An organic anion-transporting polypeptide (OATP) is a membrane transport protein that mediates the transport of organic anions across the cell membrane

Cell membrane

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

. Organic anion-transporting proteins belong to the solute carrier family

Solute carrier family

The solute carrier group of membrane transport proteins include over 300 members organized into 51 families. The SLC gene nomenclature system was originally proposed by the Human Genome Organization and is the basis for the official HUGO names of the genes that encode these transporters...

, more specific, subfamily 21 (organic anion transporting).

Function

Organic anion transporters may carry bile acid

Bile acid

Bile acids are steroid acids found predominantly in the bile of mammals. Bile salts are bile acids compounded with a cation, usually sodium. In humans, the salts of taurocholic acid and glycocholic acid represent approximately eighty percent of all bile salts. The two major bile acids are cholic...

s as well as bilirubin

Bilirubin

Bilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...

 over the basolateral membrane (facing sinusoids) in hepatocytes, as well as other anions for excretion in bile.

They also transport the dye bromsulphthalein

Bromsulphthalein

Bromsulphthalein is a dye used in liver function tests. Its excretion is measured....

, availing it as a liver-testing substance.

Other OAT proteins transport organic anions across the basolateral side of renal proximal tubule cells during renal secretion.

Proteins

These organic anion transporting proteins have been found in human cells.

Abbreviation	Protein Name	Location
SLCO1A2 SLCO1A2 Solute carrier organic anion transporter family member 1A2 is a protein that in humans is encoded by the SLCO1A2 gene.-Further reading:...	Solute carrier organic anion transporter family member 1A2	Liver
SLCO1B1 SLCO1B1 Solute carrier organic anion transporter family member 1B1 is a protein that in humans is encoded by the SLCO1B1 gene.-Further reading:...	Solute carrier organic anion transporter family member 1B1	Liver
SLCO1B3 SLCO1B3 Solute carrier organic anion transporter family member 1B3 also known as organic anion-transporting polypeptide 1B3 is a protein that in humans is encoded by the SLCO1B3 gene....	Solute carrier organic anion transporter family member 1B3	Liver
SLCO1B4
SLCO1C1
SLCO2A1
SLCO2B1 SLCO2B1 Solute carrier organic anion transporter family member 2B1 is a protein that in humans is encoded by the SLCO2B1 gene.-Further reading:...	Solute carrier organic anion transporter family member 2B1	Many
SLCO3A1 SLCO3A1 Solute carrier organic anion transporter family member 3A1 is a protein that in humans is encoded by the SLCO3A1 gene.-Further reading:...	Solute carrier organic anion transporter family member 3A1
SLCO4A1 SLCO4A1 Solute carrier organic anion transporter family member 4A1 is a protein that in humans is encoded by the SLCO4A1 gene.-Further reading:...	Solute carrier organic anion transporter family member 4A1
SLCO4C1 OATP4C1 Organic anion transporter polypeptide 4C1 or OATP4C1 is a human protein. It is also known as "solute carrier organic anion transporter family member 4A1". OATP4C1 is coded for by the gene SLCO4C1, which is located on chromosome 5q21...		Kidneys
SLCO5A1
SLCO6A1

Organic anion transporter (OAT) family

The SLC22A gene family codes for organic anion transporter (OAT) proteins. The OAT family plays the central role in renal organic anion

Organic anion

Organic anions are chemically heterogeneous substances possessing a carbon backbone and a net negative charge. Organic anions are conjugate bases of organic acids. The following table lists some of the organic anions and their conjugate acids which are substrates of the organic acid transporter ...

 transport. OAT1, OAT3, OAT4, and URAT1 are expressed in the proximal tubular cells of the kidneys. OAT1 and OAT3 mediate uptake of a wide range of relatively small and hydrophilic organic anion

Organic anion

Organic anions are chemically heterogeneous substances possessing a carbon backbone and a net negative charge. Organic anions are conjugate bases of organic acids. The following table lists some of the organic anions and their conjugate acids which are substrates of the organic acid transporter ...

s from plasma

Blood plasma

Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

. URAT1 transports those organic anions from the cytoplasm

Cytoplasm

The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

 of the proximal tubular cells into the lumen of the nephron

Nephron

The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron....

. Organic anion transporters are within the organic cation transport proteins

Organic cation transport proteins

An organic cation transport protein mediates the transport of organic cations across the cell membrane. These proteins are members of the solute carrier family, subfamily 22. This family of proteins can also transport zwitterions and anions, though it is a different subfamily of solute carrier...

 family.

Abbreviation	Gene	Protein Name	Location
OAT1 Organic anion transporter 1 The organic anion transporter 1 also known as solute carrier family 22 member 6 is a protein that in humans is encoded by the SLC22A6 gene. It is a member of the organic anion transporter family of proteins...	SLC22A6	Solute carrier family 22 member 6	Brain, placenta, eyes, smooth muscle, and the basolateral membrane of renal proximal tubule cells
OAT2	SLC22A7 SLC22A7 Solute carrier family 22 member 7 is a protein that in humans is encoded by the SLC22A7 gene.-Further reading:...	Solute carrier family 22 member 7	Liver, and kidneys
OAT3	SLC22A8 SLC22A8 Solute carrier family 22 member 8 is a protein that in humans is encoded by the SLC22A8 gene.-Further reading:...	Solute carrier family 22 member 8	Bone, brain, eyes, liver, adrenal glands, and the basolateral membrane of renal proximal tubule cells
OAT4	SLC22A11 SLC22A11 Solute carrier family 22 member 11 is a protein that in humans is encoded by the SLC22A11 gene.-Further reading:...	Solute carrier family 22 member 11	Placenta, and the apical membrane of the renal proximal tubule cells
OAT5	SLC22A10 SLC22A10 Solute carrier family 22 member 10 , also known as organic anion transporter 5 , is a protein that in humans is encoded by the SLC22A10 gene....	Solute carrier family 22 member 10	Kidneys
URAT1	SLC22A12 SLC22A12 Solute carrier family 22 , member 12, also known as SLC22A12 and URAT1, is a protein which in humans is encoded by the SLC22A12 gene.-Function:...	Solute carrier family 22 member 12	Brain, vascular smooth muscle cells, and the apical membrane of the renal proximal tubule cells