Inhibition of striatal dopamine transporter activity by 17beta-estradiol.
Female; Animals; Rats; Dopamine/metabolism; Neostriatum/*drug effects/metabolism; Dopamine Plasma Membrane Transport Proteins; *Membrane Glycoproteins; *Nerve Tissue Proteins; Estradiol/*pharmacology; *Membrane Transport Proteins; Carrier Proteins/*antagonists & inhibitors; Synaptosomes/*drug effects/metabolism; Sprague-Dawley
Striatal synaptosomes from ovariectomized rats were prepared to examine the effect of 17beta-estradiol on [3H]dopamine uptake. Estradiol inhibited [3H]dopamine uptake in a dose-dependent manner, with an IC50 of 7.2 microM. Use of identical concentrations of progesterone had no effect on [3H]dopamine uptake. The effects of estradiol were exerted by decreasing the affinity of the transporter for dopamine, as revealed by a dose-dependent increase in the Km. The Km values for 0 (control), 10, and 100 microM estradiol were 108+/-11 258+/-44 and 415+/-40 nM, respectively, with each of the three concentrations tested being significantly different among each other. No statistically significant differences were obtained for the Vmax, with values for the three increasing doses being 9.2+/-0.8, 8.3+/-0.5 and 7.3+/-0.8 pmol/min per mg protein. These results demonstrate that estradiol, but not progesterone, inhibits striatal dopamine uptake by decreasing the affinity of the transporter for dopamine. Such a mechanism may serve as one of the bases for the modulatory effects of estradiol upon the nigrostriatal dopaminergic system.
Disshon K A; Boja J W; Dluzen D E
European journal of pharmacology
1998
1998-03
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Multiple binding sites for [125I]RTI-121 and other cocaine analogs in rat frontal cerebral cortex.
*Membrane Transport Proteins; *Nerve Tissue Proteins; *Symporters; Animals; Binding; Binding Sites; Carrier Proteins/*metabolism; Cocaine/*analogs & derivatives/pharmacokinetics; Competitive; Corpus Striatum/*metabolism; Dopamine Plasma Membrane Transport Proteins; Dopamine/metabolism; Frontal Lobe/*metabolism; Iodine Radioisotopes/*pharmacokinetics; Kinetics; Male; Membrane Glycoproteins/*metabolism; Norepinephrine Plasma Membrane Transport Proteins; Norepinephrine/metabolism; Rats; Regression Analysis; Serotonin Plasma Membrane Transport Proteins; Serotonin/metabolism; Sprague-Dawley
In an effort to identify novel binding sites for cocaine and its analogs, we carried out binding studies with the high-affinity and selective ligand [125I]RTI-121 in rat frontal cortical tissue. Very low densities of binding sites were found. Saturation analysis revealed that the binding was to both high- and low-affinity sites. Pharmacological competition studies were carried out with inhibitors of the dopamine, norepinephrine, and serotonin transporters. The various transporter inhibitors inhibited the binding of 15 pM [125I]RTI-121 in a biphasic fashion following a two-site binding model. The resultant data were complex and did not suggest a simple association with any single transporter. Correlational analysis supported the following hypothesis: [125I] RTI-121 binds to known transporters and not to novel sites; these include dopamine, norepinephrine, and serotonin transporters. Immunoprecipitation of transporters photoaffinity labeled with [125]RTI-82 and subsequent analysis of SDS-page gels revealed the presence of authentic dopamine transporters in these samples; displacement of the photoaffinity label occurred with a typical dopamine transporter pharmacology. These data are compatible with the binding properties of RTI-121 and the presence of several known transporters in the tissue studied.
Boja J W; Carroll F I; Vaughan R A; Kopajtic T; Kuhar M J
Synapse (New York, N.Y.)
1998
1998-09
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1002/(SICI)1098-2396(199809)30:1%3C9::AID-SYN2%3E3.0.CO;2-7" target="_blank" rel="noreferrer noopener">10.1002/(SICI)1098-2396(199809)30:1%3C9::AID-SYN2%3E3.0.CO;2-7</a>