Selective Transport of Monoamine Neurotransmitters by Human Plasma Membrane Monoamine Transporter and Organic Cation Transporter 3

Abstract

The plasma membrane monoamine transporter (PMAT) and organic cation transporter 3 (OCT3) are the two most prominent low-affinity, high-capacity (i.e., uptake 2 ) transporters for endogenous biogenic amines. Using the Flp-in system, we expressed human PMAT (hPMAT) and human OCT3 (hOCT3) at similar levels in human embryonic kidney 293 cells. Parallel and detailed kinetics analysis revealed distinct and seemingly complementary patterns for the two transporters in transporting monoamine neurotransmitters. hPMAT is highly selective toward serotonin (5-HT) and dopamine, with the rank order of transport efficiency (V max /K m ) being: dopamine, 5-HT Ͼ Ͼ histamine, norepinephrine, epinephrine. The substrate preference of hPMAT toward these amines is substantially driven by large (up to 15-fold) distinctions in its apparent binding affinities (K m ). In contrast, hOCT3 is less selective than hPMAT toward the monoamines, and the V max /K m rank order for hOCT3 is: histamine Ͼ norepinephrine, epinephrine Ͼ dopamine Ͼ5-HT. It is noteworthy that hOCT3 demonstrated comparable (Յ2-fold difference) K m toward all amines, and distinctions in V max played an important role in determining its differential transport efficiency toward the monoamines. Real-time reverse transcription-polymerase chain reaction revealed that hPMAT is expressed at much higher levels than hOCT3 in most human brain areas, whereas hOCT3 is selectively and highly expressed in adrenal gland and skeletal muscle. Our results suggest that hOCT3 represents a major uptake 2 transporter for histamine, epinephrine, and norepinephrine. hPMAT, on the other hand, is a major uptake 2 transporter for 5-HT and dopamine and may play a more important role in transporting these two neurotransmitters in the central nervous system.

Transport of Biogenic Amine Neurotransmitters at the Mouse Blood–Retina and Blood–Brain Barriers by Uptake1 and Uptake2

“…Few in vivo studies have investigated the presence and role of biogenic amines transporters in clearance and dissipation at the abluminal BBB. Pmat could be involved in the clearance and dissipation of dopamine and serotonin at the abluminal/nervous side of the BBB in addition to its role in their neuronal transport (Dahlin et al, 2007;Duan and Wang, 2010;Okura et al, 2011). But, we could not show either Oct3 or Pmat in endothelial cells by immunostaining or luminal transport experiments.…”

“…We first tested for functional biogenic amine transporters at the BBB and BRB using [ 3 H]-MPP + , one of the highest capacity substrates known for Net, Dat, Sert, Oct1-3, Mate1, and Pmat (Amphoux et al, 2006;Buck and Amara, 1994;Duan and Wang, 2010;Koepsell et al, 2007).…”

“…By contrast, carnitine, the amphoteric nutrient substrate of Octn transporters did not modulate the transport of [ 3 H]-MPP + whereas choline only slightly reduced 1.3-fold (P < 0.05) the eye transport ( Figure 3B, solid bars). None of these pharmacologic transport inhibitors affected the luminal transport of [ 3 H]-MPP + at the Swiss mouse BBB ( Figure 3B, H]-dopamine (Dat < Net; Oct1 < < Oct2 < Oct3; Pmat substrate) were measured after in situ carotid perfusion for 60 seconds (Amphoux et al, 2006;Duan and Wang, 2010;Eisenhofer, 2001; Figure 4) Figure 4A) was not inhibited by 1 or 10 mmol/L unlabeled histamine in Swiss mouse and was unchanged in Oct1,2(À/À) Fvb mice ( Figure 4A), suggesting that its membrane permeability does not significantly involve the histamine transporters Oct2 and Oct3 in the Swiss and Fvb mice. The retinal transport of [ 3 H]-serotonin (K in,eye B0.5 mL/s per gram; Figure 4B) was not inhibited by 5 mmol/L L-tryptophan, 10 mmol/L serotonin or Na + /Cl À depletion, and unchanged in Oct1,2(À/À) mice ( Figure 4B, solid bars).…”

“…More recently, uptake2 transporters that are lower affinity, polyspecific and Na + /Cl À -independent have been shown to transport some biogenic amine neurotransmitters and xenobiotics in both directions, depending on their concentration gradient. The best known are Oct1-3 (Slc22a1-3) and Pmat (Slc29a4) (Eisenhofer, 2001;Dahlin et al, 2007;Duan and Wang, 2010). We have examined the possibility that the trafficking of biogenic amine neurotransmitters is not restricted to neurons but may also occur at the bloodnerve barriers as is suggested for some peripheral tissues (Catravas and Gillis, 1983;Chemuturi and Donovan, 2007;Eisenhofer, 2001;Ramamoorthy et al, 1993).…”

Impaired Monoamine and Organic Cation Uptake in Choroid Plexus in Mice with Targeted Disruption of the Plasma Membrane Monoamine Transporter (Slc29a4) Gene

“…Prototype PMAT substrates include biogenic amines, MPP ϩ and MPP ϩ -like neurotoxins, and clinically used drugs (20 -22). Abundantly expressed in multiple brain regions, PMAT represents a major uptake 2 transporter for serotonin (5-HT) and dopamine in the CNS (22). Previous work by Vialou et al (23) and by us (24) showed that PMAT mRNA is highly expressed in mouse and rat CPs.…”