Published online 16 December 2009
Haematologica, Vol 95, Issue 2, 189-198 doi:10.3324/haematol.2009.010215
Copyright © 2010 by Ferrata Storti Foundation

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Red Cell Disorders

Cryohydrocytosis: increased activity of cation carriers in red cells from a patient with a band 3 mutation

Anna Bogdanova^1,*, Jeroen S. Goede^2,*, Erwin Weiss³, Nikolay Bogdanov¹, Poul Bennekou⁴, Ingolf Bernhardt³, Hans U. Lutz⁵

¹ Institute of Veterinary Physiology, and the Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
² University Hospital Zurich, Clinic of Hematology, Zurich, Switzerland
³ Saarland University, Laboratory of Biophysics, Saarbruecken, Germany
⁴ Department of Biology, University of Copenhagen, Denmark
⁵ ETH Zurich, Institute of Biochemistry, Zurich, Switzerland

Correspondence: Anna Bogdanova, Zurich Center for Integrative, Human Physiology, University of Zurich, Winterthurerstr. 260, CH 8057 Zurich, Switzerland., E-mail: annab{at}access.uzh.ch

Background: Cryohydrocytosis is an inherited dominant hemolytic anemia characterized by mutations in a transmembrane segment of the anion exchanger (band 3 protein). Transfection experiments performed in Xenopus oocytes suggested that these mutations may convert the anion exchanger into a non-selective cation channel. The present study was performed to characterize so far unexplored ion transport pathways that may render erythrocytes of a single cryohydrocytosis patient cation-leaky.

Design and Methods: Cold-induced changes in cell volume were monitored using ektacytometry and density gradient centrifugation. Kinetics, temperature and inhibitor-dependence of the cation and water movements in the cryohydrocytosis patient’s erythrocytes were studied using radioactive tracers and flame photometry. Response of the membrane potential of the patient’s erythrocyte membrane to the presence of ionophores and blockers of anion and cation channels was assessed.

Results: In the cold, the cryohydrocytosis patient’s erythrocytes swelled in KCl-containing, but not in NaCl-containing or KNO₃-containing media indicating that volume changes were mediated by an anion-coupled cation transporter. In NaCl-containing medium the net HOE-642-sensitive Na⁺/K⁺ exchange prevailed, whereas in KCl-containing medium swelling was mediated by a chloride-dependent K⁺ uptake. Unidirectional K⁺ influx measurements showed that the patient’s cells have abnormally high activities of the cation-proton exchanger and the K⁺,Cl^– co-transporter, which can account for the observed net movements of cations. Finally, neither chloride nor cation conductance in the patient’s erythrocytes differed from that of healthy donors.

Conclusions: These results suggest that cross-talk between the mutated band 3 and other transporters might increase the cation permeability in cryohydrocytosis.

Key words: red blood cells, cryohydrocytosis, Na⁺, K⁺, 2Cl^– co-transporter, cation carriers.