Plasma membrane monoamine transporter

The plasma membrane monoamine transporter (PMAT) is a low-affinity is_associated_with::monoamine transporter is_associated_with::protein which in humans is encoded by the SLC29A4 is_associated_with::gene. It is known alternatively as the human equilibrative nucleoside transporter-4 (hENT4). Unlike other members of the ENT family, it is impermeable to most is_associated_with::nucleosides, with the exception of the inhibitory neurotransmitter and is_associated_with::ribonucleoside is_associated_with::adenosine, which it is permeable to in a highly pH-dependent manner.

This protein is an integral membrane protein that transports the monoamine neurotransmitters (is_associated_with::serotonin, is_associated_with::dopamine, is_associated_with::norepinephrine) as well as is_associated_with::adenosine, from synaptic spaces into presynaptic neurons or neighboring glial cells. It is abundantly expressed in the human brain, heart tissue, and skeletal muscle, as well as in the kidneys. It is relatively insensitive to the high affinity inhibitors (such as SSRIs) of the SLC6A monoamine transporters (SERT, DAT, NET), as well being only weakly sensitive to the adenosine transport inhibitor, is_associated_with::dipyridamole. Its transport of monoamines, unlike for adenosine, is pH-insensitive. At low pH, (5.5-6.5 range, as occurs under ischemic conditions) however, its transport efficiency for adenosine becomes greater than for serotonin.

It has 530 amino acid residues with 10–12 transmembrane segments, and is not homologous to other known monoamine transporters, such as the high-affinity SERT, DAT, and NET, or the low-affinity SLC22A OCT family. It was initially identified by a search of the draft human genome database by its sequence homology to ENTs (equilibrative nucleoside transporters).

Inhibitors
No highly selective PMAT inhibitors are yet available, but a number of existing compounds have been found to act as weak inhibitors of this transporter, with the exception of is_associated_with::decynium-22, which is more potent. These compounds include:


 * is_associated_with::Cimetidine
 * is_associated_with::Decynium-22
 * is_associated_with::Dipyridamole
 * is_associated_with::Quinidine
 * is_associated_with::Quinine
 * is_associated_with::Tryptamine
 * is_associated_with::Verapamil

Substrates

 * is_associated_with::Acetylcholine (poor)
 * is_associated_with::Adenosine (at low pH)
 * is_associated_with::Dopamine
 * is_associated_with::Epinephrine
 * is_associated_with::Histamine (poor)
 * is_associated_with::Metformin (poor, pH-dependent)
 * is_associated_with::MPP+
 * is_associated_with::Norepinephrine
 * is_associated_with::Serotonin