Chloride shift

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Chloride shift is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO3-) and chloride (Cl-) across the membrane of red blood cells.[1] Carbon dioxide (CO2) generated in tissues enters the blood and dissolves in water in the red blood cells to form carbonic acid (H2CO3), which then dissociates to form bicarbonate (HCO-3) and a hydrogen ion (H+). When carbon dioxide levels fall as the blood passes through the lungs, bicarbonate levels fall in the serum and bicarbonate moves out of the red blood cells. To balance the charges when bicarbonate exits the cell, a chloride anion from the plasma enters the red blood cell when the bicarbonate anion leaves. Reverse changes occur in the lungs when carbon dioxide is eliminated from the blood. Here, the exchange of bicarbonate for chloride in red blood cells flushes the bicarbonate from the blood and increases the rate of gas exchange.[2] This chloride shift may also regulate the affinity of hemoglobin for oxygen through the chloride ion acting as an allosteric effector.[3]

Reaction (as it occurs in the lung)

   PLASMA                RBC

   HCO3- --> --> -->    HCO3-
 
   Na+                   K+

   Cl- <-- <-- <-- <--   Cl-

Bicarbonate in the red blood cell (RBC) exchanging with chloride from plasma


[edit] References

  1. ^ Crandall ED, Mathew SJ, Fleischer RS, Winter HI, Bidani A (1981). "Effects of inhibition of RBC HCO3-/Cl- exchange on CO2 excretion and downstream pH disequilibrium in isolated rat lungs". J. Clin. Invest. 68 (4): 853–62. doi:10.1172/JCI110340. PMID 6793631. 
  2. ^ Westen EA, Prange HD (2003). "A reexamination of the mechanisms underlying the arteriovenous chloride shift". Physiol. Biochem. Zool. 76 (5): 603–14. doi:10.1086/380208. PMID 14671708. 
  3. ^ Nigen AM, Manning JM, Alben JO (1980). "Oxygen-linked binding sites for inorganic anions to hemoglobin". J. Biol. Chem. 255 (12): 5525–9. PMID 7380825. 


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