Elevated temperatures enhance KCCl activity in sickle cells

Does Plasma Inhibit the Activity of KCl Cotransport in Red Cells From LK Sheep?

Red cells from LK sheep represent an important paradigm for control of KCl cotransport activity, as well as being important to sheep erythroid function. A previous report (Godart et al., 1997) suggested that autologous plasma markedly inhibits red cell KCC activity and identified the presence of the bicarbonate/CO₂ buffer system as the probable cause. Findings were restricted, however, to red cells from patients with sickle cell disease (SCD) swollen anisotonically and carried out at a very high O₂ tension (c.700 mmHg). It was therefore important to investigate the generality of the effect described and whether it was also relevant to the two main stimuli for KCC activity encountered most often by circulating red cells in vivo - low pH in active muscle beds during exercise and high urea concentrations in the renal medulla during antidiuresis. Results confirm that inhibition was significant in response to anisotonic swelling with KCC activity in MOPS-buffered saline (MBS) vs. bicarbonate-buffered saline (BBS) and in MBS vs. plasma both reduced (by about 25 and 50%, respectively). By contrast, however, inhibition was absent at low pH and in high concentrations of urea. These findings suggest therefore that red cell KCC activity represents an important membrane permeability in vivo in red cells suspended in plasma. They are relevant, in particular, to sheep red cells, and may also be important by extension to those of other species and to the abnormal red cells found in human patients with SCD.

Molecular features and physiological roles of K+-Cl- cotransporter 4 (KCC4)

A K⁺-Cl^- cotransport system was documented for the first time during the mid-seventies in sheep and goat red blood cells. It was then described as a Na⁺-independent and ouabain-insensitive ion carrier that could be stimulated by cell swelling and N-ethylmaleimide (NEM), a thiol-reacting agent. Twenty years later, this system was found to be dispensed by four different isoforms in animal cells. The first one was identified in the expressed sequence tag (EST) database by Gillen et al. based on the assumption that it would be homologous to the Na⁺-dependent K⁺-Cl^- cotransport system for which the molecular identity had already been uncovered. Not long after, the three other isoforms were once again identified in the EST databank. Among those, KCC4 has generated much interest a few years ago when it was shown to sustain distal renal acidification and hearing development in mouse. As will be seen in this review, many additional roles were ascribed to this isoform, in keeping with its wide distribution in animal species. However, some of them have still not been confirmed through animal models of gene inactivation or overexpression. Along the same line, considerable knowledge has been acquired on the mechanisms by which KCC4 is regulated and the environmental cues to which it is sensitive. Yet, it is inferred to some extent from historical views and extrapolations.

Coronary artery ectasia in atherosclerotic coronary artery disease, inflammatory disorders, and sickle cell disease

Coronary artery ectasia (CAE) or aneurysm is usually defined as dilation ≥1.5-fold the normal vessel diameter. It has an incidence of 1.4-5.3% and is associated with a wide variety of etiologies-mainly congenital, atherosclerotic, and inflammatory ones. CAE is very common in sickle cell disease, and possibly sickle cell trait, with an incidence of 17.7%. It is likely related to the inflammatory process associated with hemoglobin S. Prognosis depends mainly on the underlying etiology. Atherosclerotic CAE does not carry additional risks compared to atherosclerotic coronary artery disease (ACAD) without ectasia. However, isolated CAE in the absence of ACAD carries an increased risk of myocardial infarction (MI) due to vasospasm, slower coronary blood flow, and thrombosis, typically within the dilated segments. Due to lack of studies and guidelines, management recommendations are based on personal experiences. Therapy should be tailored to each individual case after assessment of severity, history of complications, underlying etiology, and comorbidities. Treatment of underlying condition and avoidance of exacerbating factors are essential. Medical therapy in general may include antiplatelets, β-blockers, angiotensin-converting enzyme inhibitors statins, and dihydropyridine calcium channel blockers. In severe CAE or history of MI, the addition of anticoagulation therapy after assessing bleeding risk may be warranted. In acute MI, the large thrombus burden in the dilated segment makes the percutaneous approach very challenging. Aspiration attempts can result in distal thromboembolization. Survival is better in bypass grafting than with medical therapy. Nonetheless, bypass grafting does not improve survival in atherosclerotic CAE. Depending on the physical characteristics of aneurysm, different surgical approaches can be sought; however, the ideal one is unclear.