Sodium dependence of [3H]paroxetine binding and 5-[3H]hydroxytryptamine uptake in rat diencephalon.
The sodium dependence of binding of [3H]-paroxetine, a selective serotonin uptake inhibitor, to the serotonin transporter in rat diencephalon was studied in both brain membranes and tissue sections and compared with that of 5-[3H]hydroxytryptamine ([3H]5-HT) uptake by synaptosomes from the same region. Binding of [3H]-paroxetine in both the membranes and sections displayed clear sodium dependence until a plateau occurring at 60 nM NaCl, the EC50 for sodium being 8 and 25 mM, respectively. The affinity (1/KD) of [3H]paroxetine binding was a simple hyperbolic function of sodium concentration. In contrast, the density of [3H]paroxetine sites was not affected by external Na+ concentration. The uptake of [3H]5-HT showed a similar pattern of sodium dependence with an EC50 for Na+ of 25 mM. Both the affinity (1/Km) and the rate (Vmax) of [3H]5-HT uptake were dependent on external [Na+] with sodium-dependence curves fitting a rectangular hyperbola. The kinetic analysis of results indicates that one sodium ion is required for the binding of [3H]paroxetine as well as for the binding and translocation of each [3H]5-HT molecule. The results concur with a single-site model of the sodium-dependent serotonin transporter with common or overlapping domains for 5-HT and 5-HT uptake inhibitors.
Mann
C D
CD
Department of Pharmacology, Faculty of Medicine, University of Ottawa, Ontario, Canada.
Hrdina
P D
PD
D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D004027:Diencephalon / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D017374:Paroxetine / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000493:pharmacokinetics*; D012964:Sodium / Q000494:pharmacology / Q000502:physiology*; D014316:Tritium
D014316:Tritium; D012701:Serotonin; D017374:Paroxetine; D012964:Sodium