A type of secondary active transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na+ or H+) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.
In cotransport, the direction of transport is the same for both the driving ion and driven ion/molecule (into the cell or out of the cell).
An example is the Na+/glucose cotransporter (SGLT), which couples the movement of Na+ into the cell down its electrochemical gradient to the movement of glucose into the cell against its concentration gradient.
Cotransport is also commonly referred to as symport.
Transport proteins that are involved in this type of transport are referred to as cotransporters or symporters.