Erythrocyte ATP Research Articles

Influence of the course prescription of sodium succinate on functional state and general physical working ability of footballers organism during the training sessions

Pharmacological purpose of metabotropic preparations including burshtin acid and its derivative succinate sodium copes with the number of tasks the main of which is an activation of alternative ways of energoproduction at the work of submaximal and maximal force and preliminary training of the separate links of metabolism.The task of research is to ascertain changes that take place in functional state of sportsmen during long physical loadings and optimization of the work of cardiovascular system (CVS) and prophylaxis of psychical strains with the help of succinate sodium.Methods and organization of research. There were examined 84 sportsmen to ascertain changes that take place in the functional state of sportsmen during the long physical loadings and optimization of the work of CVS with the help of succinate sodium. Examinations took place during the training sessions (TS) in January, February and July 2012-2013 years.Results of research and its discussion. There was studied an efficiency of the course use of succinate sodium in footballers 100 mg 3 times a day during 14 days. Energetic supply of processes of intracellular homeostasis in erythrocytes realizes by means of ATP that is created in the process of glycolysis. According to the results of research after course prescription of succinate sodium in sportsmen the content of ATP in erythrocytes increased and an amount of ADP and AMP decreased. An improvement of general metabolic situation under an influence of succinate sodium was proved by the decrease of products of reactions of peroxidation in blood plasma of footballers.These results indicated an essential antiacidotic effect of the course use of succinate sodium by footballers after loading in anaerobic and glycolytic zone of intensity. At the same time there was ascertain in our research that the use of succinate sodium had a positive effect on the dynamics of lactate content during the processes of renewal after training in aerobic-anaerobic (85-90%intensity) and anaerobic (90-100% intensity) zones of preparation.The results of analyses of sportsmen who took succinate sodium had essentially lower level of enzymes activity than indicators of sportsmen who did not take this preparation. Indicators of aspartate aminotransferase (AST) and alaninaminotransferata (АLТ) were lower than at the beginning of TS. The received results indicated the stabilization of membranes of the cells of liver that consequently proved hepatoprotective effect of succinate. As under an influence of succinate sodium the speed of utilization of lactate accelerates so its course prescription favors an increase of oxygen flow capacity of arterial blood and the rise of transport capacity of O2 into tissues.The use of succinate sodium improves the work of adaptive mechanisms during the training and increases anti-stress effect. An assessment of the functional state of CVS on indicators of systolic and diastolic arterial pressure (AP syst, AP diast), pulse pressure (PP) and heart rate demonstrated that at the use of succinate sodium the aforesaid indicators of the footballers at the end of TS did not differ from the ones at the beginning of session.According to the results of research the course use of succinate sodium led to an essential growth of general force of cardiointervals spectrum. The spectral force increased in diapasons of the high (HF) and low frequencies (LF), and an indicator LF/HF decreased (84,9 % versus 139 % indicators of footballers who did not take succinate sodium) and was even lower than at the beginning of TS. Footballers who underwent the course prescription of succinate sodium noticed: an absence of signs of overstrain or overtraining; the rise of desire to train; the rise of the level of physical and psychical capacity for work and sport effectiveness.Conclusions. Metabotropic preparations are an important reserve for improvement the functional state of organism of sportsmen during the training in different zones of intensity. There was ascertained that course use of succinate sodium had a positive effect for metabolism, cytoarchitecture and functional abilities of erythrocytes. Normalization of indicators of the mean size of aggregate, indicator of aggregation and percent of unaggregated erythrocytes indicated an improvement of the state aggregative activity of erythrocytes, and the changes of rigidity index of erythrocytes indicated an improvement of its ability to deformation. The decrease of erythrocytes aggregation and normalization of its ability to deformation have a positive effect on rheological properties of blood and therefore lead to an improvement of blood circulation in microvessels and normalization of tissue metabolism.High physical activity and low fatigability; normal sleep and appetite; absence of transient attacks of head ache, unmotivated changes of mood, irritation and so on indicated an improvement of the general state of sportsmen who underwent the course prescription of succinate sodium

CD73 and AMPD3 deficiency enhance metabolic performance via erythrocyte ATP that decreases hemoglobin oxygen affinity.

Erythrocytes are the key target in 5′-AMP induced hypometabolism. To understand how regulation of endogenous erythrocyte AMP levels modulates systemic metabolism, we generated mice deficient in both CD73 and AMPD3, the key catabolic enzymes for extracellular and intra-erythrocyte AMP, respectively. Under physiological conditions, these mice displayed enhanced capacity for physical activity accompanied by significantly higher food and oxygen consumption, compared to wild type mice. Erythrocytes from Ampd3−/− mice exhibited higher half-saturation pressure of oxygen (p50) and about 3-fold higher levels of ATP and ADP, while they maintained normal 2,3-bisphosphoglycerate (2,3-BPG), methemoglobin levels and intracellular pH. The affinity of mammalian hemoglobin for oxygen is thought to be regulated primarily by 2,3-BPG levels and pH (the Bohr effect). However, our results show that increased endogenous levels of ATP and ADP, but not AMP, directly increase the p50 value of hemoglobin. Additionally, the rise in erythrocyte p50 directly correlates with an enhanced capability of systemic metabolism.

Enhanced eryptosis following juglone exposure.

Juglone, a quinone isolated from Juglans mandshurica Maxim, has previously been shown to be effective against malignancy. The effect is at least partially due to stimulation of suicidal death or apoptosis of tumour cells. On the other hand, juglone has been shown to counteract apoptosis, for example, of neurons. In analogy to apoptosis of nucleated cells, erythrocytes may enter eryptosis, a suicidal death characterized by cell shrinkage and breakdown of phosphatidylserine asymmetry of the cell membrane with phosphatidylserine exposure at the erythrocyte surface. Stimulators of eryptosis include increase in cytosolic Ca(2+) activity [(Ca(2+) )i]. This study explored whether juglone stimulates eryptosis. To this end, erythrocyte volume was estimated from forward scatter, phosphatidylserine exposure at the erythrocyte surface from FITC annexin V binding, ceramide abundance from binding of fluorescent antibodies in flow cytometry and cytosolic ATP with a luciferin-luciferase-based assay. As a result, a 24-hr exposure of human erythrocytes to juglone (5 μM) significantly decreased erythrocyte forward scatter. Juglone (1-5 μM) significantly increased the percentage of annexin V binding cells. Juglone (5 μM) significantly increased ceramide abundance at the erythrocyte surface and decreased erythrocyte ATP concentration. The effect of juglone (10 μM) on annexin V binding was slightly but significantly blunted by removal of extracellular Ca(2+) and by addition of protein kinase C (PKC) inhibitor staurosporine (1 μM). In conclusion, juglone stimulates suicidal erythrocyte death or eryptosis at least in part by upregulation of ceramide abundance, energy depletion and activation of PKC.

Remodelling of the erythrocyte cytoskeleton during P. falciparum merozoite invasion

Background Red blood cells are remarkably resilient, flexible and dynamic structures. These properties are required for their passage through small capillaries and are imparted by the cytoskeleton, a network of proteins that underlies and links to the cell membrane. To successfully invade, the blood stage malaria parasite must induce drastic changes to the structure of the target erythrocyte, including the formation of a tight junction and a new cellular compartment, the parasitophorous vacuole. These key modifications involve the infolding of the red blood cell membrane, membrane fusion and fission events and the secretion of parasite proteins into the host. While detailed cellular descriptions of merozoite invasion have been achieved over the past few decades, comparatively little is known about the molecular basis of how the host cell responds to parasite entry. It has long been suggested that erythrocyte ATP and a kinase are required for successful invasion, while more recently a role for a host-cell actin polymerisation in invasion has been posited. We hypothesize that to invade, merozoites interface with endogenous erythrocyte pathways that regulate membrane and cytoskeletal remodelling, and here present cellular and molecular data on the host factors involved in facilitating merozoite invasion.

Stimulation of Erythrocyte Death by Phloretin

Background: Phloretin, a natural component of apples, pears and strawberries, has previously been shown to stimulate apoptosis of nucleated cells. Erythrocytes may similarly enter suicidal death or eryptosis, which is characterized by cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane with phosphatidylserine translocation to the erythrocyte surface. Stimulators of eryptosis include increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i), ceramide, ATP depletion, and activation of protein kinase C (PKC) as well as p38 mitogen activated protein kinase (p38 kinase). Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin V binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, and ceramide abundance from binding of specific antibodies. Results: A 48 h exposure of human erythrocytes to phloretin significantly increased the percentage of annexin-V-binding cells (≥100 µM) without significantly influencing forward scatter. Phloretin did not significantly modify [Ca²⁺]_i and the stimulation of annexin-V-binding by phloretin (300 µM) did not require presence of extracellular Ca²⁺. Phloretin did not significantly modify erythrocyte ATP levels, and the effect of phloretin on annexin-V-binding was not significantly altered by PKC inhibitor staurosporine (1 µM) or p38 kinase inhibitor SB2203580 (2 µM). However, phloretin significantly increased the ceramide abundance at the cell surface. Conclusions: Phloretin stimulates phospholipid scrambling of the erythrocyte cell membrane, an effect at least partially due to up-regulation of ceramide abundance.

Kinetics of extracellular ATP in mastoparan 7-activated human erythrocytes

BackgroundThe peptide mastoparan 7 (MST7) stimulated ATP release in human erythrocytes. We explored intra- and extracellular processes governing the time-dependent accumulation of extracellular ATP (i.e., ATPe kinetics). MethodsHuman erythrocytes were treated with MST7 in the presence or absence of two blockers of pannexin 1. ATPe concentration was monitored by luciferin–luciferase based real-time luminometry. ResultsExposure of human erythrocytes to MST7 led to an acute increase in [ATPe], followed by a slower increase phase. ATPe kinetics reflected a strong activation of ATP efflux and a low rate of ATPe hydrolysis by ectoATPase activity. Enhancement of [ATPe] by MST7 required adhesion of erythrocytes to poly-D-lysin-coated coverslips, and correlated with a 31% increase of cAMP and 10% cell swelling. However, when MST7 was dissolved in a hyperosmotic medium to block cell swelling, ATPe accumulation was inhibited by 49%.Erythrocytes pre-exposure to 10μM of either carbenoxolone or probenecid, two blockers of pannexin 1, exhibited a partial reduction of ATP efflux.Erythrocytes from pannexin 1 knockout mice exhibited similar ATPe kinetics as those of wild type mice erythrocytes exposed to pannexin 1 blockers. ConclusionsMST7 induced release of ATP required either cell adhesion or strong activation of cAMP synthesis. Part of this release required cell swelling. Kinetic analysis and a data driven model suggested that ATP efflux is mediated by two ATP conduits displaying different kinetics, with one conduit being fully blocked by pannexin 1 blockers. General significanceKinetic analysis of extracellular ATP accumulation from human erythrocytes and potential effects on microcirculation.

Kinetics of extracellular ATP in mastoparan 7-activated human erythrocytes

Kinetics of extracellular ATP in mastoparan 7-activated human erythrocytes

AMPD3‐deficient mice exhibit increased erythrocyte ATP levels but anemia not improved due to PK deficiency

AMP deaminase (AMPD) catalyzes AMP to IMP and plays an important role in energy charge and nucleotide metabolism. Human AMPD3 deficiency is a type of erythrocyte-specific enzyme deficiency found in individuals without clinical symptoms, although an increased level of ATP in erythrocytes has been reported. To better understand the physiological and pathological roles of AMPD3 deficiency, we established a line of AMPD3-deficient [A3(-/-)] mice. No AMPD activity and a high level of ATP were observed in erythrocytes of these mice, similar to human RBC-AMPD3 deficiency, while other characteristics were unremarkable. Next, we created AMPD3 and pyruvate kinase (PK) double-deficient [PKA(-/-,-/-)] mice by mating A3(-/-) mice with CBA-Pk-1slc/Pk-1slc mice [PK(-/-)], a spontaneous PK-deficient strain showing hemolytic anemia. In PKA(-/-,-/-) mice, the level of ATP in red blood cells was increased 1.5 times as compared to PK(-/-) mice, although hemolytic anemia in those animals was not improved. In addition, we observed osmotic fragility of erythrocytes in A3(-/-) mice under fasting conditions. In contrast, the ATP level in erythrocytes was elevated in A3(-/-) mice as compared to the control. In conclusion, AMPD3 deficiency increases the level of ATP in erythrocytes, but does not improve anemia due to PK deficiency and leads to erythrocyte dysfunction.

Effect of Aconiti Lateralis Radix Praeparata and Taraxaci Herba on Chinese medicine signs and symptoms of urethane-induced lung cancer in mice

To study Chinese medicine (CM) signs and symptoms of urethane-induced lung cancer in mice, and observe the effect of Aconiti Lateralis Radix Praeparata and Taraxaci Herba on symptoms in mice and tumor progress. The mice were intraperitoneally injected with urethane twice a week for consecutively five weeks to establish a lung cancer model. The changes in their appearance, body temperature and auricle microcirculation were observed in carcinogenic process. CM signs and symptoms of urethane-induced lung cancer in mice were evaluated with energy metabolism, erythrocytic ATP emzymatic activity and hemorrheological index. During the tumor model was induced, Aconiti Lateralis Radix Praeparata and Taraxaci Herba were used to treat the mice and observe their effect on symptoms in mice and tumor progress. During urethane was used to induce lung cancer, the mice had gradually become chill, lazy, hunched, with reduction in temperature, cyanosis in auricle and tail. Meanwhile, their energy metabolism and erythrocytic ATP enzymatic activity reduced, whereas their whole blood viscosity and erythrocytic aggregate index increased. Taraxaci Herba showed an effect on enhancing above symptoms and signs but had no effect on tumor progress. Aconiti Lateralis Radix Praeparata showed an effect on reducing above symptoms and signs and preventing tumor progress. Mice with urethane-induced lung cancer show CM signs and symptoms of congealing cold with blood stasis. The treatment with Aconiti Lateralis Radix Praeparata can alleviate symptoms and signs in mice and prevent tumor progress.

Transfusion of fresh but not old stored blood reduces infarct size and improves cardiac function after acute myocardial infarction in anemic rats*

We recently demonstrated that transfusion of fresh blood to 100 g/L hemoglobin in anemic animals offers cardioprotection after acute myocardial infarction. The objective of this study was to compare the cardioprotective effects of fresh vs. stored blood when transfused in anemic rats after acute myocardial infarction. Randomized animal study. University laboratory. Male Sprague-Dawley rats weighing 200-300 g. Myocardial infarction was induced by coronary artery ligation in 49 male Sprague-Dawley rats weighing 200-300 g, 38 of which were anemic (80-90 g/L) and 11 with normal hemoglobin levels. Anemic animals were randomized to receive fresh blood (within 4 hrs), stored blood (7 days), or no transfusion immediately after myocardial infarction. At 24 hrs after myocardial infarction, cardiac function, infarct size, and apoptosis were determined. Erythrocyte ATP, 2,3-DPG, hemoglobin, and free hemoglobin levels in the supernatant were determined. Transfusion with fresh but not stored blood significantly decreased infarct size and myocardial apoptosis in anemic rats when compared to anemic animals not undergoing transfusion. Cardiac function and survival were significantly improved in the anemic animals undergoing fresh blood transfusion compared to control anemic animals. Analysis of stored red blood cells showed reductions of intracellular ATP and 2,3-DPG levels and free hemoglobin was increased in the supernatant. The prolonged storage of blood negates the beneficial effects of fresh blood transfusion, which include reductions in infarct size and myocardial apoptosis, and improvements in cardiac function and short-term survival after acute myocardial infarction in this animal model.

Temperature‐dependent release of ATP from human erythrocytes: mechanism for the control of local tissue perfusion

Human limb muscle and skin blood flow increases significantly with elevations in temperature, possibly through physiological processes that involve temperature-sensitive regulatory mechanisms. Here we tested the hypothesis that the release of the vasodilator ATP from human erythrocytes is sensitive to physiological increases in temperature both in vitro and in vivo, and examined potential channel/transporters involved. To investigate the source of ATP release, whole blood, red blood cells (RBCs), plasma and serum were heated in vitro to 33, 36, 39 and 42°C. In vitro heating augmented plasma or ‘bathing solution’ ATP in whole blood and RBC samples, but not in either isolated plasma or serum samples. Heat-induced ATP release was blocked by niflumic acid and glibenclamide, but was not affected by inhibitors of nucleoside transport or anion exchange. Heating blood to 42°C enhanced (P < 0.05) membrane protein abundance of cystic fibrosis transmembrane conductance regulator (CFTR) in RBCs. In a parallel in vivo study in humans exposed to whole-body heating at rest and during exercise, increases in muscle temperature from 35 to 40°C correlated strongly with elevations in arterial plasma ATP (r2 = 0.91; P = 0.0001), but not with femoral venous plasma ATP (r2 = 0.61; P = 0.14). In vitro, however, the increase in ATP release from RBCs was similar in arterial and venous samples heated to 39°C. Our findings demonstrate that erythrocyte ATP release is sensitive to physiological increases in temperature, possibly via activation of CFTR-like channels, and suggest that temperature-dependent release of ATP from erythrocytes might be an important mechanism regulating human limb muscle and skin perfusion in conditions that alter blood and tissue temperature.

Toward a Multiscale Description of Microvascular Flow Regulation: O2-Dependent Release of ATP from Human Erythrocytes and the Distribution of ATP in Capillary Networks

Integration of the numerous mechanisms that have been suggested to contribute to optimization of O2 supply to meet O2 need in skeletal muscle requires a systems biology approach which permits quantification of these physiological processes over a wide range of length scales. Here we describe two individual computational models based on in vivo and in vitro studies which, when incorporated into a single robust multiscale model, will provide information on the role of erythrocyte-released ATP in perfusion distribution in skeletal muscle under both physiological and pathophysiological conditions. Healthy human erythrocytes exposed to low O2 tension release ATP via a well characterized signaling pathway requiring activation of the G-protein, Gi, and adenylyl cyclase leading to increases in cAMP. This cAMP then activates PKA and subsequently CFTR culminating in ATP release via pannexin 1. A critical control point in this pathway is the level of cAMP which is regulated by pathway-specific phosphodiesterases. Using time constants (~100 ms) that are consistent with measured erythrocyte ATP release, we have constructed a dynamic model of this pathway. The model predicts levels of ATP release consistent with measurements obtained over a wide range of hemoglobin O2 saturations (sO2). The model further predicts how insulin, at concentrations found in pre-diabetes, enhances the activity of PDE3 and reduces intracellular cAMP levels leading to decreased low O2-induced ATP release from erythrocytes. The second model, which couples O2 and ATP transport in capillary networks, shows how intravascular ATP and the resulting conducted vasodilation are affected by local sO2, convection and ATP degradation. This model also predicts network-level effects of decreased ATP release resulting from elevated insulin levels. Taken together, these models lay the groundwork for investigating the systems biology of the regulation of microvascular perfusion distribution by erythrocyte-derived ATP.

Homeostasis of Extracellular ATP in Human Erythrocytes

We explored the intra- and extracellular processes governing the kinetics of extracellular ATP (ATPe) in human erythrocytes stimulated with agents that increase cAMP. Using the luciferin-luciferase reaction in off-line luminometry we found both direct adenylyl cyclase activation by forskolin and indirect activation through β-adrenergic stimulation with isoproterenol-enhanced [ATP]e in a concentration-dependent manner. A mixture (3V) containing a combination of these agents and the phosphodiesterase inhibitor papaverine activated ATP release, leading to a 3-fold increase in [ATP]e, and caused increases in cAMP concentration (3-fold for forskolin + papaverine, and 10-fold for 3V). The pannexin 1 inhibitor carbenoxolone and a pannexin 1 blocking peptide ((10)Panx1) decreased [ATP]e by 75-84%. The residual efflux of ATP resulted from unavoidable mechanical perturbations stimulating a novel, carbenoxolone-insensitive pathway. In real-time luminometry experiments using soluble luciferase, addition of 3V led to an acute increase in [ATP]e to a constant value of ∼1 pmol × (10(6) cells)(-1). A similar treatment using a surface attached luciferase (proA-luc) triggered a rapid accumulation of surface ATP levels to a peak concentration of 2.4 pmol × (10(6) cells)(-1), followed by a slower exponential decay (t(&frac12;) = 3.7 min) to a constant value of 1.3 pmol × (10(6) cells)(-1). Both for soluble luciferase and proA-luc, ATP efflux was fully blocked by carbenoxolone, pointing to a 3V-induced mechanism of ATP release mediated by pannexin 1. Ecto-ATPase activity was extremely low (∼28 fmol × (10(6) cells min)(-1)), but nevertheless physiologically relevant considering the high density of erythrocytes in human blood.

The Rho kinase inhibitor Y-27632 increases erythrocyte deformability and low oxygen tension-induced ATP release

Low oxygen (O(2)) tension and mechanical deformation are stimuli for ATP release from erythrocytes. It has been shown previously that rabbit erythrocytes made less deformable with diamide, a thiol cross-linking agent, release less ATP in response to low O(2) tension, suggesting a link between these two stimuli. In nonerythroid cells, activation of the Rho/Rho kinase signaling pathway has been reported to decrease cell deformability by altering Rho kinase-dependent cytoskeleton-protein interactions. We investigated the hypothesis that the Rho kinase inhibitor Y-27632 would increase erythrocyte deformability and thereby increase low O(2) tension-induced ATP release from erythrocytes. Here we show that Y-27632 (1 μM) increases erythrocyte deformability (5%) and increases low O(2) tension-induced ATP release (203%) from healthy human erythrocytes. In addition, we found that, when erythrocytes were made less deformable by incubation with diamide (100 μM), Y-27632 restored both deformability and low O(2) tension-induced ATP release to levels similar to those measured in the absence of diamide. These findings suggest that the Rho kinase inhibitor Y-27632 is able to reverse the diamide-induced decrease in erythrocyte deformability and rescue low O(2) tension-induced ATP release. These results further support a link between erythrocyte deformability and ATP release in response to low O(2) tension.

The Effect of Aspirin on Red Cell Electrolyte, ATP Levels and Glucose Utilization in Rats

Wistar rats were fed chow supplemented with 1% (w/w) aspirin for one month. At 3, 7, 14, 21 and 30 days of treatment, heparinized blood was collected. ATP, Na+, K+ levels, glucose utilization of erythrocytes and inorganic phosphate, Na+, K+, salicylate levels of plasma were determined. Erythrocyte ATP and plasma phosphate levels were decreased following aspirin treatment. ATP decrement caused erythrocyte K+ level to diminish significantly. Plasma Na+ and K+ levels were not effected by aspirin treatment. In addition, the decrease in ATP levels induced erythrocyte glucose utilization. It was concluded that the therapeutic dose of aspirin in man, gave rise to a decrease in the energy production and an impairment of energy utilizing events in erythrocytes in rats (the therapeutic serum aspirin concentration in man is 25-40 mg dL−1).

Beauvericin induced erythrocyte cell membrane scrambling

Beauvericin is a mycotoxin with antiviral, antibacterial, nematicidal, insecticidal, cytotoxic, and apoptotic activity. Similar to nucleated cells erythrocytes may undergo suicidal death or eryptosis, which is characterized by cell shrinkage and phosphatidylserine exposure at the erythrocyte surface. Eryptosis may be triggered by energy depletion leading to increase of cytosolic Ca 2+ activity. The present study thus explored whether beauvericin is able to trigger eryptosis and influence eryptosis following energy depletion. Cell membrane scrambling was estimated from binding of annexin V to phosphatidylserine at the erythrocyte surface, cell volume from forward scatter in FACS analysis, cytosolic Ca 2+ concentration from Fluo3 fluorescence, cytosolic ATP concentration from a luciferase-assay and ion channel activity with whole cell patch clamp. Exposure to beauvericin (≥5 μM) significantly decreased erythrocyte ATP concentration and increased cytosolic Ca 2+ concentration as well as annexin V-binding. The effect of beauvericin on annexin V binding was significantly blunted by removal of extracellular Ca 2+. Glucose depletion (48 h) was followed by, increase of Fluo3 fluorescence, decrease of forward scatter and increase of annexin V-binding. Beauvericin (≥1 μM) augmented the effect of glucose withdrawal on Fluo3 fluorescence and annexin V-binding, but significantly blunted the effect of glucose withdrawal on forward scatter, an effect paralleled by inhibition of Ca 2+ activated K + channels. The present observations disclose novel effects of beauvericin, i.e. stimulation of Ca 2+ entry with subsequent cell membrane scrambling and inhibition of Ca 2+ activated K + channels with blunting of cell shrinkage.

Homeostasis of Extracellular ATP in Human Erythrocytes

Homeostasis of Extracellular ATP in Human Erythrocytes

Erythrocyte-dependent regulation of human skeletal muscle blood flow: role of varied oxyhemoglobin and exercise on nitrite, S-nitrosohemoglobin, and ATP

The erythrocyte is proposed to play a key role in the control of local tissue perfusion via three O(2)-dependent signaling mechanisms: 1) reduction of circulating nitrite to vasoactive NO, 2) S-nitrosohemoglobin (SNO-Hb)-dependent vasodilatation, and 3) release of the vasodilator and sympatholytic ATP; however, their relative roles in vivo remain unclear. Here we evaluated each mechanism to gain insight into their roles in the regulation of human skeletal muscle blood flow during hypoxia and hyperoxia at rest and during exercise. Arterial and femoral venous hemoglobin O(2) saturation (O(2)Hb), plasma and erythrocyte NO and ATP metabolites, and leg and systemic hemodynamics were measured in 10 healthy males exposed to graded hypoxia, normoxia, and graded hyperoxia both at rest and during submaximal one-legged knee-extensor exercise. At rest, leg blood flow and NO and ATP metabolites in plasma and erythrocytes remained unchanged despite large alterations in O(2)Hb. During exercise, however, leg and systemic perfusion and vascular conductance increased in direct proportion to decreases in arterial and venous O(2)Hb (r(2) = 0.86-0.98; P = 0.01), decreases in venous plasma nitrite (r(2) = 0.93; P < 0.01), increases in venous erythrocyte nitroso species (r(2) = 0.74; P < 0.05), and to a lesser extent increases in erythrocyte SNO (r(2) = 0.59; P = 0.07). No relationship was observed with plasma ATP (r(2) = 0.01; P = 0.99) or its degradation compounds. These in vivo data indicate that, during low-intensity exercise and hypoxic stress, but not hypoxic stress alone, plasma nitrite consumption and formation of erythrocyte nitroso species are associated with limb vasodilatation and increased blood flow in the human skeletal muscle vasculature.

Divergent effects of low-O2tension and iloprost on ATP release from erythrocytes of humans with type 2 diabetes: implications for O2supply to skeletal muscle

Erythrocytes release both O(2) and a vasodilator, ATP, when exposed to reduced O(2) tension. We investigated the hypothesis that ATP release is impaired in erythrocytes of humans with type 2 diabetes (DM2) and that this defect compromises the ability of these cells to stimulate dilation of resistance vessels. We also determined whether a general vasodilator, the prostacyclin analog iloprost (ILO), stimulates ATP release from healthy human (HH) and DM2 erythrocytes. Finally, we used a computational model to compare the effect on tissue O(2) levels of increases in blood flow directed to areas of increased O(2) demand (erythrocyte ATP release) with nondirected increases in flow (ILO). HH erythrocytes, but not DM2 cells, released increased amounts of ATP when exposed to reduced O(2) tension (Po(2) < 30 mmHg). In addition, isolated hamster skeletal muscle arterioles dilated in response to similar decreases in extraluminal O(2) when perfused with HH erythrocytes, but not when perfused with DM2 erythrocytes. In contrast, both HH and DM2 erythrocytes released ATP in response to ILO. In the case of DM2 erythrocytes, amounts of ATP released correlated inversely with glycemic control. Modeling revealed that a functional regulatory system that directs blood flow to areas of need (low O(2)-induced ATP release) provides appropriate levels of tissue oxygenation and that this level of the matching of O(2) delivery with demand in skeletal muscle cannot be achieved with a general vasodilator. These results suggest that the inability of erythrocytes to release ATP in response to exposure to low-O(2) tension could contribute to the peripheral vascular disease of DM2.

Effect of Phytic Acid on Suicidal Erythrocyte Death

Phytic acid, an anticarcinogenic food component, stimulates apoptosis of tumor cells. Similar to apoptosis, human erythrocytes may undergo suicidal death or eryptosis, characterized by cell membrane scrambling and cell shrinkage. Triggers of eryptosis include energy depletion. Phytate intake could cause anemia, an effect attributed to iron complexation. The present experiments explored whether phytic acid influences eryptosis. Supernatant hemoglobin concentration was determined to reveal hemolysis, annexin V-binding in FACS analysis was utilized to identify erythrocytes with scrambled cell membrane, forward scatter in FACS analysis was taken as a measure of cell volume, and a luciferin-luciferase assay was employed to determine erythrocyte ATP content. As a result, phytic acid (>or=1 mM) did not lead to significant hemolysis, but significantly increased the percentage of annexin V-binding erythrocytes, significantly decreased forward scatter, and significantly decreased cellular ATP content. In conclusion, phytic acid stimulates suicidal human erythrocyte death, an effect paralleling its proapoptotic effect on nucleated cells.