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Aquaporin‐1 and HCO 3 − ‐Cl − transporter‐mediated transport of CO 2 across the human erythrocyte membrane
Author(s) -
Blank Michael E.,
Ehmke Heimo
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.040113
Subject(s) - chemistry , dids , membrane transport , transporter , intracellular , biophysics , membrane , intracellular ph , facilitated diffusion , carbonic anhydrase , bicarbonate , red blood cell , aquaporin , membrane potential , aquaporin 1 , cell membrane , biochemistry , biology , enzyme , mechanical engineering , organic chemistry , inlet , water channel , engineering , gene
Recent studies have suggested that aquaporin‐1 (AQP1) as well as the HCO 3 − ‐Cl − transporter may be involved in CO 2 transport across biological membranes, but the physiological importance of this route of gas transport remained unknown. We studied CO 2 transport in human red blood cell ghosts at physiological temperatures (37 °C). Replacement of inert with CO 2 ‐containing gas above a stirred cell suspension caused an outside‐to‐inside directed CO 2 gradient and generated a rapid biphasic intracellular acidification. The gradient of the acidifying gas was kept small to favour high affinity entry of CO 2 passing the membrane. All rates of acidification except that of the approach to physicochemical equilibrium of the uncatalysed reaction were restricted to the intracellular environment. Inhibition of carbonic anhydrase (CA) demonstrated that CO 2 ‐induced acidification required the catalytic activity of CA. Blockade of the function of either AQP1 (by HgCl 2 at 65 μM) or the HCO 3 − ‐Cl − transporter (by DIDS at 15 μM) completely prevented fast acidification. These data indicate that, at low chemical gradients for CO 2 , nearly the entire CO 2 transport across the red cell membrane is mediated by AQP1 and the HCO 3 − ‐Cl − transporter. Therefore, these proteins may function as high affinity sites for CO 2 transport across the erythrocyte membrane.