Uniporter
[6] Voltage-gated potassium channels are also uniporters found in neurons and are essential for action potentials.
They help to bring glucose from the blood or extracellular space into cells usually to be utilized for metabolic processes in generating energy.
[9] Uniporters are essential for certain physiological processes in cells, such as nutrient uptake, waste removal, and maintenance of ionic balance.
Early research in the 19th and 20th centuries on osmosis and diffusion provided the foundation for understanding the passive movement of molecules across cell membranes.
[11] Through the work of Charles Overton in the 1890s, the concept that the biological membrane is semipermeable became important to understanding the regulation of substances in and out of the cells.
[11] The discovery of facilitated diffusion by Wittenberg and Scholander suggested that proteins in the cell membrane aid in the transport of molecules.
[14] Newer research is focusing on techniques using recombinant DNA technology, electrophysiology and advanced imaging to understand uniporter functions.
These experiments are designed to clone and express transporter genes in host cells to further analyze the three-dimensional structure of uniporters, as well as directly observe the movement of ions through proteins in real-time.
[16] The GLUT proteins are encoded by the SLC2 genes and categorized into three classes based on amino acid sequence similarity.
[16] GLUT1 is found in various tissues like the red blood cells, brain, and blood-brain barrier and is responsible for basal glucose uptake.
[16] Class III includes GLUT5, found in the small intestine, kidney, testes, and skeletal muscle.
[22] The transporter is of particular significance in the central nervous system as it provides the necessary amino acids for protein synthesis and neurotransmitter production in brain cells.
[22] Aromatic amino acids like phenylalanine and tryptophan are precursors for neurotransmitters like dopamine, serotonin, and norepinephrine.
[25] Nucleosides serve as building blocks for nucleic acid synthesis and are key components for energy metabolism in creating ATP/ GTP.
They also have the ability to deliver nucleoside analogs to intracellular targets for the treatment of tumors and viral infections.
[26] ENTs are part of the Major Facilitator Superfamily (MFS) and are suggested to transport nucleosides using a clamp-and-switch model.
[26] In this model, the substrate first binds to the transporter, which leads to a conformational change that forms an occluded state (clamp).
[25] hENT2 is expressed mostly in neurological tissues and small parts of the skin, placenta, urinary bladder, heart muscle and gallbladder.
Upon binding and recognition of a specific substrate molecule on one side of the uniporter membrane, a conformational change is triggered in the transporter protein.
[27] Unlike symporters and antiporters, uniporters transport one molecule/ion in a single direction based on the concentration gradient.
[28] The entire process depends on the substrate's concentration difference across the membrane to be the driving force for the transport by uniporters.
