Contribution of Aquaporins to Cellular Water Transport Observed by a Microfluidic Cell Volume Sensor (original) (raw)
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Cellular and Molecular Biology of the Aquaporin Water Channels
Annual Review of Biochemistry, 1999
The high water permeability characteristic of mammalian red cell membranes is now known to be caused by the protein AQP1. This channel freely permits movement of water across the cell membrane, but it is not permeated by other small, uncharged molecules or charged solutes. AQP1 is a tetramer with each subunit containing an aqueous pore likened to an hourglass formed by obversely arranged tandem repeats. Cryoelectron microscopy of reconstituted AQP1 membrane crystals has revealed the three-dimensional structure at 3-6 Å. AQP1 is distributed in apical and basolateral membranes of renal proximal tubules and descending thin limbs as well as capillary endothelia. Ten mammalian aquaporins have been identified in water-permeable tissues and fall into two groupings. Orthodox aquaporins are waterselective and include AQP2, a vasopressin-regulated water channel in renal collecting duct, in addition to AQP0, AQP4, and AQP5. Multifunctional aquaglyceroporins AQP3, AQP7, and AQP9 are permeated by water, glycerol, and some other solutes. Aquaporins are being defined in numerous other species including amphibia, insects, plants, and microbials. Members of the aquaporin family are implicated in numerous physiological processes as well as the pathophysiology of a wide range of clinical disorders.
Beyond water homeostasis: Diverse functional roles of mammalian aquaporins
Biochimica et biophysica acta, 2015
Aquaporin (AQP) water channels are best known as passive transporters of water that are vital for water homeostasis. AQP knockout studies in whole animals and cultured cells, along with naturally occurring human mutations suggest that the transport of neutral solutes through AQPs has important physiological roles. Emerging biophysical evidence suggests that AQPs may also facilitate gas (CO2) and cation transport. AQPs may be involved in cell signalling for volume regulation and controlling the subcellular localization of other proteins by forming macromolecular complexes. This review examines the evidence for these diverse functions of AQPs as well their physiological relevance. As well as being crucial for water homeostasis, AQPs are involved in physiologically important transport of molecules other than water, regulation of surface expression of other membrane proteins, cell adhesion, and signalling in cell volume regulation. Elucidating the full range of functional roles of AQPs ...
Rapid Aquaporin Translocation Regulates Cellular Water Flow
Journal of Biological Chemistry, 2012
Background: Aquaporin channels ensure appropriate membrane permeability to water in all cells. Results: Following a hypotonic stimulus, subcellular localization of aquaporin 1 occurs via a mechanism dependent on transient receptor potential channels, extracellular calcium influx, calmodulin, and the phosphorylation of two threonines (157 and 239) of aquaporin 1. Conclusion: Rapid translocation of aquaporin 1 regulates membrane water permeability. Significance: This mechanism may serve as a prototype for the rapid regulation of aquaporin function.
American Journal of Biomedical Sciences, 2018
Aquaporins (AQPs) form pores in the membranes of cells and selectively conduct water molecules through the membrane, while preventing the passage of ions such as sodium and potassium and other small molecules. The water movement through AQPs is considered to be facilitated simply dependent on the osmotic gradient. There are subtypes of AQPs; classical aquaporins or orthodox AQPs (AQP0, AQP1, AQP2, AQP4, AQP5) permeable only to water molecules ; aquaglyceroporins (AQP3, 7, 9 and 10) permeable to uncharged solutes, such as glycerol, CO2, ammonia and urea in addition to water and unorthodox AQPs, (AQP6, AQP8, AQP11 and AQP12) with unknown functions. The specific distribution of AQP in certain cell types of an organ often reflects a precise function. AQP0 is present in the eye lens for maintaining its transparency. AQP1 is widely distributed water channel in the body. It is mostly expressed in kidneys, lungs, red blood cells, liver, skin, intervertebral disc peripheral and central nervous system. It is involved in angiogenesis, cell migration, cell growth and countercurrent concentration. Its defect shows a protective action against edema in the lungs. AQP2 is expressed in kidney collecting duct and inner ear for water transport in presence of vasopressin; its mutations in kidney can cause nephrogenic diabetes insipidus and its mutation in inner ear provokes Menieres disease. AQP3 is the most abundant skin aquaglyceroporin, where AQP3 facilitated water and glycerol transport plays an important role in hydration of mammalian skin epidermis and proliferation and differentiation of keratinocytes. It is also found in kidney collecting duct, conjunctiva of the eye, oesophagus, colon, spleen, stomach, small intestine, intervertebral disc and respiratory tract airway epithelium. AQP4 is found in astroglial cells at blood-brain barrier and spinal cord, kidney collecting duct, glandular epithelia, airways, skeletal muscle, stomach and retina. AQP4 null mice showed altered cerebral water balance with protection from brain edema. AQP5 helps glandular water secretion so, it expressed in glandular epithelia, corneal epithelium, alveolar epithelium and gastrointestinal tract. AQP6 is expressed in kidney collecting duct intercalated cells, retina, parotid gland acinar cells, inner ear, and brain synaptic vesicles. It is involved in chloride, urea and nitrate permeability. AQP6 may functionally interact with H+-ATPase in the vesicles to regulate intra-vesicle pH and acid-base balance.
Molecular Aspects of Medicine, 2012
After a decade of work on the water permeability of red blood cells (RBC) Benga group in Cluj-Napoca, Romania, discovered in 1985 the first water channel protein in the RBC membrane. The discovery was reported in publications in 1986 and reviewed in subsequent years. The same protein was purified by chance by Agre group in Baltimore, USA, in 1988, who called in 1991 the protein CHIP28 (CHannel forming Integral membrane Protein of 28 kDa), suggesting that it may play a role in linkage of the membrane skeleton to the lipid bilayer. In 1992 the Agre group identified CHIP28's water transport property. One year later CHIP28 was named aquaporin 1, abbreviated as AQP1. In this review the molecular structure-function relationships of AQP1 are presented. In the natural or model membranes AQP1 is in the form of a homotetramer, however, each monomer has an independent water channel (pore). The three-dimensional structure of AQP1 is described, with a detailed description of the channel (pore), the molecular mechanisms of permeation through the channel of water molecules and exclusion of protons. The permeability of the pore to gases (CO 2 , NH 3 , NO, O 2) and ions is also mentioned. I have also reviewed the functional roles and medical implications of AQP1 expressed in various organs and cells (microvascular endothelial cells, kidney, central nervous system, eye, lacrimal and salivary glands, respiratory apparatus, gastrointestinal tract, hepatobiliary compartments, female and male reproductive system, inner ear, skin). The role of AQP1 in cell migration and angiogenesis in relation with cancer, the genetics of AQP1 and mutations in human subjects are also mentioned. The role of AQP1 in red blood cells is discussed based on our comparative studies of water permeability in over 30 species.
Aquaporins: A Multidisciplinary Perspective on The Water Channel Proteins
Acta Medica, 2020
Aquaporins are unique water channel proteins located at cell membranes that possess high water permeability and high solute rejection. Their primary function is to maintain the osmotic balance of the cells via regulating the water transport. However, their discovery had also provided the scientists to understand the pathophysiology of some diseases. In fact, aquaporins are shown to be strongly related to cancer by taking part in several tumor-related processes such as cell migration, cell proliferation and cell adhesion. Other than their functions in human body, recently, aquaporins have started to be used in engineering biomimetic membranes, for different applications such as desalination. This review investigates the properties and functions of the aquaporins in a multidisciplinary point of view and demonstrates the recent developments in aquaporin-based research.