Limits...
Aquaporins: The renal water channels.

Agarwal SK, Gupta A - Indian J Nephrol (2008)

Bottom Line: Nephrotic syndrome is characterized by excessive sodium and water reabsorption, although in spite of this, patients do not develop hyponatremia.There are some conditions in which aquaporin expression has been found to increase such as experimentally induced heart failure, cirrhosis, and pregnancy.Further insights into the molecular structure and biology of aquaporins will help to lay a foundation for the development of future drugs.

View Article: PubMed Central - PubMed

Affiliation: Department of Nephrology, All India Institute of Medical Sciences, New Delhi - 110 029, India.

ABSTRACT
Water is the most abundant molecule in any cell. Specialized membrane channel, proteins called aquaporins, facilitate water transport across cell membranes. At least seven aquaporins (AQP): 1, 2, 3, 4, 6, 7, and 11 are expressed in the kidneys. Aquaporins play a role in both the short-term and long-term regulation of water balance as well as in the pathophysiology of water balance disorders. Aquaporin is composed of a single peptide chain consisting of approximately 270 amino acids. Inherited central and nephrogenic diabetes insipidus are primarily due to the decreased expression of AQP2 while mutation in the AQP2 molecule is responsible for inherited central diabetes insipidus. In acquired causes of nephrogenic diabetes insipidus, there is a downregulation of AQP2 expression in the inner medulla of the kidney. Nephrotic syndrome is characterized by excessive sodium and water reabsorption, although in spite of this, patients do not develop hyponatremia. There is a marked downregulation of both AQP2 and AQP3 expression, which could be a physiologic response to extracellular water reabsorption in patients with nephrotic syndrome. There are some conditions in which aquaporin expression has been found to increase such as experimentally induced heart failure, cirrhosis, and pregnancy. Some drugs such as cisplatin and cyclosporine, also alter the expression of aquaporins. The three-pore model of peritoneal transport depicts the importance of aquaporins. Thus, the understanding of renal water channels has solved the mystery behind many water balance disorders. Further insights into the molecular structure and biology of aquaporins will help to lay a foundation for the development of future drugs.

No MeSH data available.


Related in: MedlinePlus

Structure of aquaporin 1
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2813137&req=5

Figure 0001: Structure of aquaporin 1

Mentions: Aquaporin is composed of a single peptide chain consisting of approximately 270 amino acids. The deduced amino acid sequence of AQP1 predicted six membrane-spanning domains with intracellular amino (N) and carboxy (C) termini. There are three extracellular loops (A, C, and E) and two intracellular loops (B and D). Highly conserved regions are present within loops B and E, each of which contains the consensus motif, asparagine-proline-alanine (NPA). When these two loops are folded into the lipid bilayer and surrounded by transmembrane domains, they may form a hydrophilic path for the water transfer through the lipid bilayer. This model is called the “hourglass model” [Fig. 1].3 Fourier transform infrared spectroscopy was used to further characterize the secondary structure of AQP1 and the results revealed that six closely associated alpha helices span the lipid membrane.4 Moreover, the 3D structure of AQP1 was determined at 6Å resolution by cryoelectron microscopy. Each AQP1 monomer has six-tilted, bilayer-spanning alpha helices, which form a right-handed bundle surrounding a central density. These studies also confirmed the organization of a tetrameric complex in the membrane.5


Aquaporins: The renal water channels.

Agarwal SK, Gupta A - Indian J Nephrol (2008)

Structure of aquaporin 1
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2813137&req=5

Figure 0001: Structure of aquaporin 1
Mentions: Aquaporin is composed of a single peptide chain consisting of approximately 270 amino acids. The deduced amino acid sequence of AQP1 predicted six membrane-spanning domains with intracellular amino (N) and carboxy (C) termini. There are three extracellular loops (A, C, and E) and two intracellular loops (B and D). Highly conserved regions are present within loops B and E, each of which contains the consensus motif, asparagine-proline-alanine (NPA). When these two loops are folded into the lipid bilayer and surrounded by transmembrane domains, they may form a hydrophilic path for the water transfer through the lipid bilayer. This model is called the “hourglass model” [Fig. 1].3 Fourier transform infrared spectroscopy was used to further characterize the secondary structure of AQP1 and the results revealed that six closely associated alpha helices span the lipid membrane.4 Moreover, the 3D structure of AQP1 was determined at 6Å resolution by cryoelectron microscopy. Each AQP1 monomer has six-tilted, bilayer-spanning alpha helices, which form a right-handed bundle surrounding a central density. These studies also confirmed the organization of a tetrameric complex in the membrane.5

Bottom Line: Nephrotic syndrome is characterized by excessive sodium and water reabsorption, although in spite of this, patients do not develop hyponatremia.There are some conditions in which aquaporin expression has been found to increase such as experimentally induced heart failure, cirrhosis, and pregnancy.Further insights into the molecular structure and biology of aquaporins will help to lay a foundation for the development of future drugs.

View Article: PubMed Central - PubMed

Affiliation: Department of Nephrology, All India Institute of Medical Sciences, New Delhi - 110 029, India.

ABSTRACT
Water is the most abundant molecule in any cell. Specialized membrane channel, proteins called aquaporins, facilitate water transport across cell membranes. At least seven aquaporins (AQP): 1, 2, 3, 4, 6, 7, and 11 are expressed in the kidneys. Aquaporins play a role in both the short-term and long-term regulation of water balance as well as in the pathophysiology of water balance disorders. Aquaporin is composed of a single peptide chain consisting of approximately 270 amino acids. Inherited central and nephrogenic diabetes insipidus are primarily due to the decreased expression of AQP2 while mutation in the AQP2 molecule is responsible for inherited central diabetes insipidus. In acquired causes of nephrogenic diabetes insipidus, there is a downregulation of AQP2 expression in the inner medulla of the kidney. Nephrotic syndrome is characterized by excessive sodium and water reabsorption, although in spite of this, patients do not develop hyponatremia. There is a marked downregulation of both AQP2 and AQP3 expression, which could be a physiologic response to extracellular water reabsorption in patients with nephrotic syndrome. There are some conditions in which aquaporin expression has been found to increase such as experimentally induced heart failure, cirrhosis, and pregnancy. Some drugs such as cisplatin and cyclosporine, also alter the expression of aquaporins. The three-pore model of peritoneal transport depicts the importance of aquaporins. Thus, the understanding of renal water channels has solved the mystery behind many water balance disorders. Further insights into the molecular structure and biology of aquaporins will help to lay a foundation for the development of future drugs.

No MeSH data available.


Related in: MedlinePlus