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Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane, controlling the flow of ions across secretory and epithelial cells, and regulating cell volume. Ion channels are present in the membranes of all cells. Ion channels are one of the two classes of ionophoric proteins, the other being ion transporters.
Israel Hanukoglu is a Turkish-born Israeli scientist. He is a full professor of biochemistry and molecular biology at Ariel University and former science and technology adviser to the prime minister of Israel (1996–1999). He is founder of Israel Science and Technology Directory.
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 cell functions.
Amiloride, sold under the trade name Midamor among others, is a medication typically used with other medications to treat high blood pressure or swelling due to heart failure or cirrhosis of the liver. Amiloride is classified as a potassium-sparing diuretic. Amiloride is often used together with another diuretic, such as a thiazide or loop diuretic. It is taken by mouth. Onset of action is about two hours and it lasts for about a day.
Cyclic nucleotide–gated ion channels or CNG channels are ion channels that function in response to the binding of cyclic nucleotides. CNG channels are nonselective cation channels that are found in the membranes of various tissue and cell types, and are significant in sensory transduction as well as cellular development. Their function can be the result of a combination of the binding of cyclic nucleotides and either a depolarization or a hyperpolarization event. Initially discovered in the cells that make up the retina of the eye, CNG channels have been found in many different cell types across both the animal and the plant kingdoms. CNG channels have a very complex structure with various subunits and domains that play a critical role in their function. CNG channels are significant in the function of various sensory pathways including vision and olfaction, as well as in other key cellular functions such as hormone release and chemotaxis. CNG channels have also been found to exist in prokaryotes, including many spirochaeta, though their precise role in bacterial physiology remains unknown.
Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels.
The epithelial sodium channel(ENaC), (also known as amiloride-sensitive sodium channel) is a membrane-bound ion channel that is selectively permeable to sodium ions (Na+). It is assembled as a heterotrimer composed of three homologous subunits α or δ, β, and γ, These subunits are encoded by four genes: SCNN1A, SCNN1B, SCNN1G, and SCNN1D. The ENaC is involved primarily in the reabsorption of sodium ions at the collecting ducts of the kidney's nephrons. In addition to being implicated in diseases where fluid balance across epithelial membranes is perturbed, including pulmonary edema, cystic fibrosis, COPD and COVID-19, proteolyzed forms of ENaC function as the human salt taste receptor.
The SCNN1B gene encodes for the β subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by SCNN1A, SCNN1G, and SCNN1D.
The SCNN1A gene encodes for the α subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by SCNN1B, SCNN1G, and SCNN1D.
The SCNN1G gene encodes for the γ subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by SCNN1A, SCNN1B, and SCNN1D.
Acid-sensing ion channel 1 (ASIC1) also known as amiloride-sensitive cation channel 2, neuronal (ACCN2) or brain sodium channel 2 (BNaC2) is a protein that in humans is encoded by the ASIC1 gene. The ASIC1 gene is one of the five paralogous genes that encode proteins that form trimeric acid-sensing ion channels (ASICs) in mammals. The cDNA of this gene was first cloned in 1996. The ASIC genes have splicing variants that encode different proteins that are called isoforms.
Sodium channel subunit beta-3 is a protein that in humans is encoded by the SCN3B gene. Two alternatively spliced variants, encoding the same protein, have been identified.
Acid-sensing ion channel 3 (ASIC3) also known as amiloride-sensitive cation channel 3 (ACCN3) or testis sodium channel 1 (TNaC1) is a protein that in humans is encoded by the ASIC3 gene. The ASIC3 gene is one of the five paralogous genes that encode proteins that form trimeric acid-sensing ion channels (ASICs) in mammals. The cDNA of this gene was first cloned in 1998. The ASIC genes have splicing variants that encode different proteins that are called isoforms.
Acid-sensing ion channel 2 (ASIC2) also known as amiloride-sensitive cation channel 1, neuronal (ACCN1) or brain sodium channel 1 (BNaC1) is a protein that in humans is encoded by the ASIC2 gene. The ASIC2 gene is one of the five paralogous genes that encode proteins that form trimeric acid-sensing ion channels (ASICs) in mammals. The cDNA of this gene was first cloned in 1996. The ASIC genes have splicing variants that encode different proteins that are called isoforms.
The SCNN1D gene encodes for the δ (delta) subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by SCNN1A, SCNN1B, and SCNN1G.
Mechanosensitive channels (MSCs), mechanosensitive ion channels or stretch-gated ion channels are membrane proteins capable of responding to mechanical stress over a wide dynamic range of external mechanical stimuli. They are present in the membranes of organisms from the three domains of life: bacteria, archaea, and eukarya. They are the sensors for a number of systems including the senses of touch, hearing and balance, as well as participating in cardiovascular regulation and osmotic homeostasis (e.g. thirst). The channels vary in selectivity for the permeating ions from nonselective between anions and cations in bacteria, to cation selective allowing passage Ca2+, K+ and Na+ in eukaryotes, and highly selective K+ channels in bacteria and eukaryotes.
Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive sodium channels activated by extracellular protons permeable to Na+. ASIC1 also shows low Ca2+ permeability. ASIC proteins are a subfamily of the ENaC/Deg superfamily of ion channels. These genes have splice variants that encode for several isoforms that are marked by a suffix. In mammals, acid-sensing ion channels (ASIC) are encoded by five genes that produce ASIC protein subunits: ASIC1, ASIC2, ASIC3, ASIC4, and ASIC5. Three of these protein subunits assemble to form the ASIC, which can combine into both homotrimeric and heterotrimeric channels typically found in both the central nervous system and peripheral nervous system. However, the most common ASICs are ASIC1a and ASIC1a/2a and ASIC3. ASIC2b is non-functional on its own but modulates channel activity when participating in heteromultimers and ASIC4 has no known function. On a broad scale, ASICs are potential drug targets due to their involvement in pathological states such as retinal damage, seizures, and ischemic brain injury.
Acid-sensing ion channel 4 (ASIC4) also known as amiloride-sensitive cation channel 4 (ACCN4) is a protein that in humans is encoded by the ASIC4 gene. The ASIC4 gene is one of the five paralogous genes that encode proteins that form trimeric acid-sensing ion channels (ASICs) in mammals. The cDNA of this gene was first cloned in 2000. The ASIC genes have splicing variants that encode different proteins that are called isoforms.
KcsA (Kchannel of streptomyces A) is a prokaryotic potassium channel from the soil bacterium Streptomyces lividans that has been studied extensively in ion channel research. The pH activated protein possesses two transmembrane segments and a highly selective pore region, responsible for the gating and shuttling of K+ ions out of the cell. The amino acid sequence found in the selectivity filter of KcsA is highly conserved among both prokaryotic and eukaryotic K+ voltage channels; as a result, research on KcsA has provided important structural and mechanistic insight on the molecular basis for K+ ion selection and conduction. As one of the most studied ion channels to this day, KcsA is a template for research on K+ channel function and its elucidated structure underlies computational modeling of channel dynamics for both prokaryotic and eukaryotic species.
Voltage-gated sodium channels (VGSCs), also known as voltage-dependent sodium channels (VDSCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (e.g., muscle, glial cells, neurons, etc.) with a permeability to the sodium ion Na+. They are the main channels involved in action potential of excitable cells.
References
- 1 2 Hanukoglu I (2017). "ASIC and ENaC type sodium channels: Conformational states and the structures of the ion selectivity filters". FEBS Journal. 284 (4): 525–545. doi:10.1111/febs.13840. PMID 27580245. S2CID 24402104.
- ↑ Schaefer, L; Sakai, H; Mattei, M; Lazdunski, M; Lingueglia, E (14 April 2000). "Molecular cloning, functional expression and chromosomal localization of an amiloride-sensitive Na(+) channel from human small intestine". FEBS Letters. 471 (2–3): 205–10. Bibcode:2000FEBSL.471..205S. doi: 10.1016/s0014-5793(00)01403-4 . PMID 10767424.
- ↑ Babinski K, Catarsi S, Biagini G, Séguéla P (Sep 2000). "Mammalian ASIC2a and ASIC3 subunits co-assemble into heteromeric proton-gated channels sensitive to Gd3+". The Journal of Biological Chemistry. 275 (37): 28519–25. doi: 10.1074/jbc.M004114200 . hdl: 11380/304669 . PMID 10842183.
- ↑ Hanukoglu I, Hanukoglu A (Jan 2016). "Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases". Gene. 579 (2): 95–132. doi:10.1016/j.gene.2015.12.061. PMC 4756657 . PMID 26772908.
