CHARACTERIZATION OF [H-3]NISOXETINE BINDING IN RAT VAS-DEFERENS MEMBRANES - MODULATION BY SIGMA-LIGANDS AND PCP-LIGANDS

Sigma (sigma) and phencyclidine (PCP) receptor ligands, apart from the ir main effects on sigma receptors and NMDA receptor-mediated neurotra nsmission, have been found to interact with catecholamine systems in s everal central and peripheral tissues. In the present study the bindin g profile of [H-3]nisoxetine ([H-3]NIS), a selective marker of the nor adrenaline transporter, has been characterized in rat vas deferens mem branes to further study its modulation by a number of characteristic s igma and PCP ligands. The binding of [H-3]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 max imal binding capacity was 1,625 +/- 500 fmol/mg of protein. Kinetic ex periments gave a k(+1) of 3.9.10(7) min(-1)M(-1) and a k(-1) of 0.005 min(-1). The [H-3]NIS binding was totally inhibited, with IC50 values in the micromolar range, by all the sigma and PCP ligands tested, with the following order of potency: haloperidol > dextromethorphan > dizo cilpine > dextrorphan > (+)-3-PPP > PCP > tenocyclidine. This order co rrelates well with that described in other tissues using [H-3]desmethy limipramine. The inhibition by all these compounds, except that of (+) -3-PPP, was competitive. These results suggest that sigma and PCP liga nds bind, at low micromolar concentrations, to a site in the noradrena line transporter that is labelled by [H-3]NIS.