Mercuric chloride and p-chloromercuriphenylsulfonate exert a biphasic effect on the binding of the stimulant [3H]methylphenidate to the dopamine transporter.
Mercuric chloride was found to have a biphasic effect on the binding of the radiolabeled stimulant [3H]methylphenidate to membranes from a crude synaptosomal preparation of rat striatal tissue. Binding was enhanced at low concentrations of HgCl2, reaching a maximum of 62% above control values at 2.5 microM HgCl2. It was inhibited in a dose-dependent manner at concentrations greater than 5 microM HgCl2, with an IC50 of 7.2 microM. The increase in binding observed at the low concentrations of HgCl2 was shown by Scatchard analysis to be due to an increase in the affinity of [3H]methylphenidate for its binding site on the dopamine transporter, while a decrease in both affinity and Bmax accompanied the reduction of [3H]methylphenidate binding observed at the higher concentrations of the inorganic mercury compound. The sodium salt of the organic mercurial p-chloromercuriphenylsulfonic acid also caused an increase in [3H]methylphenidate binding (159% above controls at 2,000 microM), followed by an immediate decrease in binding at higher concentrations of the reagent. Because both of these mercury-containing compounds have a high propensity for interacting with sulfhydryl groups, these data suggest that the cysteine residues in the dopamine transporter molecule may play an important role in the regulation of stimulant binding to the uptake complex.
Schweri
M M
MM
Division of Basic Medical Sciences, Mercer University School of Medicine, Macon, Georgia 31207-0001.
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins; D004305:Dose-Response Relationship, Drug; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008627:Mercuric Chloride / Q000494:pharmacology*; D008774:Methylphenidate / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000378:metabolism; D014316:Tritium
D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D014316:Tritium; D008774:Methylphenidate; D008627:Mercuric Chloride; D002731:4-Chloromercuribenzenesulfonate; D004298:Dopamine