Characterization of [3H]zetidoline binding to rat striatal membranes

The binding of [3H]zetidoline, a novel neuroleptic agent, to rat brain striatal membranes was investigated in-vitro. The optimal binding conditions for [3H]zetidoline differed from those for [3H]spiperone in pH, temperature and time. [3H]Zetidoline has high affinity for striatal dopamine receptors. Its binding is saturable, stereo-specific, has a low non-specific component and is reversible and tissue specific. The Scatchard analysis gave a biphasic curve, indicating that [3H]zetidoline interacts with more than one population of receptor sites (B'max = 67 fmol mg-1 protein, K'd = 0.11 nM; B"max = 500 fmol mg-1 protein, K'd = 2.49 nM). Kinetic analysis of rates of association and dissociation yielded a Kd value in agreement with that measured at equilibrium. Inhibition studies indicated that only dopamine and dopaminergic agents are able to displace [3H]zetidoline from its binding sites, and in a different rank order from that for displacement of [3H]spiperone. (-)-Sulpiride was especially effective in inhibiting [3H]zetidoline specific binding. Furthermore, like that of [3H]benzamides, [3H]zetidoline binding appears to be highly Na+-dependent and Li+ only partially substitutes Na+.