Kinetic mechanism of dopamine transporter interaction with 1-(2-(bis-(4-fluorophenyl)methoxy)ethyl)-4-(3-phenylpropyl)piperazine (GBR 12909)

Interaction of piperazine-based dopamine transporter inhibitor GBR12909 with rat dopamine transporters has been Studied by means of competition kinetics analysis, employing [(3)H]PE21 as the reporter ligand. It has been found that GBR12909 is capable of inducing so-called "slow isomerization step" upon binding to DAT, probably consisting of a conformational change in the transporter protein. The mechanism exhibited by GBR12909 appears to be similar to the mechanism ofPE21 that has been reported earlier and also confirms previous observations for GBR12783 made by Do-Rego and co-workers using dopamine uptake data. it appears that the isomerization phenomenon previously described for PE21 is not limited to tropane-based DAT inhibitors, but is,in fact,a general property of dopamine transporterprotein, similar to "isomerization" process reported previously for G-protein Coupled receptors. The rapid first step of association of the GBR 12909 is characterized by the equilibrium constant K(L) = 34 +/- 11 nM and the second slow step by k(i) = 0.033 +/- 0.005 s(-1). (C) 2008 Elsevier Ltd. All rights reserved.