text: An antiporter (also called exchanger or counter-transporter) is an integral membrane protein involved in secondary active transport. It is a type of cotransporter, which means that uses the movement of one In the case of an antiporter, two or more different molecules or ions are moved across a phospholipid membrane, such as the plasma membrane, in opposite directions, one into the cell and one out of the cell. This is in contrast to symporters, which are another type of cotransporter that moves two or more ions in the same direction.
  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 mechanism is used by both types of cotransporters. It is different from primary active transport, where ATP directly fuels the movement of solutes against their concentration gradients. Because this movement requires energy, primary active transport is utilized by ATP-powered pumps to move ions and small molecules.
  Transport may involve one or more of each type of solute. For example, the Na/Ca exchanger, found in the plasma membrane of many cells, moves three sodium ions in one direction, and one calcium ion in the other. As with sodium in this example, antiporters rely on an established gradient that makes entry of one ion energetically favorable to force the unfavorable movement of a second molecule in the opposite direction. Through their diverse functions, antiporters are involved in various important physiological processes, such as the regulation the strength of cardiac muscle contraction, transport of carbon dioxide by erythrocytes, regulation of cytosolic pH, and accumulation of sucrose in plant vacuoles.