Potassium in biology

Potassium is an essential mineral micronutrient and is the main intracellular ion for all types of cells. It is important in maintaining fluid and electrolyte balance in the bodies of humans and animals.[1][2] Potassium is necessary for the function of all living cells, and is thus present in all plant and animal tissues. It is found in especially high concentrations within plant cells, and in a mixed diet, it is most highly concentrated in fruits. The high concentration of potassium in plants, associated with comparatively very low amounts of sodium there, historically resulted in potassium first being isolated from the ashes of plants (potash), which in turn gave the element its modern name. The high concentration of potassium in plants means that heavy crop production rapidly depletes soils of potassium, and agricultural fertilizers consume 93% of the potassium chemical production of the modern world economy.

The functions of potassium and sodium in living organisms are quite different. Animals, in particular, employ sodium and potassium differentially to generate electrical potentials in animal cells, especially in nervous tissue. Potassium depletion in animals, including humans, results in various neurological dysfunctions. Characteristic concentrations of potassium in model organisms are: 30-300mM in E. coli, 300mM in budding yeast, 100mM in mammalian cell and 4mM in blood plasma.[3]

Function in plants

Function in animals

Potassium is the major cation (positive ion) inside animal cells, while sodium is the major cation outside animal cells. The difference between the concentrations of these charged particles causes a difference in electric potential between the inside and outside of cells, known as the membrane potential. The balance between potassium and sodium is maintained by ion transporters in the cell membrane. All potassium ion channels are tetramers with several conserved secondary structural elements. A number of potassium channel structures have been solved including voltage gated,[4][5][6] ligand gated,[7][8][9][10][11] tandem-pore,[12][13][14] and inwardly rectifying channels,[15][16][17][18][19] from prokaryotes and eukaryotes. The cell membrane potential created by potassium and sodium ions allows the cell to generate an action potential—a "spike" of electrical discharge. The ability of cells to produce electrical discharge is critical for body functions such as neurotransmission, muscle contraction, and heart function.[20]

Dietary reference intake

The Food and Nutrition Board of the U.S. Institute of Medicine sets Estimated Average Requirements (EARs), Recommended Dietary Allowances (RDAs), Adequate Intakes (AIs) for when there is not sufficient information to set EARs and RDAs, and Tolerable Upper Intake Levels (ULs). Collectively the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes. The current AI for potassium for women and men ages 14 and up is 4700 mg. AI for pregnancy equals 4700 mg/day. AI for lactation equals 5100 mg/day. For infants 0–6 months 400 mg, 6–12 months 700 mg, 1–3 years 3000 mg, 4–8 years 3800 mg and 9–13 years 4500 mg.[21]

For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For potassium labeling purposes 100% of the Daily Value was 3500 mg, but as of May 2016 it has been revised to 4700 mg. A table of the pre-change adult Daily Values is provided at Reference Daily Intake. Food and supplement companies have until July 2018 to comply with the change.

Deficiency

High blood pressure/Hypertension

Diets low in potassium increase risk of hypertension, stroke and cardiovascular disease.[22][23]

Hypokalemia

A severe shortage of potassium in body fluids may cause a potentially fatal condition known as hypokalemia. Hypokalemia typically results from loss of potassium through diarrhea, diuresis, or vomiting. Symptoms are related to alterations in membrane potential and cellular metabolism. Symptoms include muscle weakness and cramps, paralytic ileus, ECG abnormalities, intestinal paralysis, decreased reflex response and (in severe cases) respiratory paralysis, alkalosis and arrhythmia.

In rare cases, habitual consumption of large amounts of black licorice has resulted in hypokalemia. Licorice contains a compound (Glycyrrhizin) that increases urinary excretion of potassium.[24]

Insufficient intake

Adult women in the United States consume on average half the AI, for men two-thirds. For all adults, fewer than 5% exceed the AI.[25] Similarly, in the European Union, insufficient potassium intake is widespread.[26]

Food sources

Eating a variety of foods that contain potassium is the best way to get an adequate amount. Foods with high sources of potassium include kiwifruit, orange juice, potatoes, bananas, coconut, avocados, apricots, parsnips and turnips, although many other fruits, vegetables, legumes, and meats contain potassium.

Common foods very high in potassium:[27]

The most concentrated foods (per 100 grams) are:[27]

Side effects and toxicity

Gastrointestinal symptoms are the most common side effects of potassium supplements, including nausea, vomiting, abdominal discomfort, and diarrhea. Taking potassium with meals or taking a microencapsulated form of potassium may reduce gastrointestinal side effects.

Hyperkalemia is the most serious adverse reaction to potassium. Hyperkalemia occurs when potassium builds up faster than the kidneys can remove it. It is most common in individuals with renal failure. Symptoms of hyperkalemia may include tingling of the hands and feet, muscular weakness, and temporary paralysis. The most serious complication of hyperkalemia is the development of an abnormal heart rhythm (arrhythmia), which can lead to cardiac arrest.

Although hyperkalemia is rare in healthy individuals, oral doses greater than 18 grams taken at one time in individuals not accustomed to high intakes can lead to hyperkalemia. Supplements sold in the U.S. are supposed to contain no more than 99 mg of potassium per serving.

See also

References

  1. ↑ Pohl, Hanna R.; Wheeler, John S.; Murray, H. Edward (2013). "Chapter 2. Sodium and Potassium in Health and Disease". In Astrid Sigel, Helmut Sigel and Roland K. O. Sigel. Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. 13. Springer. pp. 29–47. doi:10.1007/978-94-007-7500-8_2.
  2. ↑
    • Clausen, Michael Jakob Voldsgaard; Poulsen, Hanne (2013). "Chapter 3 Sodium/Potassium Homeostasis in the Cell". In Banci, Lucia (Ed.). Metallomics and the Cell. Metal Ions in Life Sciences. 12. Springer. ISBN 978-94-007-5560-4. doi:10.1007/978-94-007-5561-1_3. electronic-book ISBN 978-94-007-5561-1 ISSN 1559-0836 electronic-ISSN 1868-0402
  3. ↑ Milo, Ron; Philips, Rob. "Cell Biology by the Numbers: What are the concentrations of different ions in cells?". book.bionumbers.org. Retrieved 23 March 2017.
  4. ↑ Santos JS, Asmar-Rovira GA, Han GW, Liu W, Syeda R, Cherezov V, Baker KA, Stevens RC, Montal M (Dec 2012). "Crystal structure of a voltage-gated K+ channel pore module in a closed state in lipid membranes.". J Biol Chem. 287: 43063–70. PMC 3522301 Freely accessible. PMID 23095758. doi:10.1074/jbc.M112.415091.
  5. ↑ Long SB, Campbell EB, Mackinnon R (August 2005). "Crystal structure of a mammalian voltage-dependent Shaker family K+ channel". Science. 309: 897–903. PMID 16002581. doi:10.1126/science.1116269.
  6. ↑ Jiang Y, Lee A, Chen J, et al. (May 2003). "X-ray structure of a voltage-dependent K+ channel". Nature. 423: 33–41. PMID 12721618. doi:10.1038/nature01580.
  7. ↑ Jiang Y, Lee A, Chen J, Cadene M, Chait BT, MacKinnon R (May 2002). "Crystal structure and mechanism of a calcium-gated potassium channel". Nature. 417: 515–22. PMID 12037559. doi:10.1038/417515a.
  8. ↑ Yuan P, Leonetti MD, Pico AR, Hsiung Y, MacKinnon R (July 2010). "Structure of the human BK channel Ca2+-activation apparatus at 3.0 A resolution". Science. 329: 182–6. PMC 3022345 Freely accessible. PMID 20508092. doi:10.1126/science.1190414.
  9. ↑ Wu Y, Yang Y, Ye S, Jiang Y (July 2010). "Structure of the gating ring from the human large-conductance Ca(2+)-gated K(+) channel". Nature. 466: 393–7. PMC 2910425 Freely accessible. PMID 20574420. doi:10.1038/nature09252.
  10. ↑ Leonetti MD, Yuan P, Hsiung Y, Mackinnon R (Nov 2012). "Functional and structural analysis of the human SLO3 pH- and voltage-gated K+ channel.". Proc Natl Acad Sci U S A. 109: 19274–9. PMC 3511096 Freely accessible. PMID 23129643. doi:10.1073/pnas.1215078109.
  11. ↑ Kong C, Zeng W, Ye S, Chen L, Sauer DB, Lam Y, Derebe MG, Jiang Y (2012). "Distinct gating mechanisms revealed by the structures of a multi-ligand gated K(+) channel.". Elife. 1: e00184. PMC 3510474 Freely accessible. PMID 23240087. doi:10.7554/eLife.00184.
  12. ↑ Brohawn SG, del Mármol J, MacKinnon R (January 2012). "Crystal structure of the human K2P TRAAK, a lipid- and mechano-sensitive K+ ion channel". Science. 335: 436–41. PMC 3329120 Freely accessible. PMID 22282805. doi:10.1126/science.1213808.
  13. ↑ Miller AN, Long SB (January 2012). "Crystal structure of the human two-pore domain potassium channel K2P1". Science. 335: 432–6. PMID 22282804. doi:10.1126/science.1213274.
  14. ↑ Dong YY, Pike AC, Mackenzie A, McClenaghan C, Aryal P, Dong L, Quigley A, Grieben M, Goubin S, Mukhopadhyay S, Ruda GF, Clausen MV, Cao L, Brennan PE, Burgess-Brown NA, Sansom MS, Tucker SJ, Carpenter EP (Mar 2015). "K2P channel gating mechanisms revealed by structures of TREK-2 and a complex with Prozac.". Science. 347: 1256–9. PMID 25766236. doi:10.1126/science.1261512.
  15. ↑ Clarke OB, Caputo AT, Hill AP, Vandenberg JI, Smith BJ, Gulbis JM (Jun 2010). "Domain reorientation and rotation of an intracellular assembly regulate conduction in Kir potassium channels.". Cell. 141: 1018–29. PMID 20564790. doi:10.1016/j.cell.2010.05.003.
  16. ↑ Kuo A, Gulbis JM, Antcliff JF, Rahman T, Lowe ED, Zimmer J, Cuthbertson J, Ashcroft FM, Ezaki T, Doyle DA (Jun 2003). "Crystal structure of the potassium channel KirBac1.1 in the closed state.". Science. 300: 1922–6. PMID 12738871. doi:10.1126/science.1085028.
  17. ↑ Whorton MR, MacKinnon R (Sep 2011). "Crystal structure of the mammalian GIRK2 K+ channel and gating regulation by G proteins, PIP2, and sodium.". Cell. 147: 199–208. PMC 3243363 Freely accessible. PMID 21962516. doi:10.1016/j.cell.2011.07.046.
  18. ↑ Nishida M, MacKinnon R (Dec 2002). "Structural basis of inward rectification: cytoplasmic pore of the G protein-gated inward rectifier GIRK1 at 1.8 A resolution.". Cell. 111: 957–65. PMID 12507423. doi:10.1016/S0092-8674(02)01227-8.
  19. ↑ Tao X, Avalos JL, Chen J, MacKinnon R (Dec 2009). "Crystal structure of the eukaryotic strong inward-rectifier K+ channel Kir2.2 at 3.1 A resolution.". Science. 326: 1668–74. PMC 2819303 Freely accessible. PMID 20019282. doi:10.1126/science.1180310.
  20. ↑ Mikko Hellgren; Lars Sandberg; Olle Edholm (2006). "A comparison between two prokaryotic potassium channels (KirBac1.1 and KcsA) in a molecular dynamics (MD) simulation study". Biophys. Chem. 120 (1): 1–9. PMID 16253415. doi:10.1016/j.bpc.2005.10.002.
  21. ↑ Potassium. IN: Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academy Press. 2005, PP.186-268.
  22. ↑ Aburto NJ, Hanson S, Gutierrez H, Hooper L, Elliott P, Cappuccio FP (2013). "Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses". BMJ. 346: f1378. PMC 4816263 Freely accessible. PMID 23558164. doi:10.1136/bmj.f1378.
  23. ↑ D'Elia L, Barba G, Cappuccio FP, Strazzullo P (2011). "Potassium intake, stroke, and cardiovascular disease a meta-analysis of prospective studies". J. Am. Coll. Cardiol. 57 (10): 1210–9. PMID 21371638. doi:10.1016/j.jacc.2010.09.070.
  24. ↑ Mumoli N, Cei M (2008). "Licorice-induced hypokalemia". Int. J. Cardiol. 124 (3): e42–4. PMID 17320224. doi:10.1016/j.ijcard.2006.11.190.
  25. ↑ What We Eat In America, NHANES 2013-2014.
  26. ↑ http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowPDF&ProduktNr=223977&Ausgabe=230671&ArtikelNr=83312&filename=83312.pdf Energy and Nutrient Intake in the European Union
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