Effects of sulfhydryl reagents on the anti-sickling activity of some membrane-interacting compounds

Under deoxygenated conditions (PO2 = 0 mmHg), sulfhydryl reagents such as N-ethylmaleimide and iodoacetamide had no effect on sickling, but they did inhibit the anti-sickling activity of chlorpromazine. At the same concentration, these sulfhydryl reagents inhibited the cup formation of chlorpromazine in an oxygenated state (PO2 = 143 mmHg). This supports our previous finding that the anti-sickling effect of membrane-interacting compounds is related to their ability to form a cup-shaped red cell.     

Predict fetal brain PO2 during hypoxaemia and anemia in sheep

The mean brain PO2 of fetal sheep was calculated using equations based on the Krogh cylinder model of O2 diffusion. This analysis took into account the effect of red cell spacing on capillary PO2. Uncompensated changes in arterial O2 tension, the radius of the Krogh cylinder, and metabolic rate of brain tissue were predicted to affect mean brain PO2 more than uncompensated changes in brain blood flow or haemoglobin concentration. Under normal conditions (CaO2 = 7.42 ml/dl), the mean PO2 of the fetal brain was calculated to be about 12 mmHg. Hypoxaemia decreased the predicted mean O2 tension to 7.6 mmHg (CaO2 = 5.19 ml/dl), 5.0 mmHg (CaO2 = 4.11 ml/dl), and 4.3 ml/dl (CaO2 = 3.50 ml/dl). Isovolaemic anaemia reduced mean brain PO2 to 8.7 mmHg (CaO2 = 4.40 ml/dl), 8.3 mmHg (CaO2 = 3.94 ml/dl), and 7.3 mmHg (CaO2 = 3.19 ml/dl). During anaemia the increased distance between red cells was calculated to contribute significantly to brain hypoxaemia. A summary equation is presented which enables the investigator to estimate easily the mean PO2 of the fetal brain when several factors are changed from standard values.     

Oxygen transport in the rat brain cortex at normobaric hyperoxia

The distribution of oxygen tension (PO(2)) in microvessels and in the tissues of the rat brain cortex on inhaling air (normoxia) and pure oxygen at atmospheric pressure (normobaric hyperoxia) was studied with the aid of oxygen microelectrodes (diameter = 3-6 microm), under visual control using a contact optic system. At normoxia, the PO(2) of arterial blood was shown to decrease from [mean (SE)] 84.1 (1.3) mmHg in the aorta to about 60.9 (3.3) mmHg in the smallest arterioles, due to the permeability of the arteriole walls to oxygen. At normobaric hyperoxia, the PO(2) of the arterial blood decreased from 345 (6) mmHg in the aorta to 154 (11) mmHg in the smallest arterioles. In the blood of the smallest venules at normoxia and at normobaric hyperoxia, the differences between PO(2) values were smoothed out. Considerable differences between PO(2) values at normoxia and at normobaric hyperoxia were found in tissues at a distance of 10-50 microm from the arteriole walls (diameter = 10-30 microm). At hyperbaric hyperoxia these values were greater than at normoxia, by 100-150 mmHg. In the long-run, thorough measurements of PO(2) in the blood of the brain microvessels and in the tissues near to the microvessels allowed the elucidation of quantitative changes in the process of oxygen transport from the blood to the tissues after changing over from the inhalation of air to inhaling oxygen. The physiological, and possibly pathological significance of these changes requires further analysis.     

Prevention of in vitro sickling of human erythrocytes by monofunctional amidination

Treatment of sickle erythrocytes with the monoimidate, ethylacetimidate, prevented anoxia-induced sickling in vitro. Hemoglobin isolated from amidated erythrocytes exhibited an increase in the minimum gelling concentration compared to untreated preparations. Although the prevention of sickling did appear to involve chemical modification of hemoglobin S, an increase in the oxygen affinity was not a requisite for the antisickling activity of the imidates. Our results suggest that substitution of amidino for amino groups prevents the aggregation of deoxyhemoglobin S. Furthermore, comparison of monoimidates with bifunctional reagents indicates that molecular crosslinking is not essential for antisickling activity.     

Oxygen distribution and consumption in the cat retina during normoxia and hypoxemia

Oxygen tension (PO2) was measured with microelectrodes within the retina of anesthetized cats during normoxia and hypoxemia (i.e., systemic hypoxia), and photoreceptor oxygen consumption was determined by fitting PO2 measurements to a model of steady-state oxygen diffusion and consumption. Choroidal PO2 fell linearly during hypoxemia, about 0.64 mmHg/mmHg decrease in arterial PO2 (PaO2). The choroidal circulation provided approximately 91% of the photoreceptors' oxygen supply under dark-adapted conditions during both normoxia and hypoxemia. In light adaptation the choroid supplied all of the oxygen during normoxia, but at PaO2's less than 60 mmHg the retinal circulation supplied approximately 10% of the oxygen. In the dark-adapted retina the decrease in choroidal PO2 caused a large decrease in photoreceptor oxygen consumption, from approximately 5.1 ml O2/100 g.min during normoxia to 2.6 ml O2/100 g.min at a PaO2 of 50 mmHg. When the retina was adapted to a rod saturating background, normoxic oxygen consumption was approximately 33% of the dark-adapted value, and hypoxemia caused almost no change in oxygen consumption. This difference in metabolic effects of hypoxemia in light and dark explains why the standing potential of the eye and retinal extracellular potassium concentration were previously found to be more affected by hypoxemia in darkness. Frequency histograms of intraretinal PO2 were used to characterize the oxygenation of the vascularized inner half of the retina, where the oxygen distribution is heterogeneous and simple diffusion models cannot be used. Inner retinal PO2 during normoxia was relatively low: 18 +/- 12 mmHg (mean and SD; n = 8,328 values from 36 profiles) in dark adaptation, and significantly lower, 13 +/- 6 mmHg (n = 4,349 values from 19 profiles) in light adaptation. Even in the dark-adapted retina, 30% of the values were less than 10 mmHg. The mean PO2 in the inner (i.e., proximal) half of the retina was well regulated during hypoxemia. In dark adaptation it was significantly reduced only at PaO2's less than 45 mmHg, and it was reduced less at these PaO2's in light adaptation.     

Hypoxia reduces oxygen consumption of fetal skeletal muscle cells in monolayer culture.

In a previous study on acute asphyxia in unanesthetized fetal sheep near term we showed that reduced oxygen delivery to peripheral organs reduces total oxygen consumption, suggesting that oxygen itself may be a determinant of oxygen consumption (Jensen, Hohmann & Künzel, 1987). To test this hypothesis we developed an in vitro perfusion model, which enabled us to measure the oxygen consumption of fetal skeletal muscle cells in monolayer culture in a control period (at approximately 145 mmHg) and during various degrees of hypoxia (6-140 mmHg). In 57 experiments on 57 cultures the mean oxygen consumption at a mean 'entry PO2' of 145.3 +/- 10.4 mmHg was 10.3 +/- 9.3 (SD).10(-6) microliters O2 per h per skeletal muscle cell. These measurements were made after an average of 4.2 +/- 2.3 transfers of the cells and at a cell density of 2.0 +/- 1.2.10(5) cells per cm2. In 54 of these experiments hypoxia was induced. There was a close positive correlation between the PO2 of the perfusate entering the Petridish ('entry PO2') and the change of the oxygen consumption of the cells (y = 5.17 - 0.54x + 0.03x2 - 0.00016x3, r = 0.97, p less than 0.0001). When oxygen tension fell, there was a concomitant fall in cellular oxygen consumption. We conclude that oxygen is a determinant of cellular oxygen consumption. Thus, hypoxia may reduce oxygen consumption of skeletal muscle cells, and oxygen may be preserved to maintain oxidative metabolism in central fetal organs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of phenylalanine- or tryptophan-loaded liposomes on the rheological properties of AA and SS erythrocytes

Phenylalanine or tryptophan was incorporated into AA and SS red blood cells by a liposomal transport system which was previously shown by Kumpati to inhibit and reverse sickling of intact SS red blood cells in vitro. In the present study, the effect of phenylalanine or tryptophan incorporation on the rheological properties was evaluated. The incorporation of phenylalanine or tryptophan into red blood cells decreased the viscosity of deoxy SS red blood cells which reached a level close to that for normal red blood cells due to the antisickling effect. These results demonstrate that this liposomal transport system which transferred phenylalanine or tryptophan into intact red cells and did not have any adverse effect on red cell metabolism or function did correct the viscosity of deoxy SS red cells by its antisickling effect. This method may have significant therapeutic implications in the treatment of sickle cell disease.     

Comparison of tumor and normal tissue oxygen tension measurements using OxyLite or microelectrodes in rodents

In this study we compare oxygen tension (PO2) histograms measured with O2 microelectrodes and a new optical PO2 measurement device, the OxyLite, in normal tissues (mouse spleen and thymus) and in tumors (R3230Ac in rats) (n = 5-6). The transient response to glucose infusion or 100% O2 breathing (hyperoxia) was also measured in tumors. PO2 histograms of spleen and thymus with the two devices were not different. The OxyLite tumor PO2 histogram, however, was left-shifted compared with the microelectrode (median PO2 1.0 vs. 4.0 mmHg, P = 0.016). Both probes responded to acute hyperglycemia with a mean increase of 3-6 mmHg, but the microelectrode change was not significant. The OxyLite consistently recorded large PO2 increases (approximately 28 mmHg) with hyperoxia, whereas the microelectrode response was variable. The OxyLite averages PO2 over an area that contains interstitial and vascular components, whereas the microelectrode measures a more local PO2. This study demonstrates the importance of considering the features of the measurement device when studying tissues with heterogeneous PO2 distributions (e.g., tumors).     

Effect of intracellular magnesium and oxygen tension on K+-Cl- cotransport in normal and sickle human red cells.

In red cells from normal individuals (HbA cells), the K+-Cl- cotransporter (KCC) is inactivated by low O2 tension whilst in those from sickle cell patients (HbS cells), it remains fully active. Changes in free intracellular [Mg2+] have been proposed as a mechanism. In HbA cells, KCC activity was stimulated by Mg2+ depletion and inhibited by Mg2+ loading but the effect of O2 was independent of Mg2+. At all [Mg2+]is, the transporter was stimulated in oxygenated cells, minimally active in deoxygenated ones. By contrast, the stimulatory effects of O2 was abolished by inhibitors of protein (de)phosphorylation. HbS cells had elevated KCC activity, which was of similar magnitude in oxygenated and deoxygenated cells, regardless of Mg2+ clamping. In deoxygenated cells, the antisickling agent dimethyl adipimidate inhibited sickling, Psickle and KCC. Results indicate a role for protein phosphorylation in O2 dependence of KCC, with different activities of the relevant enzymes in HbA and HbS cells, probably dependent on Hb.     

Changes in heart rate during progressive hyperoxia in the dogfish Scyliorhinus canicula L.: evidence for a venous oxygen receptor

Progressive hyperoxia caused a gradual increase in arterial blood oxygen tension (PaO2). Initially there was no change in venous O2 tension (PvO2) but in extreme hyperoxia (PO2 650 mmHg) it increased to 2.5 times the normoxic (PO2 150 mmHg) level (Table 1). Ventilation frequency gradually decreased down to 73% of the normoxic value as PO2 rose towards a maximum at 700 mmHg (Fig. 1). In moderately hyperoxic water (mean PO2 233 mmHg) heart rate (fH) increased significantly above the normoxic level. Further increases in ambient PO2 caused a progressive reduction in fH to a level significantly below the normoxic rate in extreme hyperoxia (Fig. 2). Injection of atropine abolished these changes, and the atropinized fH was similar to that measured during moderate hyperoxia. The initial increase in fH during progressive hyperoxia is attributed to release of vagal tone, due to removal of normoxic stimulation of peripheral oxygen receptors; whereas, the secondary bradycardia is attributed to the stimulation of oxygen receptors located in the venous system. Injection of 5 ml of hyperoxaemic blood into the venous system of normoxic fish caused a transient bradycardia (Fig. 3), lasting a mean of 73 sec, which is the approximate time for passage of the blood volume of the venous system through the heart. This bradycardia was neither pH dependent nor a pressor response and provides supporting evidence for the existence of a venous oxygen receptor.     

Potassium channel types in arterial chemoreceptor cells and their selective modulation by oxygen.

Single K+ channel currents were recorded in excised membrane patches from dispersed chemoreceptor cells of the rabbit carotid body under conditions that abolish current flow through Na+ and Ca2+ channels. We have found three classes of voltage-gated K+ channels that differ in their single-channel conductance (gamma), dependence on internal Ca2+ (Ca2+i), and sensitivity to changes in O2 tension (PO2). Ca(2+)-activated K+ channels (KCa channels) with gamma approximately 210 pS in symmetrical K+ solutions were observed when [Ca2+]i was greater than 0.1 microM. Small conductance channels with gamma = 16 pS were not affected by [Ca2+]i and they exhibited slow activation and inactivation time courses. In these two channel types open probability (P(open)) was unaffected when exposed to normoxic (PO2 = 140 mmHg) or hypoxic (PO2 approximately 5-10 mmHg) external solutions. A third channel type (referred to as KO2 channel), having an intermediate gamma(approximately 40 pS), was the most frequently recorded. KO2 channels are steeply voltage dependent and not affected by [Ca2+]i, they inactivate almost completely in less than 500 ms, and their P(open) reversibly decreases upon exposure to low PO2. The effect of low PO2 is voltage dependent, being more pronounced at moderately depolarized voltages. At 0 mV, for example, P(open) diminishes to approximately 40% of the control value. The time course of ensemble current averages of KO2 channels is remarkably similar to that of the O2-sensitive K+ current. In addition, ensemble average and macroscopic K+ currents are affected similarly by low PO2. These observations strongly suggest that KO2 channels are the main contributors to the macroscopic K+ current of glomus cells. The reversible inhibition of KO2 channel activity by low PO2 does not desensitize and is not related to the presence of F-, ATP, and GTP-gamma-S at the internal face of the membrane. These results indicate that KO2 channels confer upon glomus cells their unique chemoreceptor properties and that the O2-K+ channel interaction occurs either directly or through an O2 sensor intrinsic to the plasma membrane closely associated with the channel molecule.     

Enhanced cloning efficiency of mouse bone marrow macrophage progenitors correlates with increased content of CSF-1 receptor of their progeny at low oxygen tension

Mononuclear phagocytes are located in every tissue of metazoan organisms. In this extravascular space, they are designated as macrophages and are known to sense and process many signals including the local oxygen tension (PO2), which ranges from 150 mmHg at the lung apices to around 40 mmHg in mixed venous blood and most organs, and to less than 10 mmHg in tissues where long-term and dynamic remodeling processes occur. Most tissue macrophages survive and maintain their differentiated status within an environment bathed by colony-stimulating factor (CSF)-1 through the CSF-1 receptor, encoded by the Csf1r gene. In order to investigate the mRNA expression profile of macrophages as a function of PO2, we developed an in vitro model in which monocyte-derived macrophages were generated from mouse bone marrow progenitor cells grown and maintained under low (36 mmHg) or atmospheric (142 mmHg) PO2, in the presence of L929-conditioned medium (L-CM) as a source of CSF-1. We show that CSF-1-reactive C57BL/6 bone marrow cells displayed an increased cloning efficiency under a PO2 of 36, compared with 142 mmHg. Furthermore, we provide evidence of the overexpression of both CSF-1 receptor protein and mRNA by mouse monocyte-derived macrophages generated from bone marrow under low PO2.     

Local regulation of pulmonary blood flow and ventilation-perfusion ratios in the coatimundi.

Small catheters (ca. 3 mm diam at tip) were wedged in subsegmental bronchi in anesthetized coatimundi (Nasua nasua) during spontaneous breathing. Mixed expired gases of a group of lobules were sampled continuously without contamination from neighboring units, and local tidal volume, frequency, carbon dioxide production, and oxygen consumption were measured, as well as mixed venous PO2 and PCO2. Local ventilation-perfusion ratio, alveolar PO2, PCO2, and blood flow were calculated. There was a 22% reduction (range 15-38) in local perfusion (as percent of flow at PAO2 100 mmHg) per 10 mmHg fall in local alveolar oxygen tension over the PAO2 range 150-36 mmHg. Local hypercapnia had little effect on local flow. Local tidal volume (ca. 1% of total tidal volume) was unaffected by changes in alveolar gas tensions. The contribution of vasoconstriction or vasodilatation, as a negative feedback system, to the stability of local PAO2 was greatest close to the physiologic range (65-85 mmHg) falloderate efficiency.     

NO synthesis, unlike respiration, influences intracellular oxygen tension.

We have developed a new phosphorescent probe, PdTCPPNa(4), whose luminescence properties are affected by local variations of intracellular oxygen tension (PO(2)). Spectrofluorometric measurements on living human umbilical venous endothelial cells loaded with this molecule show that a decrease in extracellular oxygen tension induces a decrease of PO(2), illustrating the phenomenon of oxygen diffusion and validating the use of this probe in living cells. Moreover, KCN- or 2,4-dinitrophenol-induced modifications of respiration do not lead to detectable PO(2) variations, probably because O(2) diffusion is sufficient to allow oxygen supply. On the contrary, activation by acetylcholine or endothelial nitric oxide synthase (eNOS), which produces NO while consuming oxygen, induces a significant decrease in PO(2), whose amplitude is dependent on the acetylcholine dose, i.e., the eNOS activity level. Hence, activated cytosolic enzymes could consume high levels of oxygen which cannot be supplied by diffusion, leading to PO(2) decrease. Other cell physiology mechanisms leading to PO(2) variations can now be studied in living cells with this probe.     

Covalent binding of glutathione to hemoglobin. I. Inhibition of hemoglobin S polymerization

Thiol reagents react with cysteine beta 93 of hemoglobin and as a result increase the oxygen affinity of hemoglobin. In the present studies we have used a thiol-disulfide exchange between mixed disulfides of hemoglobin and reduced glutathione to attach intracellular glutathione to hemoglobin and to study its antisickling properties. The rates of production of glutathionyl hemoglobin (G-Hb) depend on the structure of the thiol reagent linked to cysteine beta 93. Up to 25% G-Hb can be produced in normal and sickle red cells because of the high intracellular concentration of reduced glutathione. This high level of G-Hb in normal cells increases the oxygen affinity by about 35% and reduces heme-heme interactions. In sickle cells the increased oxygen affinity is associated with an inhibition of sickling of about 70% at 21 mm Hg. Inhibition of polymerization of deoxy HbS is also due to a direct inhibition of intermolecular contacts in the fibers as demonstrated by the increased solubility and the increased delay time of G-HbS compared to deoxy HbS.     

High dose Erythropoietin increases brain tissue oxygen tension in Severe Vasospasm after Subarachnoid Hemorrhage

ABSTRACT: BACKGROUND: Vasospasm-related delayed cerebral ischemia (DCI) significantly impacts on outcome after aneurysmal subarachnoid hemorrhage (SAH). Erythropoietin (EPO) may reduce the severity of cerebral vasospasm and improve outcome, however, underlying mechanisms are incompletely understood. In this study, the authors aimed to investigate the effect of EPO on cerebral metabolism and brain tissue oxygen tension (PbtO2). METHODS: Seven consecutive poor grade SAH patients with multimodal neuromonitoring (MM) received systemic EPO therapy (30.000 IU per day for 3 consecutive days) for severe cerebral vasospasm. Cerebral perfusion pressure (CPP), mean arterial blood pressure (MAP), intracranial pressure (ICP), PbtO2 and brain metabolic changes were analyzed during the next 24 hours after each dose given. Statistical analysis was performed with a mixed effects model. RESULTS: A total of 22 interventions were analyzed. Median age was 47 years (32-68) and 86% were female. Three patients (38%) developed DCI. MAP slightly decreased 2 hours after intervention (P<0.04) without significantly affecting CPP and ICP. PbtO2 significantly increased over time (P<0.05) to a maximum of 7+/-4mmHg increase 16 hours after infusion. Brain metabolic parameters did not change over time. CONCLUSIONS: EPO increases PbtO2 in poor grade SAH patients with severe cerebral vasospasm. The effect on outcome needs further investigation.     

Nitric oxide and endothelin in oxygen-dependent regulation of vascular tone of human umbilical vein

We investigated the possible contribution of nitric oxide (NO) and endothelin (ET) to oxygen-dependent regulation of human umbilical vein vascular tone by simultaneous registration of intracellular membrane potential and isometric tension of vessel strips with and without NO synthase inhibition [10-4 M N omega-nitro-L-arginine methyl ester (L-NAME)], ETA receptor blockade (10(-5) M BQ-123), or ETB receptor blockade (10(-7) M BQ-788) at Po2 values in the bath solution between 5 and 104 mmHg. Increasing PO2 above the physiological intrauterine range resulted in depolarization and an increase of isometric tension, whereas lowering PO2 resulted in hyperpolarization and a decrease in isometric tension. Removal of the endothelium reversed these effects. At PO2 values below 39 mmHg, intact preparations treated with either L-NAME, BQ-788, or BQ-123 were more depolarized than controls. In the case of treatment with L-NAME or BQ-123, this was accompanied by an increase in isometric tension. We conclude that it is NO that mediates the hypoxic hyperpolarization and vasodilatation of the human umbilical vein and that ET, via activation of ETB1 receptors on endothelial cells, contributes to this effect.     

Mitochondrial respiratory control can compensate for intracellular O(2) gradients in cardiomyocytes at low PO(2)

In isolated single cardiomyocytes with moderately elevated mitochondrial respiration, direct evidence for intracellular radial gradients of oxygen concentration was obtained by subcellular spectrophotometry of myoglobin (Mb). When oxygen consumption was increased by carbonyl cyanide m-chlorophenylhydrazone (CCCP) during superfusion of cells with 4% oxygen, PO(2) at the cell core dropped to 2.3 mmHg, whereas Mb near the plasma membrane was almost fully saturated with oxygen. Subcellular NADH fluorometry demonstrated corresponding intracellular heterogeneities of NADH, indicating suppression of mitochondrial oxidative metabolism due to relatively slow intracellular oxygen diffusion. When oxygen consumption was increased by electrical pacing in 2% oxygen, radial oxygen gradients of similar magnitude were demonstrated (cell core PO(2) = 2.6 mmHg). However, an increase in NADH fluorescence at the cell core was not detected. Because CCCP abolished mitochondrial respiratory control while it was intact in electrically paced cardiomyocytes, we conclude that mitochondria with intact respiratory control can sustain electron transfer with reduced oxygen supply. Thus mitochondrial intrinsic regulation can compensate for relatively slow oxygen diffusion within cardiomyocytes.