<P> An antiporter (also called exchanger or counter-transporter) is a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions . Na / H antiporters have been reviewed . </P> <P> 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 . </P> <P> Transport may involve one or more of each type of solute . For example, the Na / Ca exchanger, used by many cells to remove cytoplasmic calcium, exchanges one calcium ion for three sodium ions . </P>

The sodium-proton exchanger is an example of a