2, and require different H(+) concentrations to exert their effects.
Wilhelm
Clare J
CJ
Veteran Affairs Medical Center, Oregon Health and Science University, Portland, Oregon 97239, USA.
Johnson
Robert A
RA
Eshleman
Amy J
AJ
Janowsky
Aaron
A
D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D004298:Dopamine / Q000378:metabolism / Q000494:pharmacology*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008694:Methamphetamine / Q000378:metabolism / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D050493:Vesicular Monoamine Transport Proteins / Q000235:genetics / Q000378:metabolism
D050483:Dopamine Plasma Membrane Transport Proteins; D011994:Recombinant Proteins; C493452:SLC18A2 protein, human; D050493:Vesicular Monoamine Transport Proteins; D008694:Methamphetamine; D004298:Dopamine