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Characterization of [<sup>3</sup>H]nisoxetine binding in rat vas deferens membranes: Modulation by sigma and PCP ligands

Abstract:

Sigma (σ) and phencyclidine (PCP) receptor ligands, apart from their main effects on σ receptors and NMDA receptor-mediated neurotransmission, have been found to interact with catecholamine systems in several central and peripheral tissues. In the present study the binding profile of [3H]nisoxetine ([3H]NIS), a selective marker of the noradrenaline transporter, has been characterized in rat vas deferens membranes to further study its modulation by a number of characteristic σ and PCP ligands. The binding of [3H]NIS was found to be of high affinity (K(d) = 1.63 ± 0.36 nM), saturable, sodium-dependent and to a single population of binding sites (n(H) = 1.003 ± 0.017). The maximal binding capacity was 1,625 ± 500 fmol/mg of protein. Kinetic experiments gave a k(+1) of 3.9 · 107 min-1 M-1 and a k1 of 0.005 min-1. The [3H]NIS binding was totally inhibited, with IC50 values in the micromolar range, by all the σ and PCP ligands tested, with the following order of potency: haloperidol > dextromethorphan > dizocilpine > dextrorphan > (+)-3-PPP > PCP > tenocyclidine. This order correlates well with that described in other tissues using [3]desmethylimipramine. The inhibition by all these compounds, except that of (±)-3-PPP, was competitive. These results suggest that σ and PCP ligands bind, at low micromolar concentrations, to a site in the noradrenaline transporter that is labelled by [3H]NIS.