The renal outer medullary potassium channel (ROMK) is an ATP-dependent
potassium channel
Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of c ...
(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 440px
Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classica ...
in the
cortical collecting duct
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct system is the last part of nephron and participates in elec ...
(CCD) of the
nephron
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ...
. In humans, ROMK is encoded by the ''KCNJ1'' (potassium inwardly-rectifying channel, subfamily J, member 1)
gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
.
Multiple transcript variants encoding different isoforms have been found for this gene.
Function
Potassium channel
Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of c ...
s 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
ATP may refer to:
Companies and organizations
* Association of Tennis Professionals, men's professional tennis governing body
* American Technical Publishers, employee-owned publishing company
* ', a Danish pension
* Armenia Tree Project, non ...
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).
ROMK was identified as the pore-forming component of the
mitochondrial ATP-sensitive potassium (
mitoKATP) channel, known to play a critical role in
cardioprotection against
ischemic-reperfusion injury in the heart
as well as in the protection against
hypoxia-induced brain injury from
stroke or other
ischemic
Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...
attacks.
Klotho is a
beta-glucuronidase
Beta-glucuronidases are members of the glycosidase family of enzymes that catalyze breakdown of complex carbohydrates. Human β-glucuronidase is a type of glucuronidase (a member of glycosidase Family 2) that catalyzes hydrolysis of β-D-gluc ...
-like enzyme that activates ROMK by removal of
sialic acid Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone.
The term "sialic acid" (from the Greek for saliva, - ''síalon'') was first introduced by Swedish biochemist Gunnar Blix in 1952. The most common member of this ...
.
Clinical significance
Mutations in this gene have been associated with antenatal
Bartter syndrome
Bartter syndrome (BS) is a rare inherited disease characterised by a defect in the thick ascending limb of the loop of Henle, which results in low potassium levels (hypokalemia), increased blood pH ( alkalosis), and normal to low blood pressure. ...
, which is characterized by salt wasting, hypokalemic alkalosis, hypercalciuria, and low blood pressure.
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. Sgk1 kinase has also been reported to phosphorylate ROMK, resulting in an increase of channels on the apical surface of the distal tubule.
Sgk1 is in turn regulated by the mineralocorticoid receptor such an effect may contribute to the kaliuretic action of aldosterone.
References
Further reading
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
External links
*
NDI terminology page
{{Ion channels, g3
Ion channels