Antiporter

An antiporter (also called exchanger or counter-transporter) is an integral membrane protein that uses secondary active transport to move two or more molecules in opposite directions across a phospholipid membrane. It is a type of cotransporter, which means that uses the energetically favorable movement of one molecule down its electrochemical gradient to power the energetically unfavorable movement of another molecule up its electrochemical gradient. This is in contrast to symporters, which are another type of cotransporter that moves two or more ions in the same direction, and primary active transport, which is directly powered by ATP.^[2]

Illustration of an antiporter and the concentration gradients of its transport substances^[3]

Transport may involve one or more of each type of solute. For example, the Na⁺/Ca²⁺ 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.^[4] 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.^[2]

^ Connectivid-D (2021-09-04). "Membrane proteins involved in active transport can function as uniporters". Retrieved 2024-04-10. One molecule one direction, symporters: two molecules one direction or antiporters: two molecules opposite directions.
^ ^a ^b Lodish HF (2021). Molecular cell biology (Ninth ed.). Austin: Macmillan Learning. ISBN 978-1-319-20852-3.
^ Dittmar E (2017-11-12). "This picture represents antiport". Retrieved 2024-04-10. The yellow triangle shows the concentration gradient for the yellow circles while the blue triangle shows the concentration gradient for the blue circles and the purple rods are the transport protein bundle. The blue circles are moving against their concentration gradient through a transport protein which requires energy while the yellow circles move down their concentration gradient which releases energy. The yellow circles produce more energy through chemiosmosis than what is required to move the blue circles so the movement is coupled and some energy is cancelled out. One example is the sodium-proton exchanger which allows protons to go down their concentration gradient into the cell while pumping sodium out of the cell.
^ Yu SP, Choi DW (June 1997). "Na(+)-Ca2+ exchange currents in cortical neurons: concomitant forward and reverse operation and effect of glutamate". The European Journal of Neuroscience. 9 (6): 1273–1281. doi:10.1111/j.1460-9568.1997.tb01482.x. PMID 9215711.

[1] Connectivid-D (2021-09-04). "Membrane proteins involved in active transport can function as uniporters". Retrieved 2024-04-10. One molecule one direction, symporters: two molecules one direction or antiporters: two molecules opposite directions.

[Lodish_2021-2] Lodish HF (2021). Molecular cell biology (Ninth ed.). Austin: Macmillan Learning. ISBN 978-1-319-20852-3.

[3] Dittmar E (2017-11-12). "This picture represents antiport". Retrieved 2024-04-10. The yellow triangle shows the concentration gradient for the yellow circles while the blue triangle shows the concentration gradient for the blue circles and the purple rods are the transport protein bundle. The blue circles are moving against their concentration gradient through a transport protein which requires energy while the yellow circles move down their concentration gradient which releases energy. The yellow circles produce more energy through chemiosmosis than what is required to move the blue circles so the movement is coupled and some energy is cancelled out. One example is the sodium-proton exchanger which allows protons to go down their concentration gradient into the cell while pumping sodium out of the cell.

[Yu_1997-4] Yu SP, Choi DW (June 1997). "Na(+)-Ca2+ exchange currents in cortical neurons: concomitant forward and reverse operation and effect of glutamate". The European Journal of Neuroscience. 9 (6): 1273–1281. doi:10.1111/j.1460-9568.1997.tb01482.x. PMID 9215711.

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