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PubMed1993

Blockade by newly-developed antidepressants of biogenic amine uptake into rat brain synaptosomes.

We determined the uptake blockade produced by eight new antidepressant drugs (etoperidone, femoxetine, lofepramine, nefazodone, paroxetine, sertraline, tomoxetine, and venlafaxine), two metabolites of newer antidepressants (desmethylsertraline and norfluoxetine), seven previously reported antidepressants, and carbamazepine. Inhibitor constants (Kis) for uptake blockade were obtained from competitive uptake studies with [3H]norepinephrine, [3H]5-hydroxytryptamine, and [3H]dopamine in rat brain synaptosomes prepared from hippocampus, frontal cortex, and striatum, respectively. Among the newer compounds, tomoxetine (Ki = 0.7 nM) and lofepramine (Ki = 1.9 nM) were potent and selective [3H]norepinephrine uptake blockers; paroxetine (Ki = 0.73 nM), sertraline (Ki = 3.4 nM), and femoxetine (Ki = 22 nM) potently and selectively inhibited [3H]5-hydroxytryptamine uptake. Although none of the drugs was potent for [3H]dopamine uptake blockade, sertraline was the most potent (Ki = 260 nM). These data are useful in predicting adverse effects and drug-drug interactions of antidepressants.

Animals↗
PubMed1993

Studies of the biogenic amine transporters. II. A brief study on the use of [3H]DA-uptake-inhibition to transporter-binding-inhibition ratios for the in vitro evaluation of putative cocaine antagonists.

The cocaine receptor on the dopamine transporter is a logical target binding site for the design and synthesis of novel agents for evaluation as possible cocaine antagonists. Although there is no widely accepted and validated assay for detecting a cocaine antagonist, one commonly accepted strategy is to compare the IC50 value of a test agent for inhibition of [3H]dopamine uptake and its IC50 value for inhibition of the binding of a transporter ligand such as [125I]RTI-55. The goal of such a comparison is to guide the synthesis of agents which have high "uptake-to-binding ratios", i.e. agents which are much more potent in the binding assay than they are in the uptake assay. In the present study we tested the hypothesis that ratios different from unity can result from the fact that the two assays are conducted under markedly different conditions. The results showed that conducting the uptake and binding assays under identical conditions reduced the GBR12935 uptake-to-binding ratio of 6.20 (under standard assay conditions) to 0.36. These data indicate that uptake-to-binding ratios must be interpreted with caution, and emphasizes the need for simpler and less expensive methods than cocaine self-administration paradigms to screen compounds as modulators of cocaine reinforcement.

Animals↗