|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
Influence of Haemoglobin Conformation, Nitrite and Eicosanoids on K+ Transport Across the Carp Red Blood Cell Membrane
1 Institute of Biology, Odense University, DK-5230 Odense M, Denmark
The regulation of K+ transport across the red blood cell (RBC) membrane by haemoglobin (Hb) conformation was studied in carp, and the K+ transport mechanisms were identified. When a large proportion of Hb in the R quaternary structure was secured by oxygenation of blood at pH8.14, a net RBC K+ efflux was induced, which was accompanied by RBC shrinkage. This K+ efflux was resistant to ouabain and inhibited by furosemide and DIDS and by substitution of NO3- for Cl-, showing it to result from a K+/Cl- cotransport mechanism. Deoxygenation of the RBCs (Hb in T structure) eliminated the Cl--dependent K+ efflux and resulted in a net K+ uptake via the Na+/K+ pump. These changes were fully reversible. Nitrite-induced methaemoglobin formation in deoxygenated blood, which converts a large fraction of the T structure Hb into an R-like conformation, shifted the K+ uptake to a Cl--dependent K+ efflux similar to that seen in oxygenated cells. When the allosteric equilibrium between the R and T structures of Hb was gradually shifted towards the T state by decreases in pH, the Cl--dependent K+ efflux from oxygenated cells decreased. At pH7.52, where the Root effect caused a potent stabilisation of the T state, the K+ efflux was reversed to a net K+ uptake. A similar change was induced in methaemoglobin-containing deoxygenated blood, since low pH also favours a T-like conformation of metHb. The variable K+ fluxes could not be related to changes in membrane potential or pH but were always directly related to the experimental modulation of the relative proportions of R- and T-structure Hb. It is proposed that Hb conformation governs K+ movements via a different binding of T and R structures to integral membrane proteins, and that a large fraction of R-structure Hb triggers the Cl-dependent K+ efflux mechanism. Application of inhibitors and a substrate of prostaglandin and leukotriene synthesis did not influence the K+ efflux from oxygenated erythrocytes. However, a fraction of the K+ efflux from nitrite-treated deoxygenated cells was inhibited by nordihydroguaiaretic acid, suggesting that a slightly larger K+ efflux from these RBCs than from oxygenated RBCs was related to leukotriene production caused by nitrite entry. A much larger influx of nitrite to deoxygenated than to oxygenated RBCs was positively correlated with the distribution ratio of H+ and the membrane potential, supporting the view that nitrite primarily enters the cells via conductive transport. The physiological implications of the results are discussed.
Key words: K+ transport, red blood cells, haemoglobin conformation, oxygenation-dependent, ion transport, leukotrienes, prostaglandins
Accepted on June 11, 1992
This article has been cited by other articles:
|
|
 |
|
  F. B. Jensen and C. Agnisola Perfusion of the isolated trout heart coronary circulation with red blood cells: effects of oxygen supply and nitrite on coronary flow and myocardial oxygen consumption J. Exp. Biol., October 1, 2005; 208(19): 3665 - 3674. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. W Flatman Activation of ferret erythrocyte Na+-K+-2Cl- cotransport by deoxygenation J. Physiol., March 1, 2005; 563(2): 421 - 431. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. E. Weber, W. Voelter, A. Fago, H. Echner, E. Campanella, and P. S. Low Modulation of red cell glycolysis: interactions between vertebrate hemoglobins and cytoplasmic domains of band 3 red cell membrane proteins Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2004; 287(2): R454 - R464. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. C. Muzyamba, P. F. Speake, and J. S. Gibson Oxidants and regulation of K+-Cl- cotransport in equine red blood cells Am J Physiol Cell Physiol, October 1, 2000; 279(4): C981 - C989. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Gibson, A. Cossins, and J. Ellory Oxygen-sensitive membrane transporters in vertebrate red cells J. Exp. Biol., January 5, 2000; 203(9): 1395 - 1407. [Abstract] [PDF]
|
|
|
|
|
|
H. Guizouarn and R. Motais Swelling activation of transport pathways in erythrocytes: effects of Cl-, ionic strength, and volume changes Am J Physiol Cell Physiol, January 1, 1999; 276(1): C210 - C220. [Abstract] [Full Text] [PDF]
|
|
