(Na,K)-ATPase and Ouabain binding in reticulocytes from dogs with high K and low K erythrocytes and their changes during maturation

Biological rhythms are correlated with Na+, K+-ATPase and oxidative stress biomarkers: A translational study on bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a chronic, severe, and multifactorial psychiatric disorder. Although biological rhythms alterations, sodium potassium pump (Na+, K+-ATPase) changes, and oxidative stress appear to play a critical role in the etiology and pathophysiology of BD, the inter-connection between them has not been described. Therefore this study evaluated the association between biological rhythms, Na+, K+-ATPase, and oxidative stress parameters in BD patients and the preclinical paradoxical sleep deprivation model (PSD).

METHODS

A translational study was conducted, including a case-control protocol with 36 BD and 46 healthy controls (HC). Subjects completed the Biological Rhythm Interview of Assessment in Neuropsychiatry (BRIAN). In addition, Erythrocyte Na+, K+-ATPase activity, and oxidative and nitrosative stress markers were assessed (4-hydroxynonenal [4-HNE], 8-isoprostane [8-ISO], thiobarbituric acid reactive substances [TBARS], carbonyl, 3-nitrotyrosine [3-nitro]). In the preclinical protocol, the same biomarkers were evaluated in the frontal cortex, hippocampus, and striatum from mice submitted to the PSD.

RESULTS

BD patients had a significantly higher total score of BRIAN versus HCs. Additionally, individuals with BD showed decreased Na+, K+-ATPase activity and increased oxidative stress parameters compared to HC without psychiatric disorders. This difference was driven by actively depressed BD subjects. The mice submitted to the PSD also demonstrated decreased Na+, K+-ATPase activity and increased oxidative stress parameters.

LIMITATIONS

BRIAN biological underpinning is less well characterized; We did not control for medication status; Sample size is limited; PSD it is not a true model of BD.

CONCLUSIONS

The present study found a significant correlation between Na+, K+-ATPase and oxidative stress with changes in biological rhythms, reinforcing the importance of these parameters to BD.

Structure and Function of Na,K-ATPase-The Sodium-Potassium Pump

Na,K-ATPase is an ubiquitous enzyme actively transporting Na-ions out of the cell in exchange for K-ions, thereby maintaining their concentration gradients across the cell membrane. Since its discovery more than six decades ago the Na-pump has been studied extensively and its vital physiological role in essentially every cell has been established. This article aims at providing an overview of well-established biochemical properties with a focus on Na,K-ATPase isoforms, its transport mechanism and principle conformations, inhibitors, and insights gained from crystal structures. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.

Cholesterol-binding protein TSPO2 coordinates maturation and proliferation of terminally differentiating erythroblasts

TSPO2 (translocator protein 2) is a transmembrane protein specifically expressed in late erythroblasts and has been postulated to mediate intracellular redistribution of cholesterol. We identified TSPO2 as the causative gene for the HK (high-K⁺) trait with immature red cell phenotypes in dogs and investigated the effects of the TSPO2 defects on erythropoiesis in HK dogs with the TSPO2 mutation and Tspo2 knockout (Tspo2^−/−) mouse models. Bone marrow–derived erythroblasts from HK dogs showed increased binucleated and apoptotic cells at various stages of maturation and shed large nuclei with incomplete condensation when cultured in the presence of erythropoietin, indicating impaired maturation and cytokinesis. The canine TSPO2 induces cholesterol accumulation in the endoplasmic reticulum and could thereby regulate cholesterol availability by changing intracellular cholesterol distribution in erythroblasts. Tspo2^−/− mice consistently showed impaired cytokinesis with increased binucleated erythroblasts, resulting in compensated anemia, and their red cell membranes had increased Na,K-ATPase, resembling the HK phenotype in dogs. Tspo2-deficient mouse embryonic stem cell–derived erythroid progenitor (MEDEP) cells exhibited similar morphological defects associated with a cell-cycle arrest at the G₂/M phase, resulting in decreased cell proliferation and had a depletion in intracellular unesterified and esterified cholesterol. When the terminal maturation was induced, Tspo2^−/− MEDEP cells showed delays in hemoglobinization; maturation-associated phenotypic changes in CD44, CD71, and TER119 expression; and cell-cycle progression. Taken together, these findings imply that TSPO2 is essential for coordination of maturation and proliferation of erythroblasts during normal erythropoiesis.

Pulmonary Circulation Transvascular Fluid Fluxes Do Not Change during General Anesthesia in Dogs

General anesthesia (GA) can cause abnormal lung fluid redistribution. Pulmonary circulation transvascular fluid fluxes (J_VA) are attributed to changes in hydrostatic forces and erythrocyte volume (EV) regulation. Despite the very low hydraulic conductance of pulmonary microvasculature it is possible that GA may affect hydrostatic forces through changes in pulmonary vascular resistance (PVR), and EV through alteration of erythrocyte transmembrane ion fluxes (_ionJ_VA). Furosemide (Fur) was also used because of its potential to affect pulmonary hydrostatic forces and _ionJ_VA. A hypothesis was tested that J_VA, with or without furosemide treatment, will not change with time during GA. Twenty dogs that underwent castration/ovariectomy were randomly assigned to Fur (n = 10) (4 mg/kg IV) or placebo treated group (Con, n = 10). Baseline arterial (BL) and mixed venous blood were sampled during GA just before treatment with Fur or placebo and then at 15, 30 and 45 min post-treatment. Cardiac output (Q) and pulmonary artery pressure (P_AP) were measured. J_VA and _ionJ_VA were calculated from changes in plasma protein, hemoglobin, hematocrit, plasma and whole blood ions, and Q. Variables were analyzed using random intercept mixed model (P < 0.05). Data are expressed as means ± SE. Furosemide caused a significant volume depletion as evident from changes in plasma protein and hematocrit (P < 0.001). However; Q, P_AP, and J_VA were not affected by time or Fur, whereas erythrocyte fluid flux was affected by Fur (P = 0.03). Furosemide also affected erythrocyte transmembrane K⁺ and Cl⁻, and transvascular Cl⁻ metabolism (P ≤ 0.05). No other erythrocyte transmembrane or transvascular ion fluxes were affected by time of GA or Fur. Our hypothesis was verified as J_VA was not affected by GA or ion metabolism changes due to Fur treatment. Furosemide and 45 min of GA did not cause significant hydrostatic changes based on Q and P_AP. Inhibition of Na⁺/K⁺/2Cl⁻ cotransport caused by Fur treatment, which can alter EV regulation and J_VA, was offset by the Jacobs Stewart cycle. The results of this study indicate that the Jacobs Stewart cycle/erythrocyte Cl⁻ metabolism can also act as a safety factor for the stability of lung fluid redistribution preserving optimal diffusion distance across the blood gas barrier.

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.

Red blood cell Na pump: Insights from species differences

The red blood cell membrane is specialized to exchange chloride and bicarbonate; usually the pH gradient, the chloride ratio, and the membrane potential are tightly coupled. We review the evidence that led to the ability to separately vary inside and outside pH in red cells. The effect of pH on Na pump activity and on the selectivity of the inside and the outside transport sites is reviewed. In red blood cells, at high pH, the outside site is not selective. An increase in protons leads to an increase in K(+) affinity, thus making the site more selective. The pK for this site is different in rats and humans; because of the high conservation of residues in these two species, there are only a few possible residues that can account for this difference. On the inside, work from unsided preparations suggests that, at high pH, the transport site is highly selective for Na(+). Once again, an increase in protons leads to an increase in K(+) affinity, but now the result is a less selective site. During their maturation, reticulocytes lose many membrane proteins. The type and fractional loss is species dependent. For example, most reticulocytes lose most of their Na pumps, retaining about 100 pumps per cell, but animals from the order Carnivora lose all their pumps. We review some of the evidence that PKC phosphorylation of N-terminus serines is responsible for endocytosis in other cell types and species variation in this region.

Suppressive effect of culture supernatant of erythrocytes and serum from dogs infected with Babesia gibsoni on the morphological maturation of canine reticulocytes in vitro

The present study evaluated the effects of infected culture supernatant of erythrocytes, fractionation of culture supernatant and serum from dogs infected with Babesia gibsoni (B. gibsoni) on the maturation of canine reticulocytes in vitro. The SDS-PAGE demonstrated that significantly broader bands were generated by both the infected culture supernatant of erythrocytes and the serum from dogs chronically infected with B. gibsoni. The culture supernatant of erythrocytes infected with B. gibsoni strongly suppressed the maturation of reticulocytes. Prior studies showed that chronically infected serum had inhibitory effects on both the maturation of reticulocytes and the canine pyrimidine 5'-nucleotidase subclass I and purine-specific 5'-nucleotidase activity. In addition, serum free infected culture supernatant of erythrocytes had an inhibitory effect on the morphological maturation of reticulocytes. These results suggest that infected serum and culture supernatant of erythrocytes might accumulate excess proteins and/or metabolites as a result of the inhibited maturation of reticulocytes and decreased activity of erythrocyte 5'-nucleotidase. Furthermore, the fractions observed at >150 kDa- and 150-70 kDa- in the infected culture supernatant and serum retarded the maturation of canine reticulocytes in vitro. The results obtained from the in vitro examinations, in the present study, suggested that B. gibsoni itself and/or its metabolites might release certain proteins in the infected culture supernatant and serum from infected dogs and as a result delay morphological maturation of canine reticulocytes.

Inhibition of Na,K-ATPase activity reduces Babesia gibsoni infection of canine erythrocytes with inherited high K, low Na concentrations

Babesia gibsoni multiplies well in canine red blood cells (RBCs) containing high concentrations of potassium (HK), reduced glutathione, and free amino acids as a result of an inherited high Na,K-ATPase activity, i.e., HK RBCs. To determine the role of Na,K-ATPase in the multiplication of B. gibsoni, the effect of ouabain on the proliferation of the parasites in HK RBCs was investigated. To determine the direct effect of ouabain on the parasites, the proliferation of the parasites in normal canine RBCs containing low potassium (LK) and high sodium concentrations, i.e., LK RBCs, which completely lack Na,K-ATPase activity, was observed. Ouabain at 0.1 mM significantly suppressed the multiplication of B. gibsoni in HK RBCs in vitro, whereas it had no effect on the parasites in LK RBCs. The results suggest that the multiplication of B. gibsoni in HK RBCs depends mainly on the presence of Na,K-ATPase in the cells. Therefore, the effects of ouabain on the intracellular cation and free amino acid composition of the HK RBCs were examined. In HK RBCs incubated with ouabain, a marked decrease in the concentration of potassium and an increase in sodium were observed, together with a decrease in the number of parasitized cells. These results suggest that the intracellular cation composition maintained by Na,K-ATPase might be advantageous to the parasites. Moreover, the concentrations of some free amino acids, i.e., asparagine, aspartate, glutamate, glutamine, glycine, and histidine, were markedly decreased in HK RBCs incubated with ouabain. Decreased concentrations of the free amino acids induced by inhibition of Na,K-ATPase seemed to affect the multiplication of B. gibsoni in HK RBCs. Based on these results, it is clear that the high Na,K-ATPase activity in HK RBCs contributes to the proliferation of B. gibsoni by maintaining high potassium and low sodium concentrations, as well as high concentrations of some free amino acids in the cells.

Serum from dogs Infected with Babesia gibsoni inhibits maturation of reticulocytes and erythrocyte 5'-nucleotidase activity in vitro

Erythrocyte 5'-nucleotidase is thought to be involved in the maturation of erythrocytes. In the present study, in vitro incubation of canine erythrocytes demonstrated that significant inhibition of 5'-nucleotidase activity occurred in the presence of serum from dogs infected with Babesia gibsoni, when the enzyme was assayed with cytidine 5'-monophosphate (5'-CMP) and inosine 5'-monophosphate (5'-IMP) as substrates. The multiplication of B. gibsoni in in vitro culture also resulted in a significant decrease in the enzyme activity of erythrocytes in the culture. Furthermore, the infected serum and 5'-CMP retarded the maturation of canine reticulocytes in vitro. These results suggested that nucleotides such as 5'-CMP and 5'-IMP might accumulate in young erythrocytes and/or serum in dogs infected with B. gibsoni as a result of decreased activity of erythrocyte 5'-nucleotidase, resulting in the delayed maturation of reticulocytes.

Rat erythrocytes express the anionic amino acid transport protein EAAC1

EAAC1 is a widely expressed protein which transports anionic amino acids in a Na(+)-dependent fashion. Rat erythrocytes have generally been thought to be impermeant to anionic amino acids. Utilizing immunoelectron microscopy, we have demonstrated the presence of EAAC1-immunoreactive protein within rat erythrocytes. Immunoblotting revealed the presence of an approximately 60-kDa protein, consistent with EAAC1, in erythrocyte membranes. Specificity was confirmed by peptide competition. In conclusion, EAAC1 is expressed in rat erythrocytes.

Babesia gibsoni: preferential multiplication in reticulocytes is related to the presence of mitochondria and a high concentration of adenosine 5'-triphosphate in the cells

To determine the cause of the predilection of Babesia gibsoni for reticulocytes, the parasites were cultivated with various types of reconstituted erythrocyte ghosts, which were prepared by resealing erythrocyte ghosts together with variously treated erythrocyte lysate, in vitro. The level of parasitemia in the culture with reconstituted reticulocyte ghosts containing untreated reticulocyte lysate was significantly higher than that in the culture with reconstituted normocyte (mature erythrocyte) ghosts containing untreated normocyte lysate. The removal of mitochondria from reconstituted reticulocyte ghosts by filtration or centrifugation resulted in decreased of parasitemia in those cultures. In contrast, when mitochondria from reticulocytes were loaded into reconstituted normocyte ghosts, the parasitemia in the ghosts loaded mitochondria was increased to the same level as that in reconstituted reticulocyte ghosts. Furthermore, the parsitemia in the culture with reconstituted normocyte ghosts was proportional to the concentration of adenosine 5'-triphosphate in the ghosts. These results suggested that mitochondria of reticulocytes might enhance the multiplication of B. gibsoni through the generation of adenosine 5'-triphosphate within the cells.

Some aspects of erythrocyte metabolism in a dog with polycythaemia vera

An 11-year-old female crossbred dog showed signs of polyuria, polydipsia, vomiting, posterior weakness and ataxia. Clinical and laboratory findings suggested the diagnosis of polycythaemia vera. The haematological values shown over a six-month period are presented. In four samples some aspects of erythrocyte function (glucose-6-phosphate dehydrogenase [G6PD] and pyruvate kinase [PK] activities, 2,3 diphosphoglycerate [2,3 DPG] concentration, osmotic fragility and intracellular sodium and potassium concentrations) were studied. Variable activities of G6PD and PK, probably related to different reticulocyte number, were detected together with normal osmotic fragility and intracellular sodium and potassium concentrations. 2,3 DPG concentration was higher than normal in all four samples. This could be interpreted as a response to a low tissue perfusion rather than a higher content of 2,3 DPG in red blood cells from the polycythaemic dog.

The cause of the predilection of Babesia gibsoni for reticulocytes

This study was conducted to determine why Babesia gibsoni replicates well in reticulocytes. First, B. gibsoni was cultivated in resealed erythrocyte ghosts loaded with either erythrocyte or reticulocyte lysate, and in reticulocyte ghosts loaded with either erythrocyte or reticulocyte lysate. The parasites multiplied well in the erythrocyte or reticulocyte ghosts loaded with reticulocyte lysate compared to the other resealed cells loaded with erythrocyte lysate. Second, the parasites were cultivated in erythrocytes in culture medium supplemented with either erythrocyte or reticulocyte lysate. The parasites multiplied better in reticulocyte lysate-containing cultures than in erythrocyte lysate-containing cultures. Finally, the parasites were cultivated in erythrocytes in culture medium supplemented with glutamate, aspartate, asparagine, glycine, isoleucine, proline, taurine or GSH, which were present in higher concentrations in reticulocytes than in erythrocytes. Supplementation of the culture medium with glutamate and GSH resulted in enhancement of the multiplication of the parasites, while the other amino acids did not enhance the multiplication. These results indicated that the high levels of the multiplication of B. gibsoni in reticulocytes are partly due to the high concentrations of glutamate and GSH in reticulocytes.

Inherited defects of sodium-dependent glutamate transport mediated by glutamate/aspartate transporter in canine red cells due to a decreased level of transporter protein expression

Canine red cells have a high affinity Na(+)/K(+)-dependent glutamate transporter. We herein demonstrate that this transport is mediated by the canine homologue of glutamate/aspartate transporter (GLAST), one of the glutamate transporter subtypes abundant in the central nervous system. We also demonstrate that GLAST is the most ubiquitous glutamate transporter among the transporter subtypes that have been cloned to date. The GLAST protein content was extremely reduced in variant red cells, low glutamate transport (LGlut) red cells characterized by an inherited remarkable decrease in glutamate transport activity. All LGluT dogs carried a missense mutation of Gly(492) to Ser (G492S) in either the heterozygous or homozygous state. The GLAST protein with G492S mutation was fully functional in glutamate transport in Xenopus oocytes. However, G492S GLAST exhibited a marked decrease in activity after the addition of cycloheximide, while the wild type showed no significant change, indicating that G492S GLAST was unstable compared with the wild-type transporter. Moreover, LGluT dogs, but not normal dogs, heterozygous for the G492S mutation showed a selective decrease in the accumulation of GLAST mRNA from the normal allele. Based on these findings, we conclude that a complicated heterologous combination of G492S mutation and some transcriptional defect contributes to the pathogenesis of the LGluT red cell phenotype.

Sodium/calcium exchange: its physiological implications

The Na+/Ca2+ exchanger, an ion transport protein, is expressed in the plasma membrane (PM) of virtually all animal cells. It extrudes Ca2+ in parallel with the PM ATP-driven Ca2+ pump. As a reversible transporter, it also mediates Ca2+ entry in parallel with various ion channels. The energy for net Ca2+ transport by the Na+/Ca2+ exchanger and its direction depend on the Na+, Ca2+, and K+ gradients across the PM, the membrane potential, and the transport stoichiometry. In most cells, three Na+ are exchanged for one Ca2+. In vertebrate photoreceptors, some neurons, and certain other cells, K+ is transported in the same direction as Ca2+, with a coupling ratio of four Na+ to one Ca2+ plus one K+. The exchanger kinetics are affected by nontransported Ca2+, Na+, protons, ATP, and diverse other modulators. Five genes that code for the exchangers have been identified in mammals: three in the Na+/Ca2+ exchanger family (NCX1, NCX2, and NCX3) and two in the Na+/Ca2+ plus K+ family (NCKX1 and NCKX2). Genes homologous to NCX1 have been identified in frog, squid, lobster, and Drosophila. In mammals, alternatively spliced variants of NCX1 have been identified; dominant expression of these variants is cell type specific, which suggests that the variations are involved in targeting and/or functional differences. In cardiac myocytes, and probably other cell types, the exchanger serves a housekeeping role by maintaining a low intracellular Ca2+ concentration; its possible role in cardiac excitation-contraction coupling is controversial. Cellular increases in Na+ concentration lead to increases in Ca2+ concentration mediated by the Na+/Ca2+ exchanger; this is important in the therapeutic action of cardiotonic steroids like digitalis. Similarly, alterations of Na+ and Ca2+ apparently modulate basolateral K+ conductance in some epithelia, signaling in some special sense organs (e.g., photoreceptors and olfactory receptors) and Ca2+-dependent secretion in neurons and in many secretory cells. The juxtaposition of PM and sarco(endo)plasmic reticulum membranes may permit the PM Na+/Ca2+ exchanger to regulate sarco(endo)plasmic reticulum Ca2+ stores and influence cellular Ca2+ signaling.

Incidence of dogs possessing red blood cells with high K in Japan and East Asia

The phenotype of high K (HK) red blood cells, which is an autosomal recessive, was found in dog groups from 10 of 13 breeds or populations in Japan. The incidence of HK was 26 to 38% in the San'in-Shiba, Shinshu-Shiba and Akita breeds, and the gene frequencies of HK ranged from 0.513 to 0.612. The highest incidence (42%) was found in the Jindo breed from Korea, and the gene frequency was 0.652. Two other groups from Korea also possessed this HK variation. However, although HK cells were not found in dogs from Taiwan, Indonesia, Mongolia and Sakhalin, Russia, the HK phenotype is clearly distributed now throughout Japan and Korea.

Heredity of red blood cells with high K and low glutathione (HK/LG) and high K and high glutathione (HK/HG) in a family of Japanese Shiba Dogs

Forty-two of 81 dogs from a family of Japanese Shiba dogs had red blood cells with a high K and a low Na concentration (HK). Of the HK dogs, 32 were high K and low glutathione (HK/LG) and 10 were high K and high glutathione (HK/HG). These variants were found in both males and females. The phenotype of HK was inherited in a recessive mode as reported earlier. A high incidence of HK/LG dogs was found in this family, and the phenotype was also inherited in a recessive mode. Glutamate (Glu) influx, which defines the cellular glutathione concentration, was lower in HK/LG cells than in HK/HG cells (in some cases extremely low). The fact that the red blood cells of HK/LG dogs have the two varying characteristics of a remaining Na, K-pump and low Glu transport suggests that 2 or more genes may be involved. Since an extremely low Glu influx was also found in normal low K and high Na (LK) red blood cells, the characteristic of low Glu transport also exists in LK cells. The phenotype of low Glu transport may also be inherited in a recessive mode. This family therefore had a very high incidence of homozygous recessive genes which control the phenotypes for the Na, K-pump and low Glu transport.

Loss of glucose transporters is an early event in differentiation of HD3 cells

The HD3 cell, a chicken erythroblast cell line infected with a temperature-sensitive avian erythroblastosis virus, becomes committed to differentiate to an erythrocyte upon temperature shift in presence of inducers. Before induction, the HD3 cell transports glucose and 2-deoxyglucose (2-DG). 3-O-methylglucose is poorly taken up. Upon induction of differentiation, glucose and 2-DG transport activity fall. Twenty-four hours postinduction, up to 75% of the glucose transport activity may disappear. By use of cDNA probes for chicken glucose transporters, two species of mRNA of 3.1 and 1.7 kb (equivalent to mammalian GLUT1 and GLUT3 mRNA, respectively) are detected. Both messages virtually disappear within 48 h after induction. Run-on assays show the cessation of synthesis of the corresponding RNAs parallel to the loss of glucose transport. In contrast to the glucose transporters, the nucleoside transporter level increases after induction of hematopoiesis. This developmental pattern is consistent with earlier studies showing that mature chicken erythrocytes have little glucose transport activity but retain appreciable levels of the nucleoside transporter and that nucleosides and glutamine provide major sources of oxidizable carbon compounds to sustain metabolism in circulating chicken erythrocytes.

Expression and loss of the transferrin receptor in growing and differentiating HD3 cells

During induced differentiation and maturation of HD3 cells (a chicken erythroblast cell line infected with a temperature-sensitive mutant of the avian erythroblastosis virus), the levels of transferrin receptor (TFR) and nucleoside transporter increase. Both these activities increase before elevated levels of hemoglobin are detected. Shortly after induction, as cellular TFR levels rise, a native-size TFR is detected in the cell-free culture medium, associated with an exosome fraction (100,000 xg pellet). Nucleoside transporter (measured as NBMPR-binding activity) is not increased in this pellet with induction. Previous studies have suggested that exosome formation in peripheral reticulocytes may be a significant route for loss of specific membrane proteins (Johnstone et al., 1991). Although the present experiments in HD3 cells do not address the quantitative importance of exosome formation, the studies suggest that exosome formation is an early event in commitment to the red cell lineage and is not a phenomenon restricted to the terminal stages of red cell maturation.

Effect of cell age and phenylhydrazine on the cation transport properties of rabbit erythrocytes

We studied the effect of cell age on the cation transport systems of rabbit erythrocytes by increasing the proportion of circulating young erythrocytes with either repeated bleeding or with phenylhydrazine (PHZ) treatment. We found that when the reticulocyte content of rabbit blood is increased by bleeding (from 1 to 40-50% of the circulating red cells), the response of the various transport pathways differs. The largest increase (fivefold) was found in the activity of K-Cl cotransport, which peaked 3 days after the last bleeding. The Na-K pump activity peaked at a similar time, but the % increase was twofold less than the K-Cl cotransport. There was a very small increase in the activity of the Na-Li exchange, whereas the Na-H exchange reached peak values 10 days after the last bleeding (twofold increase), when activities of K-Cl cotransport and Na-K pump had returned to almost normal levels. In vivo PHZ treatment resulted in anemia and marked reticulocytosis (80-90% of circulating cells). Transport rates were markedly increased (Na-K pump 9.6-fold, Na-H exchange 6.8-fold, Na-Li exchange 2.75-fold; K-Cl cotransport: 10-20-fold). When blood from PHZ-treated rabbits was incubated in vitro for 24-48 hours, red cell volume and K content decreased. This process was associated with a 70% reduction in the activity of the K-Cl cotransport after 24 hours and a 90% reduction after 48 hours. The activity of the other systems also declined and approached baseline values after 48 hours. Loss of transport activity was not affected by 10 microM E-64, whereas 10 mM methylamine reduced the inactivation of the Na-H exchange and of the Na-Li exchange. PHZ treatment of rabbit red cells in vitro resulted in marked increase of the K-Cl cotransport and inhibition of Na-K pump, Na-H exchange, and Na-Li exchange. These effects were abolished by DTT, with the exception of the Na-K pump inhibition, which was DTT insensitive. Thus both cell age and oxidative damage are important determinants of cation transport in rabbit red cells.

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

1. Carnivore red cells lose their Na/K pump capability as they develop from erythroblasts to reticulocytes to mature cells. They defend their fluid volume by utilizing the Ca/Na exchanger as a Na extrusion pump, the energy for which is ultimately derived from active Ca transport. 2. Swelling-induced [K-Cl] cotransport and shrinkage-induced Na/H exchange are regulated in a coordinated fashion in dog red cells. Circumstantial evidence points to a regulatory protein kinase-phosphatase system. 3. Dog red cells detect changes in their fluid volume, not by virtue of membrane distortion, but by alterations in the concentrations of cytoplasmic macromolecules induced by swelling or shrinkage.

Activation of ion transport pathways by changes in cell volume

Swelling-activated K+ and Cl- channels, which mediate RVD, are found in most cell types. Prominent exceptions to this rule include red cells, which together with some types of epithelia, utilize electroneutral [K(+)-Cl-] cotransport for down-regulation of volume. Shrinkage-activated Na+/H+ exchange and [Na(+)-K(+)-2 Cl-] cotransport mediate RVI in many cell types, although the activation of these systems may require special conditions, such as previous RVD. Swelling-activated K+/H+ exchange and Ca2+/Na+ exchange seem to be restricted to certain species of red cells. Swelling-activated calcium channels, although not carrying sufficient ion flux to contribute to volume changes may play an important role in the activation of transport pathways. In this review of volume-activated ion transport pathways we have concentrated on regulatory phenomena. We have listed known secondary messenger pathways that modulate volume-activated transporters, although the evidence that volume signals are transduced via these systems is preliminary. We have focused on several mechanisms that might function as volume sensors. In our view, the most important candidates for this role are the structures which detect deformation or stretching of the membrane and the skeletal filaments attached to it, and the extraordinary effects that small changes in concentration of cytoplasmic macromolecules may exert on the activities of cytoplasmic and membrane enzymes (macromolecular crowding). It is noteworthy that volume-activated ion transporters are intercalated into the cellular signaling network as receptors, messengers and effectors. Stretch-activated ion channels may serve as receptors for cell volume itself. Cell swelling or shrinkage may serve a messenger function in the communication between opposing surfaces of epithelia, or in the regulation of metabolic pathways in the liver. Finally, these transporters may act as effector systems when they perform regulatory volume increase or decrease. This review discusses several examples in which relatively simple methods of examining volume regulation led to the discovery of transporters ultimately found to play key roles in the transmission of information within the cell. So, why volume? Because it's functionally important, it's relatively cheap (if you happened to have everything else, you only need some distilled water or concentrated salt solution), and since it involves many disciplines of experimental biology, it's fun to do.

Several cation transporters and volume regulation in high-K dog red blood cells

Normal dog red blood cells lack the Na-K pump, and their cation composition is low K and high Na (LK). Recently, a dog was found with red blood cells containing high K and low Na concentrations (HK) due to the existence of the Na-K pump. In the present study, cation transport and volume regulation in HK cells were compared with those of LK cells. HK cells showed not only Rb influx through a Na-K pump, but also Rb influx through a Cl-dependent K transporter. The Rb influx rate through the Na-K pump was 0.65-1.44 mmol.l cells-1.h-1 in Cl and 1.75-2.24 mmol.l cells-1.h-1 in NO3, in HK cells, but only trace activities are found in LK cells. In HK cells, the Rb influx rate through Cl-dependent K transport was 0.36-0.96 mmol.l cells-1.h-1, and it was enhanced in swollen cells but vanished in shrunken cells. In LK cells, the transport was evident only in swollen cells. The original volume of swollen HK cells was restored by water extrusion promoted by Cl-dependent transport. The Na-Ca exchange transporter, which works as a volume regulator in LK cells, functioned in HK cells only when they were loaded with Na. Hence, the exchange transporter is latent in HK cells under physiological conditions. Moreover, the exchange transporter could restore the cell volume in swollen and Na-loaded HK cells. However, the volume in HK cells was still larger than that in LK cells, while the Na-Ca exchange transporter was working.(ABSTRACT TRUNCATED AT 250 WORDS)

Hereditary high-potassium erythrocytes with high Na, K-ATPase activity in Japanese shiba dogs

The sodium (Na) and potassium (K) concentrations and Na, K-ATPase activity were examined in erythrocytes from 24 Japanese shiba dogs and 79 dogs of 24 other breeds. Eleven of the shibas had erythrocytes with high K and low Na concentrations, together with high Na, K-ATPase activity (HK RBCs), while red cells from the remaining shibas and all of the other breeds examined showed low K and high Na concentrations, with no enzyme activity (LK RBCs). The concentration of reduced glutathione in HK RBCs was about five times that in LK RBCs. All the findings from HK shibas were in good agreement with those from HK mongrel dogs found in Japan previously. Since the shiba is a Japanese breed of dog, the results of the present study strongly suggest that the gene for HK RBCs may be inherent in dogs indigenous to Japan, particularly in shiba dogs.

Subcellular distribution of lipoxygenase products in rabbit reticulocyte membranes

Mitochondrial membranes and plasma membranes of rabbit reticulocytes contain oxygenated polyenoic fatty acids such as (9Z,11E)-(13S)-13-hydroxy-9,11-octadecadienoic acid, 9S and 9R isomers of (10E,12Z)-9-hydroxy-10,12-octadecadienoic acid and their all-E isomers. Furthermore (5Z,8Z,11Z,13E)-(15S)-15-hydroxy-5,8,11,13-icosa tetraenoic acid, 9- and 13-oxooctadecadienoic acid were detected as minor products. The chemical structure of these products has been identified by co-chromatography with authentic standards, by ultraviolet and infrared spectroscopy, and by gas chromatography/mass spectrometry of the native compounds and their hydrogenated derivatives. The oxygenated fatty acids originate most probably from the intracellular action of the erythroid arachidonate 15-lipoxygenase. In membranes of the mature erythrocyte only small amounts of hydroxy fatty acids were detected. Young peripheral reticulocytes contain more oxygenated polyenoic fatty acids in their membranes than older cells. In mixed cell populations, about 85% of the lipoxygenase products were found esterified to the membrane ester lipids, whereas 15% were associated as free hydroxy fatty acids with the membranes. The hydroxy fatty acid content of the mitochondrial membranes is more than threefold higher than that of the plasma membranes. The pattern of the products isolated from plasma membranes shows a high specificity with (9Z,11E)-(13S)-13-hydroxy-9,11-octadecadienoic acid as the main product. In contrast, the pattern found in the mitochondrial membranes was much more unspecific: a complex mixture of all positional and optical isomers was detected. The data presented indicate that the reticulocyte lipoxygenase in vivo acts on both plasma membranes and mitochondrial membranes. The results are discussed in the light of the involvement of the lipoxygenase in the breakdown of mitochondria and other organelles in reticulocytes during maturation.

Inherited persistence of immature type pyruvate kinase and hexokinase isozymes in dog erythrocytes

1. Red cell pyruvate kinase (EC 2.7.1.40) and hexokinase (EC 2.7.1.1) in high and low potassium (K) dogs were shown to exist as multiple forms which were separable by electrophoresis and ion-exchange chromatography. The R2-type pyruvate kinase, which was determined to be a young type enzyme in canine red cells, was shown to be the predominant form of pyruvate kinase in high K cells. 2. The M2-type pyruvate kinase, a prototype isozyme in erythroid cells, existed in high K dog erythrocytes as well as in high K and low K dog reticulocytes. 3. Isozyme analysis of high K red cell hexokinase also showed a profile similar to that obtained for low K reticulocytes. 4. These results seem to reflect the immaturity of high K erythrocytes, which suggest that an abnormal cell differentiation or maturation may occur at an early stage of erythroid cell proliferation in high K dogs.

Stability of [3H]ouabain binding to the (Na+ + K+)-ATPase solubilized with C12E8

The (Na+ + K+)-ATPase from dog kidney and partially purified membranes from HK dog erythrocytes were labeled with [3H]ouabain, solubilized with C12E8 and analyzed by HPLC through a TSK-GEL G3000SW column in the presence of C12E8, Mg2+, HPO4(2-) and glycerol at 20-23 degrees C. The peaks of [3H]ouabain bound to the enzyme from dog kidney and HK dog erythrocyte membranes corresponded to each other with apparent molecular weights of 470 000-490 000. In addition, these bindings of [3H]ouabain to the (Na+ + K+)-ATPase were observed to be stable at 20-23 degrees C for at least 18 h after the solubilization.