Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.64 (MPP)
 1,876 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recently, another research group has reported an almost complete loss of function of the human norepinephrine transporter (hNET) in patients who had orthostatic intolerance and who were heterozygous for a guanine to cytosine exchange, resulting in a hNET Ala(457)Pro variant. To explore the reason for the deficiency in NET function, we compared in detail the pharmacology of the Ala(457)Pro variant with that of the wild-type hNET in COS-7 cells transiently transfected with hNET or Ala(457)Pro cDNA. Compared to the wild-type hNET, the Ala(457)Pro variant exhibited a five-fold higher affinity for cocaine, but a two-fold lower affinity for the NET inhibitor nisoxetine, and an unchanged affinity for the antidepressant desipramine. Plasma membrane expression (measured as Bmax of [3H]nisoxetine binding) of the Ala(457)Pro variant was only 40% of that of the wild-type hNET. The Ala(457)Pro variant showed a six- to 10-fold decrease in affinity for the substrates dopamine and 1-methyl-4-phenylpyridinium (MPP(+)). Compared with the wild-type hNET, the maximum rate (V(max)) of norepinephrine uptake by the Ala(457)Pro variant was slightly reduced, whereas the turnover number (calculated from V(max)/B(max)) was approximately two-fold higher. However, the Ala(457)Pro variant exhibited a 50-fold higher K(m) (i.e. lower apparent affinity) for norepinephrine than the wild-type hNET. Thus, the previously reported loss of function of the Ala(457)Pro variant associated with orthostatic intolerance is only partly due to a reduction in plasma membrane expression of the transporter, and is mainly caused by the pronounced reduction in the apparent affinity of norepinephrine.
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PMID:Pharmacological properties of the naturally occurring Ala(457)Pro variant of the human norepinephrine transporter. 1187 70

Synthetic cathinone derivatives are a new class of psychoactive substances (NPS), also known as "bath salts", designed to exert psychostimulant effects resembling those of well-known psychostimulants, such as cocaine and 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"). As major constituents of bath salts, the cathinone derivatives 3,4-methylenedioxypyrovalerone (MDPV) and 4-methylmethcathinone (mephedrone), have received considerable media attention. MDPV and mephedrone interfere with the function of the high affinity transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT), resulting in increased extracellular levels of these monoamines, though their mechanism of action differs. MDPV acts as a non-transported inhibitor of DAT, NET and SERT, whereas mephedrone promotes transporter-mediated release in an amphetamine-like fashion. MDPV and mephedrone are often taken together, creating a conundrum in as much as non-transported inhibitors, like MDPV, prevent mephedrone-induced reverse transport via DAT, NET and SERT. Here we provide evidence supporting a role for organic cation transporter 3 (OCT3) in the actions of mephedrone, which may account for its ability to enhance effects of MDPV. We show that mephedrone can induce substrate efflux via OCT3 in the presence of MDPV. Real-time recordings of the fluorescent OCT3 substrate (4-(4-dimethylamino)styryl)-N-methylpyridinium (ASP+) and radiotracer-flux studies using [3H]1-methyl-4-phenyl-pyridinium (MPP+), demonstrated that OCT3 is MDPV-insensitive when expressed in human embryonic kidney (HEK293) cells. Ex vivo experiments performed in cultured superior cervical ganglia (SCG) cells, rich in NET and OCT3, revealed that mephedrone induces [3H]MPP+ release in an OCT3-dependent manner when NET is fully occupied with MDPV. These results extend our recent findings that OCT3 is key in the mechanism of action of amphetamine-induced substrate release. OCT3 likewise appears to be a mechanism through which mephedrone can induce release of monoamines, thereby accounting for the paradoxically more potent psychostimulant effects of MDPV taken together with mephedrone, and greater risk for deleterious side effects.
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PMID:"Polytox" synthetic cathinone abuse: A potential role for organic cation transporter 3 in combined cathinone-induced efflux. 3024 32