| solute carrier family 12 (sodium/potassium/chloride transporters), member 2 |
| Identifiers |
| Symbol |
SLC12A2 |
| Entrez |
6557 |
| HUGO |
10910 |
| OMIM |
600839 |
| RefSeq |
NM_000338 |
| UniProt |
Q13621 |
| Other data |
| Locus |
Chr. 15 q15−q21 |
| solute carrier family 12 (sodium/potassium/chloride transporters), member 1 |
| Identifiers |
| Symbol |
SLC12A1 |
| Entrez |
6558 |
| HUGO |
10911 |
| OMIM |
600840 |
| RefSeq |
NM_001046 |
| UniProt |
P55011 |
| Other data |
| Locus |
Chr. 5 q23.3 |
The Na-K-Cl cotransporter (NKCC) is a protein that aids in the active transport of sodium, potassium, and chloride into and out of cells.[1] There are two varieties of this membrane transport protein, NKCC1 and NKCC2, however these are encoded by two different genes (SLC12A2 and SLC12A1 respectively) and are not isoforms. Two isoforms of the NKCC1/Slc12a2 gene result from keeping (isoform 1) or skipping (isoform 2) exon 21 in the final gene product.[2]
NKCC1 is widely distributed throughout the body; it has important functions in organs that secrete fluids. NKCC2 is found specifically in the kidney, where it serves to extract sodium, potassium, and chloride from the urine so that they can be reabsorbed into the blood.
Contents
- 1 Function
- 2 Genetics
- 3 Kinetics
- 4 See also
- 5 References
- 6 External links
Function
NKCC proteins are membrane transport proteins that transport sodium (Na), potassium (K), and chloride (Cl) ions across the cell membrane. Because they move each solute in the same direction, NKCC proteins are considered symporters. They maintain electroneutrality by moving two positively charged solutes (sodium and potassium) alongside two parts of a negatively charged solute (chloride). Thus the stoichiometry of the NKCC proteins is 1Na:1K:2Cl.
NKCC1
NKCC1 is widely distributed throughout the body, especially in organs that secrete fluids, called exocrine glands.[3] In cells of these organs, NKCC1 is commonly found in the basolateral membrane,[4] the part of the cell membrane closest to the blood vessels. Its basolateral location gives NKCC1 the ability to transport sodium, potassium, and chloride from the blood into the cell. Other transporters assist in the movement of these solutes out of the cell through its apical surface. The end result is that solutes from the blood, particularly chloride, are secreted into the lumen of these exocrine glands, increasing the luminal concentration of solutes and causing water to be secreted by osmosis.
In addition to exocrine glands, NKCC1 is necessary for establishing the potassium-rich endolymph that bathes part of the cochlea, an organ necessary for hearing. Inhibition of NKCC1, as with furosemide or other loop diuretics, can result in deafness.[4]
NKCC1 is also expressed in many regions of the brain during early development, but not in adulthood.[5] This change in NKCC1 presence seems to be responsible for altering responses to the neurotransmitters GABA and glycine from excitatory to inhibitory, which was suggested to be important for early neuronal development. As long as NKCC1 transporters are predominantely active, internal chloride concentrations in neurons is raised in comparison with mature chloride concentrations, which is important for GABA and glycine responses, as respective ligand-gated anion channels are permeable to chloride. With higher internal chloride concentrations, outward driving force for this ions increases, and thus channel opening leads to chloride leaving the cell, thereby depolarizing it. Put another way, increasing internal chloride concentration increases the reversal potential for chloride, given by the Nernst equation. Later in development expression of NKCC1 is reduced, while expression of a KCC2 K-Cl cotransporter increased, thus bringing internal chloride concentration in neurons down to adult values.[6]
NKCC2
NKCC2 is specifically found in cells of the thick ascending limb of the loop of Henle in nephrons, the basic functional units of the kidney. Within these cells, NKCC2 resides in the apical membrane[7] abutting the nephron's lumen, the hollow space containing urine.
Urine in the thick ascending limb of the loop of Henle has a relatively high concentration of sodium. That is, the electrochemical gradient of sodium favors movement of sodium from the urine and into cells. At this region of the nephron, NKCC2 is the major transport protein by which sodium is reabsorbed from the urine and into cells. According to the stoichiometry outlined above, each molecule of sodium reabsorbed brings one molecule of potassium and two molecules of chloride. Sodium goes on to be reabsorbed into the blood, where it contributes to the maintenance of blood pressure.
Furosemide and other loop diuretics inhibit the activity of NKCC2, thereby impairing sodium reabsorption in the thick ascending limb of the loop of Henle. Impaired sodium reabsorption prevents the thick ascending limb from contributing to maintenance of blood pressure. Loop diuretics therefore ultimately result in decreased blood pressure.
The hormone, Vasopressin, stimulates the activity of NKCC2. Vasopressin stimulates sodium chloride reabsorption in the thick ascending limb of the nephron activating signaling pathways. It increases the traffic of the NKCC2 to the membrane and phosphorylate at some serine and threonine sites the cytoplasmic N-terminal of the NKCC2 located in the membrane, increasing its activity; further aiding in water reabsorption in the collecting duct through Aquaporin 2 channels by the creation of a hypo-osmotic filtrate.[8][9]
Genetics
NKCC1 and NKCC2 are encoded by genes on the long arms of chromosomes 15[10] and 5,[11] respectively. A loss of function mutation of NKCC2 produces Bartter syndrome, an autosomal recessive disorder characterized by hypokalemic metabolic alkalosis with normal to low blood pressure.[11]
Kinetics
The energy required to move solutes across the cell membrane is provided by the electrochemical gradient of sodium. Sodium's electrochemical gradient is established by the Na-K ATPase, which is an ATP-dependent enzyme. Since NKCC proteins use sodium's gradient, their activity is indirectly dependent on ATP; for this reason, NKCC proteins are said to move solutes by way of secondary active transport.
See also
- Cotransport
- Cotransporter
References
- ^ Haas M (October 1994). "The Na-K-Cl cotransporters". Am. J. Physiol. 267 (4 Pt 1): C869–85. PMID 7943281.
- ^ Hebert, SC; Mount, DB; Gamba, G (Feb 2004). "Molecular physiology of cation-coupled Cl− cotransport: the SLC12 family.". Pflugers Archiv : European journal of physiology 447 (5): 580–593. doi:10.1007/s00424-003-1066-3. PMID 12739168.
- ^ Haas M, Forbush B (2000). "The Na-K-Cl cotransporter of secretory epithelia". Annu. Rev. Physiol. 62: 515–34. doi:10.1146/annurev.physiol.62.1.515. PMID 10845101.
- ^ a b Delpire E, Lu J, England R, Dull C, Thorne T (June 1999). "Deafness and imbalance associated with inactivation of the secretory Na-K-2Cl co-transporter". Nat. Genet. 22 (2): 192–5. doi:10.1038/9713. PMID 10369265.
- ^ Dzhala VI, Talos DM, Sdrulla DA, Brumback AC, Mathews GC, Benke TA, Delpire E, Jensen FE, Staley KJ (November 2005). "NKCC1 transporter facilitates seizures in the developing brain". Nat. Med. 11 (11): 1205–13. doi:10.1038/nm1301. PMID 16227993.
- ^ Ben-Ari Y, Gaiarsa JL, Tyzio R, Khazipov R (October 2007). "GABA: a pioneer transmitter that excites immature neurons and generates primitive oscillations". Physiol. Rev. 87 (4): 1215–84. doi:10.1152/physrev.00017.2006. PMID 17928584.
- ^ Lytle C, Xu JC, Biemesderfer D, Forbush B (December 1995). "Distribution and diversity of Na-K-Cl cotransport proteins: a study with monoclonal antibodies". Am. J. Physiol. 269 (6 Pt 1): C1496–505. PMID 8572179.
- ^ Rieg T1, Tang T, Uchida S, Hammond HK, Fenton RA, Vallon V. (November 2012). "Adenylyl cyclase 6 enhances NKCC2 expression and mediates vasopressin-induced phosphorylation of NKCC2 and NCC". Am J Pathol 182 (1): 96–106. doi:10.1016/j.ajpath.2012.09.014. PMID 23123217.
- ^ Ares GR, Caceres PS, Ortiz PA. (September 2011). "Molecular regulation of NKCC2 in the thick ascending limb". Am J Physiol Renal Physiol 301 (6): F1143–59. doi:10.1152/ajprenal.00396.2011. PMID 21900458.
- ^ Payne JA, Xu JC, Haas M, Lytle CY, Ward D, Forbush B (July 1995). "Primary structure, functional expression, and chromosomal localization of the bumetanide-sensitive Na-K-Cl cotransporter in human colon". J. Biol. Chem. 270 (30): 17977–85. doi:10.1074/jbc.270.30.17977. PMID 7629105.
- ^ a b Simon DB, Karet FE, Hamdan JM, DiPietro A, Sanjad SA, Lifton RP (June 1996). "Bartter's syndrome, hypokalaemic alkalosis with hypercalciuria, is caused by mutations in the Na-K-2Cl cotransporter NKCC2". Nat. Genet. 13 (2): 183–8. doi:10.1038/ng0696-183. PMID 8640224.
External links
- Sodium-Potassium-Chloride Symporters at the US National Library of Medicine Medical Subject Headings (MeSH)
|
Membrane transport protein: ion pumps, ATPases / ATP synthase (TC 3A2-3A3)
|
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| F-, V-, and A-type ATPase (3.A.2) |
|
H+ (F-type)
|
- H+ transporting, mitochondrial: ATP5A1
- ATP5B
- ATP5C1
- ATP5C2
- ATP5D
- ATP5E
- ATP5F1
- ATP5G1
- ATP5G2
- ATP5G3
- ATP5H
- ATP5I
- ATP5J
- ATP5J2
- ATP5L
- ATP5L2
- ATP5O
- ATP5S
|
|
|
H+ (V-type)
|
- H+ transporting, lysosomal: ATP6AP1
- ATP6AP2
- ATP6V1A
- ATP6V1B1
- ATP6V1B2
- ATP6V1C1
- ATP6V1C2
- ATP6V1D
- ATP6V1E1
- ATP6V1E2
- ATP6V1F
- ATP6V1G1
- ATP6V1G2
- ATP6V1G3
- ATP6V1H
- ATP6V0A1
- ATP6V0A2
- ATP6V0A4
- ATP6V0B
- ATP6V0C
- ATP6V0D1
- ATP6V0D2
- ATP6V0E
- ATP6V0E1
|
|
|
A-ATPase
|
found in Archea
|
|
|
| P-type ATPase (3.A.3) |
- 3.A.3.1.1: Na+/K+ transporting: ATP1A1
- ATP1A2
- ATP1A3
- ATP1A4
- ATP1B1
- ATP1B2
- ATP1B3
- ATP1B4
- ATP1G1
- 3.A.3.1.2: H+/K+
- H+/K+ exchanging: ATP4A
- ATP4B
- 3.A.3.1.4: H+/K+ transporting, nongastric: ATP12A
- 3.A.3.2: Ca+ (SERCA, PMCA, SPCA) / Ca++ transporting: ATP2A1
- ATP2A2
- ATP2A3
- ATP2B1
- ATP2B2
- ATP2B3
- ATP2B4
- ATP2C1
- 3.A.3.5: Cu++ transporting: ATP7A
- ATP7B
- 3.A.3.8.8: flippase: ATP8A2
- Mg++ transporting: ATP3
- Class I, type 8: ATP8A1
- ATP8B1
- ATP8B2
- ATP8B3
- ATP8B4
- Class II, type 9: ATP9A
- ATP9B
- Class V, type 10: ATP10A
- ATP10B
- ATP10D
- Class VI, type 11: ATP11A
- ATP11B
- ATP11C
- type 13: ATP13A1
- ATP13A2
- ATP13A3
- ATP13A4
- ATP13A5
|
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see also ATPase disorders
|
Index of cells
|
|
| Description |
- Structure
- Organelles
- peroxisome
- cytoskeleton
- centrosome
- epithelia
- cilia
- mitochondria
- Membranes
- Membrane transport
- ion channels
- vesicular transport
- solute carrier
- ABC transporters
- ATPase
- oxidoreduction-driven
|
|
| Disease |
- Structural
- peroxisome
- cytoskeleton
- cilia
- mitochondria
- nucleus
- scleroprotein
- Membrane
- channelopathy
- solute carrier
- ATPase
- ABC transporters
- other
- extracellular ligands
- cell surface receptors
- intracellular signalling
- Vesicular transport
- Pore-forming toxins
|
|
|
|
Membrane proteins, carrier proteins: membrane transport proteins solute carrier (TC 2A)
|
|
|
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|
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Ion pumps
|
|
| Symporter, Cotransporter |
- Na+/K+,l-
- Na/Pi3
- Na+/Cl-
- Na/glucose
- Na+/I-
- Cl-/K+
|
|
| Antiporter (exchanger) |
- Na+/H+
- Na+/Ca2+
- Na+/(Ca2+-K+) - Cl-/HCO3- (Band 3)
- Cl-formate exchanger
- Cl-oxalate exchanger
|
|
|
|
|
see also solute carrier disorders
|
Index of cells
|
|
| Description |
- Structure
- Organelles
- peroxisome
- cytoskeleton
- centrosome
- epithelia
- cilia
- mitochondria
- Membranes
- Membrane transport
- ion channels
- vesicular transport
- solute carrier
- ABC transporters
- ATPase
- oxidoreduction-driven
|
|
| Disease |
- Structural
- peroxisome
- cytoskeleton
- cilia
- mitochondria
- nucleus
- scleroprotein
- Membrane
- channelopathy
- solute carrier
- ATPase
- ABC transporters
- other
- extracellular ligands
- cell surface receptors
- intracellular signalling
- Vesicular transport
- Pore-forming toxins
|
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