| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CELLULAR |
1 School of Biological Sciences, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK
2 Department of Animal Physiology, Humboldt Universität zu Berlin, Philippstrasse 13, Abderhaldenhaus, D-10115 Berlin, Germany
3 Centre of Excellence in Evolutionary Genetics and Physiology, Department of Biology, University of Turku, FI-20014 Turku, Finland
The O2 dependence of ouabain-independent K+ transport mechanisms has been studied by unidirectional Rb+ flux analysis in crucian carp red blood cells (RBCs). The following observations suggest that O2 activates K+–Cl– cotransport (KCC) and deactivates Na+–K+–2Cl– cotransport (NKCC) in these cells via separate O2 sensors that differ in their O2 affinity. When O2 tension (PO2) at physiological pH 7.9 was increased from 0 to 1, 4, 21 or 100 kPa, K+ (Rb+) influx was increasingly inhibited, and at 100 kPa amounted to about 30% of the value at 0 kPa. This influx was almost completely Cl– dependent at high and low PO2, as shown by substituting Cl– with nitrate or methanesulphonate. K+ (Rb+) efflux showed a similar PO2 dependence as K+ (Rb+) influx, but was about 4–5 times higher over the whole PO2 range. The combined net free energy of transmembrane ion gradients favoured net efflux of ions for both KCC and NKCC mechanisms. The KCC inhibitor dihydroindenyloxyalkanoic acid (DIOA, 0.1 mM) abolished Cl–-dependent K+ (Rb+) influx at a PO2 of 100 kPa, but was only partially effective at low PO2 (0–1 kPa). At PO2 values between 0 and 4 kPa, K+ (Rb+) influx was further unaffected by variations in pH between 8.4 and 6.9, whereas the flux at 21 and 100 kPa was strongly reduced by pH values below 8.4. At pH 8.4, where K+ (Rb+) influx was maximal at high and low PO2, titration of K+ (Rb+) influx with the NKCC inhibitor bumetanide (1, 10 and 100 µM) revealed a highly bumetanide-sensitive K+ (Rb+) flux pathway at low PO2, and a relative bumetanide-insensitive pathway at high PO2. The bumetanide-sensitive K+ (Rb+) influx pathway was activated by decreasing PO2, with a PO2 for half-maximal activation (P50) not significantly different from the P50 for haemoglobin O2 binding. The bumetanide-insensitive K+ (Rb+) influx pathway was activated by increasing PO2 with a P50 significantly higher than for haemoglobin O2 binding. These results are relevant for the pathologically altered O2 sensitivity of RBC ion transport in certain human haemoglobinopathies.
(Received 3 May 2006;
accepted after revision 4 June 2006;
first published online 8 June 2006)
Corresponding author M. Berenbrink: School of Biological Sciences, The University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK. Email: michaelb{at}liv.ac.uk
This article has been cited by other articles:
|
|
 |
|
  H. Chu, A. Breite, P. Ciraolo, R. S. Franco, and P. S. Low Characterization of the deoxyhemoglobin binding site on human erythrocyte band 3: implications for O2 regulation of erythrocyte properties Blood, January 15, 2008; 111(2): 932 - 938. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Kristensen, P. Koldkjaer, M. Berenbrink, and T. Wang Oxygen-sensitive regulatory volume increase and Na transport in red blood cells from the cane toad, Bufo marinus J. Exp. Biol., July 1, 2007; 210(13): 2290 - 2299. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
