Kotransportører

Kotransportører, also known as cotransporters or symporters, are a type of membrane transport protein found in the cell membranes of both prokaryotic and eukaryotic organisms. They function by facilitating the movement of two different solute molecules across a biological membrane simultaneously. Crucially, both solutes move in the same direction, either into or out of the cell. This coupled transport mechanism relies on the electrochemical gradient of one of the transported solutes, typically an ion like sodium (Na+) or potassium (K+), to drive the movement of the other solute against its own concentration gradient.

The energy for cotransport is derived from the stored potential energy in the ion gradient. This gradient is usually maintained by the cell's ion pumps, such as the sodium-potassium pump. When the ion moves down its electrochemical gradient, it releases energy that is then used by the cotransporter to move the second solute. This process is therefore a form of secondary active transport, as it indirectly utilizes energy, unlike primary active transport which directly uses ATP.

Examples of cotransporters include the sodium-glucose cotransporter (SGLT) family, which are vital for glucose reabsorption in the kidneys and absorption in the intestines. Another significant group are the sodium-calcium exchangers (NCX), important for regulating intracellular calcium levels in cells like neurons and cardiomyocytes. The specific ions and molecules transported, as well as their physiological roles, vary widely depending on the cell type and the organism.