The Properties of Red Blood Cells from Patients Heterozygous for HbS and HbC (HbSC Genotype).

Sickle cell disease (SCD) is one of the commonest severe inherited disorders, but specific treatments are lacking and the pathophysiology remains unclear. Affected individuals account for well over 250,000 births yearly, mostly in the Tropics, the USA, and the Caribbean, also in Northern Europe as well. Incidence in the UK amounts to around 12-15,000 individuals and is increasing, with approximately 300 SCD babies born each year as well as with arrival of new immigrants. About two thirds of SCD patients are homozygous HbSS individuals. Patients heterozygous for HbS and HbC (HbSC) constitute about a third of SCD cases, making this the second most common form of SCD, with approximately 80,000 births per year worldwide. Disease in these patients shows differences from that in homozygous HbSS individuals. Their red blood cells (RBCs), containing approximately equal amounts of HbS and HbC, are also likely to show differences in properties which may contribute to disease outcome. Nevertheless, little is known about the behaviour of RBCs from HbSC heterozygotes. This paper reviews what is known about SCD in HbSC individuals and will compare the properties of their RBCs with those from homozygous HbSS patients. Important areas of similarity and potential differences will be emphasised.Peer Reviewe

The role of WNK in modulation of KCl cotransport activity in red cells from normal individuals and patients with sickle cell anaemia

Abstract: Abnormal activity of red cell KCl cotransport (KCC) is involved in pathogenesis of sickle cell anaemia (SCA). KCC-mediated solute loss causes shrinkage, concentrates HbS, and promotes HbS polymerisation. Red cell KCC also responds to various stimuli including pH, volume, urea, and oxygen tension, and regulation involves protein phosphorylation. The main aim of this study was to investigate the role of the WNK/SPAK/OSR1 pathway in sickle cells. The pan WNK inhibitor WNK463 stimulated KCC with an EC50 of 10.9 ± 1.1 nM and 7.9 ± 1.2 nM in sickle and normal red cells, respectively. SPAK/OSR1 inhibitors had little effect. The action of WNK463 was not additive with other kinase inhibitors (staurosporine and N-ethylmaleimide). Its effects were largely abrogated by pre-treatment with the phosphatase inhibitor calyculin A. WNK463 also reduced the effects of physiological KCC stimuli (pH, volume, urea) and abolished any response of KCC to changes in oxygen tension. Finally, although protein kinases have been implicated in regulation of phosphatidylserine exposure, WNK463 had no effect. Findings indicate a predominant role for WNKs in control of KCC in sickle cells but an apparent absence of downstream involvement of SPAK/OSR1. A more complete understanding of the mechanisms will inform pathogenesis whilst manipulation of WNK activity represents a potential therapeutic approach

Hagfish (<i>Eptatretus stouti</i>) erythrocytes show minimal chloride transport activity

ABSTRACT Capnophorin (Band 3) is the major red cell transport protein, present in human erythrocyte membranes at 1 × 106 copies per cell. Under physiological conditions, the transporter is capable of moving 50 mol (Cl−/HCO3−) 1 cells−1 min−1 (Knauf, 1979), this high rate being necessary for carriage of CO2 in normal respiration (Wieth et al. 1982). In the present paper we demonstrate that, in contrast to the situation in all other vertebrate species studied except the lamprey (Ohnishi &amp; Asai, 1985), capnophorin activity in hagfish red cells is very limited, amounting to only 40 μmol Cl− transported 1 cells-1 min-1 at 11 °C, the environmental temperature of this species. Five experimental approaches were used to characterize this transporter in hagfish red cells: pH regulation in lightly buffered medium; 36C1− uptake; 36C1− efflux; effects of H2DIDS (dihydro-4,4-diisothiocyanostilbene 2,2-disulphonic acid), a specific capnophorin inhibitor (Knauf, 1979); and sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis (PAGE).</jats:p

Chapter 1 Ion Permeability of Membranes. From Lipid Bilayers to Biological Membranes

Although cells were first observed as early as in the 17th century, it is only over the last 100 years or so that our understanding of the permeability barrier imposed by the plasma membrane of cells started to emerge. The last 50 years, in particular, has seen a marked development in our knowledge of the characteristics of this barrier. The membrane itself comprises in the most part a bilayer of phospholipids, asymmetrically distributed, together with cholesterol and intrinsic and extrinsic proteins. Simple diffusion through the lipid phase can occur for lipid soluble moieties. In other cases, intrinsic membrane proteins provide pathways for solutes and water. Three types of pathways are described: channels, carriers, and pumps. What is known about flux through these proteins, together with their structure and function, is discussed-illustrated with reference to particularly significant pathways. The important part played by the red blood cell as a paradigm for membrane transport is explained. Existing gaps in our understanding of transport across membranes are emphasized. For example, how pumps like the quintessential membrane, the Na +-K + ATPase, operate remains unknown. In addition, the nature of the residual (or "leak") permeability, which remains when all such pathways are inhibited, is unclear. The residual permeability of biological membranes appears to be about 2 orders of magnitude greater than that of artificial lipid bilayers. An important caveat here is the existence of unknown pathways yet to be described. In this context, a novel permeability with characteristics of K +(Na +)/H + exchange is described which becomes manifest across the red blood cell membrane when cells are suspended in low ionic strength solution. Future discoveries will add to our understanding of membrane permeability. It is likely that the red blood cell will play an important part in this new chapter. © 2009 Elsevier Inc. All rights reserved