Fluctuation of the dopamine uptake inhibition potency of cocaine, but not amphetamine, at mammalian cells expressing the dopamine transporter

Abstract

Cocaine, amphetamines and other psychostimulants inhibit synaptic dopamine uptake by interfering with dopamine transporter (DAT) function. The resultant potentiation of dopaminergic neurotransmission is associated with psychostimulant addiction. Fluctuations in dopamine uptake inhibition potency (DUIP) were observed for classical DAT blockers including cocaine, mazindol, methylphenidate (Ritalin™) and benztropine in CHO cells expressing wildtype DAT; cocaine potency also decreased in DAT-expressing non-neuronal COS-7 cells and neuronal N2A neuroblastoma cells. In contrast, the DAT substrate (+)-amphetamine did not display this DUIP fluctuation. In parallel experiments, no fluctuation was observed for the apparent binding affinities of these 5 drugs. The DUIP decrease appeared to correlate with an increase in cell surface DAT expression level, as measured by B max values and confocal microscopy. The fact that the DUIP profile of amphetamine diverged from that of the classical DAT blockers is consistent with the idea of fundamental differences between the mechanisms of abused psychostimulant DAT substrates and inhibitors. Identification of the cellular factors that underlie the DAT inhibitor DUIP fluctuation phenomenon may be relevant to anti-psychostimulant drug discovery efforts.

Site-Directed Mutations near Transmembrane Domain 1 Alter Conformation and Function of Norepinephrine and Dopamine Transporters

“…This could be attributed to differences in assay conditions and cell lines (Han and Gu, 2006). Passage number and expression level in transfected cells caused variability in the inhibition potency of cocaine for DA uptake (Chen and Reith, 2007;Ukairo et al, 2007). (Tables 3 and 4) were comparable with values reported previously (Reith et al, 2005), possibly because of the similarity of the assay conditions and reagents used.…”

Cocaine self-administration reinforced on a progressive ratio schedule decreases with continuous d-amphetamine treatment in rats

“…Further work is necessary to distinguish between the contribution of a learned component versus other pharmacological interactions that might occur with simultaneous cocaine and d- amphetamine administration (see Jayanthi and Ramamoorthy 2005; Scarponi et al 1999; Ukairo et al 2007). Whatever the mechanism, cocaine self-administration was shown here to be suppressed for up to 14 days after mini-pump removal.…”

3,4-Methylenedioxy-N-methamphetamine (ecstasy) promotes the survival of fetal dopamine neurons in culture

“…Amphetamine has been shown in some studies to increase surface expression of DAT on DA neurons (Ukairo et al, 2007) while some suggest the opposite (Sulzer et al, 2005; Wei et al, 2007). However, these findings are postulated to be a result of translocation of DAT between the cytosol and the membrane rather than a result of changes in gene expression (Ukairo et al, 2007). While we need to confirm that these changes in slc6a3 expression translate into greater expression of DAT protein, understanding why MDMA’s occupancy of DAT results in increased gene expression for DAT, and how this enhances DA neuron survival is a key goal of future studies.…”