Volume-activated cation transport in dog red cells: detection and transduction of the volume stimulus

Evaluation of selected hematological, biochemical and oxidative stress parameters in stored canine CPDA-1 whole blood

Blood transfusions are mainly given to intensive care patients; therefore, additional complications that could arise from storage lesions in preserved blood should be avoided. It has been shown that human stored red blood cells are subject to changes that are considered to be a number of interdependent processes involving metabolic disarrangement and oxidative stress. The aim of our study was to determine alterations in selected hematological and biochemical parameters and to assess whether and when oxidative stress is a significant phenomenon in stored dog CPDA-1 whole blood. Ten ½ unit bags of whole blood donated from dogs and preserved with CPDA-1 (anticoagulant containing citrate, phosphate, dextrose and adenine) were stored for 5 weeks. Each week, a 9 ml sample was drawn aseptically to measure hematological parameters, selected metabolites, free hemoglobin content, osmotic fragility, antioxidant enzyme activity, total antioxidant capacity, malondialdehyde concentration and protein carbonyl content.

The results revealed an MCV decrease in the first week of storage and then a gradual increase; osmotic fragility decreased at that time and remained low throughout the study period. Leukodepletion became significant in the fourth week of storage. The free hemoglobin concentration continuously increased, with the greatest changes observed in the last two weeks of storage. The total antioxidant capacity changed in a reverse manner. Superoxide dismutase and glutathione peroxidase activities decreased from week 0 to week 3, and catalase activity tended to decrease over time. The highest malondialdehyde concentrations in blood supernatant were measured in the first week of storage, and the carbonyl concentration increased after 35 days.

Hematological changes and oxidative stress are already present in the first week of storage, resulting in depletion of the antioxidant system and subsequent accumulation of oxidation products as well as erythrocyte hemolysis, which are most pronounced at the end of the storage period.

Cation-leak stomatocytosis in standard schnauzers does not cosegregate with coding mutations in the RhAG, SLC4A1, or GLUT1 genes associated with human disease

Autosomal dominant overhydrated cation-leak stomatocytosis in humans has been associated with missense mutations in the erythroid membrane transport genes AE1, RhAG, and GLUT1. Syndromic stomatocytosis has been reported in three dog breeds, but stomatocytosis in Standard Schnauzers is usually asymptomatic, and is accompanied by minimal if any anemia. We have extended the evaluation of a cohort of schnauzers. We found that low-level stomatocytosis was accompanied by increased MCV and increased red cell Na content, and minimal or no reticulocytosis. Red cells from two affected dogs exhibited increased currents in on-cell patches measured in symmetrical NaCl solutions, but Na,K-ATPase and NKCC-mediated cation flux was minimal. Three novel coding polymorphisms found in canine RhAG cDNA and three novel polymorphisms found in canine SLC4A1 cDNA did not cosegregate with MCV or Na content. The GLUT1 cDNA sequence was normal. We conclude that unlike human overhydrated cation-leak stomatocytosis, stomatocytosis in this cohort of Standard Schnauzers is not caused by mutations in the genes encoding RhAG, SLC4A1, or GLUT1.

Apparent intermediate K conductance channel hyposmotic activation in human lens epithelial cells

This study explores the nature of K fluxes in human lens epithelial cells (LECs) in hyposmotic solutions. Total ion fluxes, Na-K pump, Cl-dependent Na-K-2Cl (NKCC), K-Cl (KCC) cotransport, and K channels were determined by 85Rb uptake and cell K (Kc) by atomic absorption spectrophotometry, and cell water gravimetrically after exposure to ouabain +/- bumetanide (Na-K pump and NKCC inhibitors), and ion channel inhibitors in varying osmolalities with Na, K, or methyl-d-glucamine and Cl, sulfamate, or nitrate. Reverse transcriptase polymerase chain reaction (RT-PCR), Western blot analyses, and immunochemistry were also performed. In isosmotic (300 mosM) media approximately 90% of the total Rb influx occurred through the Na-K pump and NKCC and approximately 10% through KCC and a residual leak. Hyposmotic media (150 mosM) decreased K(c) by a 16-fold higher K permeability and cell water, but failed to inactivate NKCC and activate KCC. Sucrose replacement or extracellular K to >57 mM, but not Rb or Cs, in hyposmotic media prevented Kc and water loss. Rb influx equaled Kc loss, both blocked by clotrimazole (IC50 approximately 25 microM) and partially by 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) inhibitors of the IK channel KCa3.1 but not by other K channel or connexin hemichannel blockers. Of several anion channel blockers (dihydro-indenyl)oxy]alkanoic acid (DIOA), 4-2(butyl-6,7-dichloro-2-cyclopentylindan-1-on-5-yl)oxybutyric acid (DCPIB), and phloretin totally or partially inhibited Kc loss and Rb influx, respectively. RT-PCR and immunochemistry confirmed the presence of KCa3.1 channels, aside of the KCC1, KCC2, KCC3 and KCC4 isoforms. Apparently, IK channels, possibly in parallel with volume-sensitive outwardly rectifying Cl channels, effect regulatory volume decrease in LECs.

Regulation of K-Cl cotransport: from function to genes

This review intends to summarize the vast literature on K-Cl cotransport (COT) regulation from a functional and genetic viewpoint. Special attention has been given to the signaling pathways involved in the transporter's regulation found in several tissues and cell types, and more specifically, in vascular smooth muscle cells (VSMCs). The number of publications on K-Cl COT has been steadily increasing since its discovery at the beginning of the 1980s, with red blood cells (RBCs) from different species (human, sheep, dog, rabbit, guinea pig, turkey, duck, frog, rat, mouse, fish, and lamprey) being the most studied model. Other tissues/cell types under study are brain, kidney, epithelia, muscle/smooth muscle, tumor cells, heart, liver, insect cells, endothelial cells, bone, platelets, thymocytes and Leishmania donovani. One of the salient properties of K-Cl-COT is its activation by cell swelling and its participation in the recovery of cell volume, a process known as regulatory volume decrease (RVD). Activation by thiol modification with N-ethylmaleimide (NEM) has spawned investigations on the redox dependence of K-Cl COT, and is used as a positive control for the operation of the system in many tissues and cells. The most accepted model of K-Cl COT regulation proposes protein kinases and phosphatases linked in a chain of phosphorylation/dephosphorylation events. More recent studies include regulatory pathways involving the phosphatidyl inositol/protein kinase C (PKC)-mediated pathway for regulation by lithium (Li) in low-K sheep red blood cells (LK SRBCs), and the nitric oxide (NO)/cGMP/protein kinase G (PKG) pathway as well as the platelet-derived growth factor (PDGF)-mediated mechanism in VSMCs. Studies on VSM transfected cells containing the PKG catalytic domain demonstrated the participation of this enzyme in K-Cl COT regulation. Commonly used vasodilators activate K-Cl COT in a dose-dependent manner through the NO/cGMP/PKG pathway. Interaction between the cotransporter and the cytoskeleton appears to depend on the cellular origin and experimental conditions. Pathophysiologically, K-Cl COT is altered in sickle cell anemia and neuropathies, and it has also been proposed to play a role in blood pressure control. Four closely related human genes code for KCCs (KCC1-4). Although considerable information is accumulating on tissue distribution, function and pathologies associated with the different isoforms, little is known about the genetic regulation of the KCC genes in terms of transcriptional and post-transcriptional regulation. A few reports indicate that the NO/cGMP/PKG signaling pathway regulates KCC1 and KCC3 mRNA expression in VSMCs at the post-transcriptional level. However, the detailed mechanisms of post-transcriptional regulation of KCC genes and of regulation of KCC2 and KCC4 mRNA expression are unknown. The K-Cl COT field is expected to expand further over the next decades, as new isoforms and/or regulatory pathways are discovered and its implication in health and disease is revealed.

Volume-sensitive K(+)/Cl(-) cotransport in rabbit erythrocytes. Analysis of the rate-limiting activation and inactivation events

The kinetics of activation and inactivation of K(+)/Cl(-) cotransport (KCC) have been measured in rabbit red blood cells for the purpose of determining the individual rate constants for the rate-limiting activation and inactivation events. Four different interventions (cell swelling, N-ethylmaleimide [NEM], low intracellular pH, and low intracellular Mg(2+)) all activate KCC with a single exponential time course; the kinetics are consistent with the idea that there is a single rate-limiting event in the activation of transport by all four interventions. In contrast to LK sheep red cells, the KCC flux in Mg(2+)-depleted rabbit red cells is not affected by cell volume. KCC activation kinetics were examined in cells pretreated with NEM at 0 degrees C, washed, and then incubated at higher temperatures. The forward rate constant for activation has a very high temperature dependence (E(a) approximately 32 kCal/mol), but is not affected measurably by cell volume. Inactivation kinetics were examined by swelling cells at 37 degrees C to activate KCC, and then resuspending at various osmolalities and temperatures to inactivate most of the transporters. The rate of transport inactivation increases steeply as cell volume decreases, even in a range of volumes where nearly all the transporters are inactive in the steady state. This finding indicates that the rate-limiting inactivation event is strongly affected by cell volume over the entire range of cell volumes studied, including normal cell volume. The rate-limiting inactivation event may be mediated by a protein kinase that is inhibited, either directly or indirectly, by cell swelling, low Mg(2+), acid pH, and NEM.

The role of phosphotriesterases in the detoxication of organophosphorus compounds

The enzymes that hydrolyze organophosphorus compounds are called phosphotriesterases. The presence of phosphotriesterases has been described in a variety of tissues. The physiological role of these enzymes is not known, although a clear correlation exists between the levels of phosphotriesterases and susceptibility of the species to the toxic effects of organophosphorus compounds. Thus, mammals that possess high levels of phosphotriesterases in serum and liver are more tolerant to the toxic effects of these compounds than birds and insects - these being species considered lacking of phosphotriesterases. Because most of these enzymes are not well characterized, they are usually differentiated according to their different patterns of response to activators and/ or inhibitors. Phosphotriesterases usually depend of divalent cations and therefore EDTA usually inhibits them. A peculiar EDTA-resistant phosphotriesterase has been described in serum albumin. The biotechnological and therapeutical applications of phosphotriesterases are currently subject to study.