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In cellular biology, active transport is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellular energy to achieve this movement. There are two types of active transport: primary active transport that uses adenosine triphosphate (ATP), and secondary active transport that uses an electrochemical gradient. This process is in contrast to passive transport, which allows molecules or ions to move down their concentration gradient, from an area of high concentration to an area of low concentration, without energy.
Cotransporters are a subcategory of membrane transport proteins (transporters) that couple the favorable movement of one molecule with its concentration gradient and unfavorable movement of another molecule against its concentration gradient. They enable coupled or cotransport and include antiporters and symporters. In general, cotransporters consist of two out of the three classes of integral membrane proteins known as transporters that move molecules and ions across biomembranes. Uniporters are also transporters but move only one type of molecule down its concentration gradient and are not classified as cotransporters.
Cholestasis is a condition where the flow of bile from the liver to the duodenum is impaired. The two basic distinctions are:
Glucose transporters are a wide group of membrane proteins that facilitate the transport of glucose across the plasma membrane, a process known as facilitated diffusion. Because glucose is a vital source of energy for all life, these transporters are present in all phyla. The GLUT or SLC2A family are a protein family that is found in most mammalian cells. 14 GLUTS are encoded by the human genome. GLUT is a type of uniporter transporter protein.
The solute carrier (SLC) group of membrane transport proteins include over 400 members organized into 66 families. Most members of the SLC group are located in the cell membrane. The SLC gene nomenclature system was originally proposed by the HUGO Gene Nomenclature Committee (HGNC) and is the basis for the official HGNC names of the genes that encode these transporters. A more general transmembrane transporter classification can be found in TCDB database.
Sodium-dependent glucose cotransporters are a family of glucose transporter found in the intestinal mucosa (enterocytes) of the small intestine (SGLT1) and the proximal tubule of the nephron. They contribute to renal glucose reabsorption. In the kidneys, 100% of the filtered glucose in the glomerulus has to be reabsorbed along the nephron. If the plasma glucose concentration is too high (hyperglycemia), glucose passes into the urine (glucosuria) because SGLT are saturated with the filtered glucose.
The Na–K–Cl cotransporter (NKCC) is a transport protein that aids in the secondary active transport of sodium, potassium, and chloride into cells. In humans there are two isoforms of this membrane transport protein, NKCC1 and NKCC2, encoded by two different genes. Two isoforms of the NKCC1/Slc12a2 gene result from keeping or skipping exon 21 in the final gene product.
The sodium/phosphate cotransporter is a member of the phosphate:Na+ symporter (PNaS) family within the TOG Superfamily of transport proteins as specified in the Transporter Classification Database (TCDB).
Sodium/glucose cotransporter 1 (SGLT1) also known as solute carrier family 5 member 1 is a protein in humans that is encoded by the SLC5A1 gene which encodes the production of the SGLT1 protein to line the absorptive cells in the small intestine and the epithelial cells of the kidney tubules of the nephron for the purpose of glucose uptake into cells. Recently, it has been seen to have functions that can be considered as promising therapeutic target to treat diabetes and obesity. Through the use of the sodium glucose cotransporter 1 protein, cells are able to obtain glucose which is further utilized to make and store energy for the cell.
Peptide transporter 1 also known as solute carrier family 15 member 1 (SLC15A1) is a protein that in humans is encoded by SLC15A1 gene. PepT 1 is a solute carrier for oligopeptides. It functions in renal oligopeptide reabsorption and in the intestines in a proton dependent way, hence acting like a cotransporter.
Ileal sodium/bile acid cotransporter, also known as apical sodium–bile acid transporter (ASBT) and ileal bile acid transporter (IBAT), is a bile acid:sodium symporter protein that in humans is encoded by the SLC10A2 gene.
Solute carrier organic anion transporter family member 1B3 (SLCO1B3) also known as organic anion-transporting polypeptide 1B3 (OATP1B3) is a protein that in humans is encoded by the SLCO1B3 gene.
Sodium/bile acid cotransporter also known as the Na+-taurocholate cotransporting polypeptide (NTCP) or liver bile acid transporter (LBAT) is a protein that in humans is encoded by the SLC10A1 (solute carrier family 10 member 1) gene.
Sodium-dependent phosphate transport protein 2B (NaPi2b) is a protein that in humans is encoded by the SLC34A2 gene.
Organic solute transporter alpha, also known as OST-alpha, is a protein which in humans is encoded by the SLC51A gene.
Organic solute transporter beta, also known as OST-beta, is a protein which in humans is encoded by the OSTB gene.
Volixibat is a medication under development as a possible treatment for nonalcoholic steatohepatitis (NASH), the most severe form of non-alcoholic fatty liver disease (NAFLD). No other pharmacotherapy yet exists for NASH, so there is interest in whether volixibat can prove to be both safe and effective. To encourage development and testing, the U.S. Food and Drug Administration (FDA) has issued fast track status.
Members of the Organo Anion Transporter (OAT) Family are membrane transport proteins or 'transporters' that mediate the transport of mainly organic anions across the cell membrane. Therefore, OATPs are present in the lipid bilayer of the cell membrane, acting as the cell's gatekeepers. OATPs belong to the Solute Carrier Family (SLC) and the major facilitator superfamily.
The woolly monkey hepatitis B virus (WMHBV) is a viral species of the Orthohepadnavirus genus of the Hepadnaviridae family. Its natural host is the woolly monkey (Lagothrix), an inhabitant of South America categorized as a New World primate. WMHBV, like other hepatitis viruses, infects the hepatocytes, or liver cells, of its host organism. It can cause hepatitis, liver necrosis, cirrhosis, and hepatocellular carcinoma. Because nearly all species of Lagothrix are threatened or endangered, researching and developing a vaccine and/or treatment for WMHBV is important for the protection of the whole woolly monkey genus.
Bulevirtide, sold under the brand name Hepcludex, is an antiviral medication for the treatment of chronic hepatitis D.
References
- 1 2 3 Anwer MS, Stieger B (2014). "Sodium-dependent bile salt transporters of the SLC10A transporter family: more than solute transporters". Pflügers Arch. 466 (1): 77–89. doi:10.1007/s00424-013-1367-0. PMC 3877701 . PMID 24196564.
- ↑ Hagenbuch B, Stieger B, Foguet M, Labbert H, Meier PJ (December 1991). "Functional expression cloning and characterization of the hepatocyte Na+/bile acid cotransport system". Proc. Natl. Acad. Sci. U.S.A. 88 (23): 10629–33. Bibcode:1991PNAS...8810629H. doi: 10.1073/pnas.88.23.10629 . PMC 52983 . PMID 1961729.
- ↑ Li W, Urban S (2016). "Entry of hepatitis B and hepatitis D virus into hepatocytes: Basic insights and clinical implications". J. Hepatol. 64 (1 Suppl): S32–40. doi:10.1016/j.jhep.2016.02.011. PMC 7114860 . PMID 27084034.
- ↑ Dawson PA (2011). "Role of the intestinal bile acid transporters in bile acid and drug disposition". Drug Transporters. Handbook of Experimental Pharmacology. Vol. 201. pp. 169–203. doi:10.1007/978-3-642-14541-4_4. ISBN 978-3-642-14540-7. PMC 3249407 . PMID 21103970.
- ↑ Acosta A, Camilleri M (2014). "Elobixibat and its potential role in chronic idiopathic constipation". Ther Adv Gastroenterol. 7 (4): 167–75. doi:10.1177/1756283X14528269. PMC 4107709 . PMID 25057297.