Aquaporin 2
Encyclopedia
AQP2 is found in the apical cell membranes of the kidney
's collecting duct principal cells and in intracellular
vesicles
located throughout the cell.
.
The basic job of aquaporin 2 is to reabsorb water from the urine while its being removed from the blood by the kidney. aquaporin 2 is in kidney epithelial cells and usually lies dormant in intracellular vesicle membranes, but when it is needed vasopressin binds to the cell surface vasopressin receptor, activating a signaling pathway that causes the aquaporin 2 containing vesicles to fuse with the plasma membrane so the aquaporin 2 can be used by the cell.
This aquaporin
is regulated in two ways by the peptide hormone
vasopressin
:
This aquaporin
is also regulated by food intake. Fasting reduces expression of this aquaporin independently of vasopressin.
, which can autosomal dominant or recessive. Mutations in the vasopressin receptor cause a similar X-linked phenotype.
Lithium
, which is often used to treat bipolar disorder
, can cause acquired diabetes insipidus
(characterized by the excretion of large volumes of dilute urine) by decreasing the expression of the AQP2 gene.
The expression of the AQP2 gene is increased during conditions associated with water retention such as pregnancy
and congestive heart failure
.
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
's collecting duct principal cells and in intracellular
Intracellular
Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...
vesicles
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
located throughout the cell.
Regulation
It is the only aquaporin regulated by vasopressinVasopressin
Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
.
The basic job of aquaporin 2 is to reabsorb water from the urine while its being removed from the blood by the kidney. aquaporin 2 is in kidney epithelial cells and usually lies dormant in intracellular vesicle membranes, but when it is needed vasopressin binds to the cell surface vasopressin receptor, activating a signaling pathway that causes the aquaporin 2 containing vesicles to fuse with the plasma membrane so the aquaporin 2 can be used by the cell.
This aquaporin
Aquaporin
Aquaporins are proteins embedded in the cell membrane that regulate the flow of water.Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells....
is regulated in two ways by the peptide hormone
Peptide hormone
Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.Like other proteins, peptide hormones are synthesized in cells from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the...
vasopressin
Vasopressin
Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
:
- short-term regulation (minutes) through trafficking of AQP2 vesicles to the apical region where they fuse with the apical plasma membrane
- long-term regulation (days) through an increase in AQP2 gene expression.
This aquaporin
Aquaporin
Aquaporins are proteins embedded in the cell membrane that regulate the flow of water.Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells....
is also regulated by food intake. Fasting reduces expression of this aquaporin independently of vasopressin.
Clinical significance
Mutations in this channel are associated with nephrogenic diabetes insipidusNephrogenic diabetes insipidus
Nephrogenic diabetes insipidus is a form of diabetes insipidus due primarily to pathology of the kidney. This is in contrast to central/neurogenic diabetes insipidus, which is caused by insufficient levels of antidiuretic hormone /Argenine Vasopressin...
, which can autosomal dominant or recessive. Mutations in the vasopressin receptor cause a similar X-linked phenotype.
Lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
, which is often used to treat bipolar disorder
Bipolar disorder
Bipolar disorder or bipolar affective disorder, historically known as manic–depressive disorder, is a psychiatric diagnosis that describes a category of mood disorders defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or...
, can cause acquired diabetes insipidus
Diabetes insipidus
Diabetes insipidus is a condition characterized by excessive thirst and excretion of large amounts of severely diluted urine, with reduction of fluid intake having no effect on the concentration of the urine. There are several different types of DI, each with a different cause...
(characterized by the excretion of large volumes of dilute urine) by decreasing the expression of the AQP2 gene.
The expression of the AQP2 gene is increased during conditions associated with water retention such as pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
and congestive heart failure
Congestive heart failure
Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...
.