Antiporter

An antiporter (also called exchanger or counter-transporter) is an integral membrane protein involved in secondary active transport of two or more different molecules or ions (i.e., solutes) across a phospholipid membrane such as the plasma membrane in opposite directions.

In secondary active transport, one species of solute moves along its electrochemical gradient, allowing a different species to move against its own electrochemical gradient. This movement is in contrast to primary active transport, in which all solutes are moved against their concentration gradients, fueled by ATP.

Transport may involve one or more of each type of solute. For example, the Na+/Ca2+ exchanger, used by many cells to remove cytoplasmic calcium, exchanges one calcium ion for three sodium ions.