Chloride shift

Chloride shift

Chloride shift (also known as the Hamburger shift or Hamburger's phenomenon, named after Hartog Jakob Hamburger (1859–1924), Dutch physiologist) 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 because the equilibrium shifts to replace CO2, and consequently bicarbonate in the red blood cells will move out into the serum. To balance the charges when bicarbonate exits the cell, a chloride anion from the plasma enters the red blood cell. 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.

Key feature to remember here is that,carbonic anhydrase enzyme is found inside the red blood cells and not in the plasma. So carbon dioxide that diffuses into the blood from tissue, further diffuses into red blood cell, gets converted to bicarbonate. This bicarbonate moves down its concentration gradient into the plasma. To maintain electroneutrality anion chloride moves from plasma into the red blood cell.

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. PMC 370872. PMID 6793631. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=370872. 
  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 (25 June 1980). "Oxygen-linked binding sites for inorganic anions to hemoglobin". J. Biol. Chem. 255 (12): 5525–9. PMID 7380825. http://www.jbc.org/cgi/reprint/255/12/5525. 



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