Sodium Glucose Linked Transporter (SGLT)

The sodium glucose linked transporters (SGLTs) are responsible for transporting glucose along cell membranes by using the electrical gradient of Na⁺. There are six variants of the SGLT proteins that are encoded on the SLC5 gene. All of these proteins are transmembrane proteins (spans the whole of the phospholipid bilayer) all with 14 alpha helices. The functions of the SGLT1, SGLT2 and SGLT3 are known, however the functions of SGLT4, SGLT5 and SGLT6 are still unknown.

SGLT1

The SGLT1 protein is expressed in the membrane of the intestine and the kidneys. SGLT1 that is located in the proximal renal tubules, absorbs glucose along with two Na⁺ ions.  For this example the Na⁺ concentration gradient is produced by the Na⁺/K⁺ ATPase. When the glucose in in the epithelial cells, it is then transported out of the cell through facilitated diffusion by the GLUT2 protein.

SGLT2

The SGLT2 protein is expressed in the membrane of the kidneys. This protein can also transport galactose but not as rapidly as glucose. This transporter has a lower affinity to glucose in comparison the SGLT1.

SGLT3

This protein is mainly expressed in skeletal muscle and the small intestine. It is believed that this protein is a glucose sensor in mainly cholinergic neurones and skeletal muscle as it is unable to transport glucose regardless of the presence of Na⁺.