other ion will move from the cytoplasmic space into the exoplasmic space. An example of an antiporter is the sodium-calcium exchanger. The sodium-calcium exchanger functions to remove excess calcium from the cytoplasmic space into the exoplasmic space against its concentration gradient by coupling its transport with the transport of sodium from the exoplasmic space down its concentration gradient (established by the active transport of sodium out of the cell by the sodium-potassium pump) into the cytoplasmic space. The sodium-calcium exchanger exchanges 3 sodium ions for 1 calcium ion and represents a cation antiporter. Cells also contain anion antiporters such as the Band 3 (or AE1) anion transport protein. This cotransporter is an important integral protein in mammalian erythrocytes and moves chloride ion and bicarbonate ion in a one-to-one ratio across the plasma membrane based only on the concentration gradient of the two ions. The AE1 antiporter is essential in the removal of carbon dioxide waste that is converted to bicarbonate inside the erythrocyte. Symporters In contrast to antiporters, symporters move ions or molecules in the same direction. In this case both ions being transported will be moved either from the exoplasmic space into the cytoplasmic space or from the cytoplasmic space into the exoplasmic space. An example of a symporter is the sodium-glucose linked transporter or SGLT. The SGLT functions to couple the transport of sodium in the exoplasmic space down its concentration gradient (again, established by the active transport of sodium out of the cell by the sodium-potassium pump) into the cytoplasmic space to the transport of glucose in the exoplasmic space against its concentration gradient into the cytoplasmic space. The SGLT couples the movement of 1 glucose ion with the movement of 2 sodium ions. Examples of cotransporters Na+/glucose cotransporter (SGLT1) – is also known as sodium-glucose cotransporter 1 and is encoded by the SLC5A1 gene. SGLT1 is an electrogenic transporter as the sodium electrochemical gradient drives glucose uphill into the cells. SGLT1 is a high affinity Na+ /glucose cotransporter that has an important role in transferring sugar across the epithelial cells of renal proximal tubules and of the intestine, in particular the small intestine. Na+/phosphate cotransporter (NaPi) – Sodium-phosphate cotransporters are from the SLC34 and SLC20 protein families. They are also found across the epithelial cells of renal proximal tubule and of the small intestine. It transfers inorganic phosphate into cells through active transport with the help