ROMK explained

The renal outer medullary potassium channel (ROMK) is an ATP-dependent potassium channel (K_ir1.1) that transports potassium out of cells. It plays an important role in potassium recycling in the thick ascending limb (TAL) and potassium secretion in the cortical collecting duct (CCD) of the nephron. In humans, ROMK is encoded by the KCNJ1 (potassium inwardly-rectifying channel, subfamily J, member 1) gene.^{[1] [2] [3]} Multiple transcript variants encoding different isoforms have been found for this gene.

Function

Potassium channels are present in most mammalian cells, where they participate in a wide range of physiologic responses. The protein encoded by this gene is an integral membrane protein and inward-rectifier type potassium channel. It is inhibited by internal ATP and probably plays an important role in potassium homeostasis. The encoded protein has a greater tendency to allow potassium to flow into a cell rather than out of a cell, which has (hence the term "inwardly rectifying" referring to corresponding currents in electrophysiology, but has limited physiological relevance).^[4] ROMK was identified as the pore-forming component of the mitochondrial ATP-sensitive potassium (mitoK_ATP) channel, known to play a critical role in cardioprotection against ischemic-reperfusion injury in the heart^[5] as well as in the protection against hypoxia-induced brain injury from stroke or other ischemic attacks.

Klotho is a beta-glucuronidase-like enzyme that activates ROMK by removal of sialic acid.^{[6] [7]}

Clinical significance

Mutations in this gene have been associated with antenatal Bartter syndrome, which is characterized by salt wasting, hypokalemic alkalosis, hypercalciuria, and low blood pressure.^[4]

Role in hypokalemia and magnesium deficiency

The ROMK channels are inhibited by magnesium in the nephron's normal physiologic state. In states of hypokalemia (a state of potassium deficiency), concurrent magnesium deficiency results in a state of hypokalemia that may be more difficult to correct with potassium replacement alone. This may be directly due to decreased inhibition of the outward potassium current in states where magnesium is low. Conversely, magnesium deficiency alone is not likely to cause a state of hypokalemia.^[8] Sgk1 kinase has also been reported to phosphorylate ROMK, resulting in an increase of channels on the apical surface of the distal tubule.^[9] Sgk1 is in turn regulated by the mineralocorticoid receptor such an effect may contribute to the kaliuretic action of aldosterone.

Further reading

• O'Connell AD, Leng Q, Dong K, MacGregor GG, Giebisch G, Hebert SC . Phosphorylation-regulated endoplasmic reticulum retention signal in the renal outer-medullary K+ channel (ROMK) . Proceedings of the National Academy of Sciences of the United States of America . 102 . 28 . 9954–9 . July 2005 . 15987778 . 1175014 . 10.1073/pnas.0504332102 . 2005PNAS..102.9954O . free .
• Kubo Y, Adelman JP, Clapham DE, Jan LY, Karschin A, Kurachi Y, Lazdunski M, Nichols CG, Seino S, Vandenberg CA . International Union of Pharmacology. LIV. Nomenclature and molecular relationships of inwardly rectifying potassium channels . Pharmacological Reviews . 57 . 4 . 509–26 . December 2005 . 16382105 . 10.1124/pr.57.4.11 . 11588492 .
• Brochard K, Boyer O, Blanchard A, Loirat C, Niaudet P, Macher MA, Deschenes G, Bensman A, Decramer S, Cochat P, Morin D, Broux F, Caillez M, Guyot C, Novo R, Jeunemaître X, Vargas-Poussou R . Phenotype-genotype correlation in antenatal and neonatal variants of Bartter syndrome . Nephrology, Dialysis, Transplantation . 24 . 5 . 1455–64 . May 2009 . 19096086 . 10.1093/ndt/gfn689 . free .
• Lee JR, Shieh RC . Structural changes in the cytoplasmic pore of the Kir1.1 channel during pHi-gating probed by FRET . Journal of Biomedical Science . 16 . 1 . 29 . March 2009 . 19272129 . 2672938 . 10.1186/1423-0127-16-29 . free .
• Nüsing RM, Pantalone F, Gröne HJ, Seyberth HW, Wegmann M . Expression of the potassium channel ROMK in adult and fetal human kidney . Histochemistry and Cell Biology . 123 . 6 . 553–9 . June 2005 . 15895241 . 10.1007/s00418-004-0742-5 . 24421285 .
• Cho JT, Guay-Woodford LM . Heterozygous mutations of the gene for Kir 1.1 (ROMK) in antenatal Bartter syndrome presenting with transient hyperkalemia, evolving to a benign course . Journal of Korean Medical Science . 18 . 1 . 65–8 . February 2003 . 12589089 . 3055000 . 10.3346/jkms.2003.18.1.65 .
• Ji W, Foo JN, O'Roak BJ, Zhao H, Larson MG, Simon DB, Newton-Cheh C, State MW, Levy D, Lifton RP . Rare independent mutations in renal salt handling genes contribute to blood pressure variation . Nature Genetics . 40 . 5 . 592–599 . May 2008 . 18391953 . 3766631 . 10.1038/ng.118 .
• Nozu K, Fu XJ, Kaito H, Kanda K, Yokoyama N, Przybyslaw Krol R, Nakajima T, Kajiyama M, Iijima K, Matsuo M . A novel mutation in KCNJ1 in a Bartter syndrome case diagnosed as pseudohypoaldosteronism . Pediatric Nephrology . 22 . 8 . 1219–23 . August 2007 . 17401586 . 10.1007/s00467-007-0468-4 . 36736809 .
• Lin D, Kamsteeg EJ, Zhang Y, Jin Y, Sterling H, Yue P, Roos M, Duffield A, Spencer J, Caplan M, Wang WH . Expression of tetraspan protein CD63 activates protein-tyrosine kinase (PTK) and enhances the PTK-induced inhibition of ROMK channels . The Journal of Biological Chemistry . 283 . 12 . 7674–81 . March 2008 . 18211905 . 10.1074/jbc.M705574200 . free . 2066/70313 . free .
• Wang HR, Liu Z, Huang CL . Domains of WNK1 kinase in the regulation of ROMK1 . American Journal of Physiology. Renal Physiology . 295 . 2 . F438–45 . August 2008 . 18550644 . 2519181 . 10.1152/ajprenal.90287.2008 .
• Yoo D, Kim BY, Campo C, Nance L, King A, Maouyo D, Welling PA . Cell surface expression of the ROMK (Kir 1.1) channel is regulated by the aldosterone-induced kinase, SGK-1, and protein kinase A . The Journal of Biological Chemistry . 278 . 25 . 23066–75 . June 2003 . 12684516 . 10.1074/jbc.M212301200 . free .
• Cha SK, Hu MC, Kurosu H, Kuro-o M, Moe O, Huang CL . Regulation of renal outer medullary potassium channel and renal K(+) excretion by Klotho . Molecular Pharmacology . 76 . 1 . 38–46 . July 2009 . 19349416 . 2701452 . 10.1124/mol.109.055780 .
• Nanazashvili M, Li H, Palmer LG, Walters DE, Sackin H . Moving the pH gate of the Kir1.1 inward rectifier channel . Channels . 1 . 1 . 21–8 . 2007 . 19170254 . 10.4161/chan.3707 . free .
• Liu Z, Wang HR, Huang CL . Regulation of ROMK channel and K+ homeostasis by kidney-specific WNK1 kinase . The Journal of Biological Chemistry . 284 . 18 . 12198–206 . May 2009 . 19244242 . 2673288 . 10.1074/jbc.M806551200 . free .
• Yoo D, Flagg TP, Olsen O, Raghuram V, Foskett JK, Welling PA . Assembly and trafficking of a multiprotein ROMK (Kir 1.1) channel complex by PDZ interactions . The Journal of Biological Chemistry . 279 . 8 . 6863–73 . February 2004 . 14604981 . 10.1074/jbc.M311599200 . free .
• Tobin MD, Tomaszewski M, Braund PS, Hajat C, Raleigh SM, Palmer TM, Caulfield M, Burton PR, Samani NJ . Common variants in genes underlying monogenic hypertension and hypotension and blood pressure in the general population . Hypertension . 51 . 6 . 1658–64 . June 2008 . 18443236 . 10.1161/HYPERTENSIONAHA.108.112664 . free . 2381/4837 . free .
• He G, Wang HR, Huang SK, Huang CL . Intersectin links WNK kinases to endocytosis of ROMK1 . The Journal of Clinical Investigation . 117 . 4 . 1078–87 . April 2007 . 17380208 . 1821066 . 10.1172/JCI30087 .
• Murthy M, Cope G, O'Shaughnessy KM . The acidic motif of WNK4 is crucial for its interaction with the K channel ROMK . Biochemical and Biophysical Research Communications . 375 . 4 . 651–4 . October 2008 . 18755144 . 10.1016/j.bbrc.2008.08.076 .
• Lazrak A, Liu Z, Huang CL . Antagonistic regulation of ROMK by long and kidney-specific WNK1 isoforms . Proceedings of the National Academy of Sciences of the United States of America . 103 . 5 . 1615–20 . January 2006 . 16428287 . 1360592 . 10.1073/pnas.0510609103 . 2006PNAS..103.1615L . free .
• Welling PA, Ho K . A comprehensive guide to the ROMK potassium channel: form and function in health and disease . American Journal of Physiology. Renal Physiology . 297 . 4 . F849–63 . October 2009 . 19458126 . 10.1152/ajprenal.00181.2009 . 2775575.

External links

• • NDI terminology page

Notes and References

1. Ho K, Nichols CG, Lederer WJ, Lytton J, Vassilev PM, Kanazirska MV, Hebert SC . Cloning and expression of an inwardly rectifying ATP-regulated potassium channel . Nature . 362 . 6415 . 31–8 . March 1993 . 7680431 . 10.1038/362031a0 . 1993Natur.362...31H . 4332298 .
2. Yano H, Philipson LH, Kugler JL, Tokuyama Y, Davis EM, Le Beau MM, Nelson DJ, Bell GI, Takeda J . Alternative splicing of human inwardly rectifying K+ channel ROMK1 mRNA . Molecular Pharmacology . 45 . 5 . 854–60 . May 1994 . 8190102 .
3. Kubo Y, Adelman JP, Clapham DE, Jan LY, Karschin A, Kurachi Y, Lazdunski M, Nichols CG, Seino S, Vandenberg CA . International Union of Pharmacology. LIV. Nomenclature and molecular relationships of inwardly rectifying potassium channels . Pharmacological Reviews . 57 . 4 . 509–26 . December 2005 . 16382105 . 10.1124/pr.57.4.11 . 11588492 .
4. Web site: Entrez Gene: potassium inwardly-rectifying channel.
5. Foster DB, Ho AS, Rucker J, Garlid AO, Chen L, Sidor A, Garlid KD, O'Rourke B . Mitochondrial ROMK channel is a molecular component of mitoK(ATP) . Circulation Research . 111 . 4 . 446–54 . August 2012 . 22811560 . 3560389 . 10.1161/circresaha.112.266445 .
6. Cha SK, Ortega B, Kurosu H, Rosenblatt KP, Kuro-O M, Huang CL . Removal of sialic acid involving Klotho causes cell-surface retention of TRPV5 channel via binding to galectin-1 . . 105 . 28 . 9805–9810 . 2008 . 10.1073/pnas.0803223105 . 2474477 . 18606998 . 2008PNAS..105.9805C . free .
7. Huang CL . Regulation of ion channels by secreted Klotho: mechanisms and implications . . 77 . 10 . 855–860 . 2010 . 10.1038/ki.2010.73 . 20375979 . free .
8. Huang CL, Kuo E . Mechanism of hypokalemia in magnesium deficiency . Journal of the American Society of Nephrology . 18 . 10 . 2649–2652 . October 2007 . 17804670 . 10.1681/asn.2007070792 . free .
9. Yoo D, Kim BY, Campo C, Nance L, King A, Maouyo D, Welling PA . Cell surface expression of the ROMK (Kir 1.1) channel is regulated by the aldosterone-induced kinase, SGK-1, and protein kinase A . The Journal of Biological Chemistry . 278 . 25 . 23066–23075 . June 2003 . 12684516 . 10.1074/jbc.M212301200 . free .