Claudin-2 is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the CLDN2 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

. It belongs to the group of claudin

Claudin

Claudins are a family of proteins that are the most important components of the tight junctions, where they establish the paracellular barrier that controls the flow of molecules in the intercellular space between the cells of an epithelium...

s.

Function

Claudin-2 is expressed in cation-leaky epithelia

Epithelium

Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...

 such as that of the kidney

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...

 proximal tubule. Mice that are deficient

Knockout mouse

A knockout mouse is a genetically engineered mouse in which researchers have inactivated, or "knocked out," an existing gene by replacing it or disrupting it with an artificial piece of DNA...

 in claudin-2 have reduced reabsorption

Reabsorption

In physiology, reabsorption or tubular reabsorption is the flow of glomerular filtrate from the proximal tubule of the nephron into the peritubular capillaries, or from the urine into the blood...

 of Na⁺ in the proximal tubule, consistent with a role in paracellular transport

Paracellular transport

Paracellular transport refers to the transfer of substances between cells of an epithelium.It is in contrast to "transcellular transport", where the substances travel through the cell, passing through both the apical membrane and basolateral membrane....

. Similar results have been obtained with cultured cells.

Further reading