Cotransportere

Cotransportere, a term used in some languages for cotransporters, refers to membrane proteins that mediate secondary active transport by coupling the movement of one or more solutes to the electrochemical gradient of another ion, typically sodium or hydrogen. They differ from channels, which provide a pore for ions, and from primary active transporters that directly use ATP to move substrates.

Cotransportere are divided into two main types: symporters, which transport substrates in the same direction across the membrane, and antiporters (exchangers), which move substrates in opposite directions. The energy for transport comes from the gradient of the coupling ion, which is maintained by primary pumps such as Na+/K+-ATPase.

Representative examples include the sodium-glucose cotransporters SGLT1 and SGLT2, which reabsorb glucose in the intestine and kidney, and the NKCC family (NKCC1 and NKCC2), which cotransport sodium, potassium, and chloride in various tissues and in the kidney. Numerous other sodium- or proton-coupled transporters move amino acids, nucleotides, or ions in a similar fashion.

Mechanistically, the transporter binds its substrates on one side of the membrane, undergoes conformational changes, and releases them on the opposite side, with the ion gradient driving the process rather than direct ATP hydrolysis. Regulation occurs through trafficking to the plasma membrane, phosphorylation, and hormonal signals. Pharmacological inhibitors targeting cotransportere include SGLT2 inhibitors for type 2 diabetes and loop diuretics that affect NKCC function. Genetic defects can lead to tubulopathies and other disorders affecting fluid and electrolyte balance.