Carrier‐Mediated Release, Transport Rates, and Charge Transfer Induced by Amphetamine, Tyramine, and Dopamine in Mammalian Cells Transfected with the Human Dopamine Transporter

Abstract

Amphetamine and related substances induce dopamine release. According to a traditional explanation, this dopamine release occurs in exchange for amphetamine by means of the dopamine transporter (DAT). We tested this hypothesis in human embryonic kidney 293 cells stably transfected with the human DAT by measuring the uptake of dopamine, tyramine, and d‐ and l‐amphetamine as well as substrate‐induced release of preloaded N‐methyl‐4‐[3H]phenylpyridinium ([3H]MPP+). The uptake of substrates was sodium‐dependent and was inhibited by ouabain and cocaine, which also prevented substrate‐induced release of MPP+. Patch‐clamp recordings revealed that all four substrates elicited voltage‐dependent inward currents (on top of constitutive leak currents) that were prevented by cocaine. Whereas individual substrates had similar affinities in release, uptake, and patch‐clamp experiments, maximal effects displayed remarkable differences. Hence, maximal effects in release and current induction were ∼25% higher for d‐amphetamine as compared with the other substrates. By contrast, dopamine was the most efficacious substrate in uptake experiments, with its maximal initial uptake rate exceeding those of amphetamine and tyramine by factors of 20 and 4, respectively. Our experiments indicate a poor correlation between substrate‐induced release and the transport of substrates, whereas the ability of substrates to induce currents correlates well with their releasing action.

Tyramine excites rat subthalamic neurons in vitro by a dopamine-dependent mechanism

“…In support of a dopaminergic mechanism, we found that inward currents evoked by tyramine and amphetamine were reduced about 70% by AMPT and reserpine pretreatment. The catecholamine uptake inhibitor nomifensine significantly reduced tyramine-induced inward currents, which is consistent with the hypothesis that tyramine must bind to the dopamine transporter to cause dopamine release (Sitte et al, 1998). Moreover, mediation by noradrenaline is unlikely because we showed that prazosin failed to block tyramine inward currents.…”

“…This structural similarity makes tyramine a good substrate for both the cytoplasmic dopamine transporter (Sitte et al, 1998;Parker and Cubeddu, 1988) and the vesicular monoamine transporter-2 (Partilla et al, 2006). Disruption of these transport mechanisms by tyramine causes release of dopamine into the extracellular space (Vaccari et al, 1991).…”

Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease—resemblance to the effect of amphetamine drugs of abuse

“…Amphetamines increase extraneuronal dopamine and other monoamine levels, through a nonͲexocytotic mechanism, by directly interacting with monoaminergic cells [283,286,287]. Due to its structural similarity with dopamine, amphetamine is a substrate for the DAT [288]and, when in low concentrations,itis transported by the DAT to the cytosol. This leads to an increase in the intracellular binding sites of DAT for dopamine, resulting in the exchange of extracellular amphetamine by intracellular dopamine, and leading to an increase in extracellular dopamine [289].…”

Cellular and molecular mechanisms involved in the neurotoxicity of opioid and psychostimulant drugs

“…Due to its structural similarity with dopamine, amphetamine is a substrate for the dopamine transporter (DAT) (Sitte et al, 1998). At low concentrations, amphetamine is transported by the DAT to the cytosol and increases the intracellular binding sites of the DAT for dopamine, resulting in the exchange of extracellular amphetamine by intracellular dopamine, and leading to an increase in extracellular dopamine (Jones et al, 1999).…”