On the respiratory function of haemoglobin

An investigation of gill and blood carbonic anhydrase characteristics in three basal actinopterygian species: alligator gar (Atractosteus spatula), white sturgeon (Acipenser transmontanus) and Senegal bichir (Polypterus senegalus)

Many teleosts possess a unique set of respiratory characteristics allowing enhanced oxygen unloading to the tissues during stress. This system comprises three major components: highly pH sensitive haemoglobins (large Bohr and Root effects), rapid red blood cell (RBC) intracellular pH (pHi) protection, and a heterogeneous distribution of membrane-bound plasma-accessible carbonic anhydrase (paCA; absence in the gills). The first two components have received considerable research effort; however, the evolutionary loss of branchial paCA has received little attention. In the current study, we investigated the availability of branchial membrane-bound CA, along with several other CA-related characteristics in species belonging to three basal actinopterygian groups: the Lepisosteiformes, Acipenseriformes and Polypteriformes to assess the earlier hypothesis that Root effect haemoglobins constrain branchial paCA availability. We present the first evidence suggesting branchial membrane-bound CA presence in a basal actinopterygian species: the Senegal bichir (Polypterus senegalus) and show that like the teleosts, white sturgeon (Acipenser transmontanus) and alligator gar (Atractosteus spatula) do not possess branchial membrane-bound CA. We discuss the varying respiratory strategies for these species and propose that branchial paCA may have been lost much earlier than previously thought, likely in relation to the changes in haemoglobin buffer capacity associated with the increasing magnitude of the Bohr effect. The findings described here represent an important advancement in our understanding of the evolution of the unique system of enhanced oxygen unloading thought to be present in most teleosts, a group that encompasses half of all vertebrates.

Regulation of erythrocyte function: Multiple evolutionary solutions for respiratory gas transport and its regulation in fish

Gas transport concepts in vertebrates have naturally been formulated based on human blood. However, the first vertebrates were aquatic, and fish and tetrapods diverged hundreds of millions years ago. Water-breathing vertebrates live in an environment with low and variable O₂ levels, making environmental O₂ an important evolutionary selection pressure in fishes, and various features of their gas transport differ from humans. Erythrocyte function in fish is of current interest, because current environmental changes affect gas transport, and because especially zebrafish is used as a model in biomedical studies, making it important to understand the differences in gas transport between fish and mammals to be able to carry out meaningful studies. Of the close to thirty thousand fish species, teleosts are the most species-numerous group. However, two additional radiations are discussed: agnathans and elasmobranchs. The gas transport by elasmobranchs may be closest to the ancestors of tetrapods. The major difference in their haemoglobin (Hb) function to humans is their high urea tolerance. Agnathans differ from other vertebrates by having Hbs, where cooperativity is achieved by monomer-oligomer equilibria. Their erythrocytes also lack the anion exchange pathway with profound effects on CO₂ transport. Teleosts are characterized by highly pH sensitive Hbs, which can fail to become fully O₂ -saturated at low pH. An adrenergically stimulated Na⁺ /H⁺ exchanger has evolved in their erythrocyte membrane, and plasma-accessible carbonic anhydrase can be differentially distributed among their tissues. Together, and differing from other vertebrates, these features can maximize O₂ unloading in muscle while ensuring O₂ loading in gills.

Murine lung tumor response after exposure to cigarette mainstream smoke or its particulate and gas/vapor phase fractions

Knowledge on mechanisms of smoking-induced tumorigenesis and on active smoke constituents may improve the development and evaluation of chemopreventive and therapeutic interventions, early diagnostic markers, and new and potentially reduced-risk tobacco products. A suitable laboratory animal disease model of mainstream cigarette smoke inhalation is needed for this purpose. In order to develop such a model, A/J and Swiss SWR/J mouse strains, with a genetic susceptibility to developing lung adenocarcinoma, were whole-body exposed to diluted cigarette mainstream smoke at 0, 120, and 240 mg total particulate matter per m(3) for 6h per day, 5 days per week. Mainstream smoke is the smoke actively inhaled by the smoker. For etiological reasons, parallel exposures to whole smoke fractions (enriched for particulate or gas/vapor phase) were performed at the higher concentration level. After 5 months of smoke inhalation and an additional 4-month post-inhalation period, both mouse strains responded similarly: no increase in lung tumor multiplicity was seen at the end of the inhalation period; however, there was a concentration-dependent tumorigenic response at the end of the post-inhalation period (up to 2-fold beyond control) in mice exposed to the whole smoke or the particulate phase. Tumors were characterized mainly as pulmonary adenomas. At the end of the inhalation period, epithelial hyperplasia, atrophy, and metaplasia were found in the nasal passages and larynx, and cellular and molecular markers of inflammation were found in the bronchoalveolar lavage fluid. These inflammatory effects were mostly resolved by the end of the post-inhalation period. In summary, these mouse strains responded to mainstream smoke inhalation with enhanced pulmonary adenoma formation. The major tumorigenic potency resided in the particulate phase, which is contrary to the findings published for environmental tobacco smoke surrogate inhalation in these mouse models.

Use of hemoglobin raffimer for postoperative life-threatening anemia in a Jehovah’s Witness

PURPOSE

To describe the successful treatment of acute, life-threatening anemia with the oxygen therapeutic agent, hemoglobin (Hb) raffimer.

CLINICAL FEATURES

A 53-yr-old female Jehovah's Witness developed severe anemia following total hip replacement. Due to prior patient directive, red blood cells were not transfused. Tachycardia, hypotension, electrocardiographic abnormalities and mental status changes developed with a nadir Hb concentration of 3.2 g x dL(-1). Hb raffimer is a purified, cross-linked, human Hb solution developed as a substitute for red blood cell Hb. After obtaining informed consent as well as Food and Drug Administration and Institutional Review Board approval for compassionate use, 2 L of Hb raffimer (Hemolink, Hemosol, Inc., Toronto, ON, Canada) were administered along with ferrous sulfate and epoetin alfa therapy. The patient's Hb level rose to 5.5 g x dL(-1) with resolution of symptoms. To allow recovery of red blood cell mass while maintaining Hb level > 4.5 g x dL(-1), additional 1000 mL doses of Hb raffimer were administered on postoperative days three, five and seven (total dose = 500 g Hb). The patient developed no serious adverse events related to treatment with Hb raffimer. By postoperative day 14, the patient's Hb level increased to 6.5 g x dL(-1) with a hematocrit of 23%. The patient was discharged.

CONCLUSIONS

Use of Hb raffimer as a bridge to recovery of this patient's red blood cell mass may have prevented adverse clinical outcome. Because this product is a purified Hb solution devoid of other cellular components, it may be accepted as therapy by patients who, due to religious conviction, refuse allogeneic red blood cell transfusion.

Haemoglobin function in vertebrates: evolutionary changes in cellular regulation in hypoxia

The evolution of erythrocytic hypoxia responses is reviewed by comparing the cellular control of haemoglobin-oxygen affinity in agnathans, teleost fish and terrestrial vertebrates. The most ancient response to hypoxic conditions appears to be an increase in cell volume, which increases the haemoglobin-oxygen affinity in lampreys. In teleost fish, an increase of cell volume in hypoxic conditions is also evident. The volume increase is coupled to an increase in erythrocyte pH. These changes are caused by an adrenergic activation of sodium/proton exchange across the erythrocyte membrane. The mechanism is important in acute hypoxia and is followed by a decrease in cellular adenosine triphosphate (ATP) and guanosine triphosphate (GTP) concentrations in continued hypoxia. In hypoxic bird embryos, the ATP levels are also reduced. The mechanisms by which hypoxia decreases cellular ATP and GTP concentrations remains unknown, although at least in bird embryos cAMP-dependent mechanisms have been implicated. In mammals, hypoxia responses appear to occur mainly via modulation of cellular organic phosphate concentrations. In moderate hypoxia, 2,3-diphosphoglycerate levels are increased as a result of alkalosis caused by increased ventilation.

Oxygen binding and aggregation of hemoglobin from the common European frog, Rana temporaria

The hemoglobin from the European frog, Rana temporaria, consists of one major and three minor components. The tetramers aggregate upon deoxygenation notably at pH 7:3. Aggregation due to formation of disulphide bridges, as occurs in related species, was observed only in polyacrylamide gels. The hemolysate showed a pronounced Bohr effect. Oxygen affinity decreased with increasing hemoglobin concentration, indicating that aggregation affects the functional properties of the hemolysate. Oxygen binding equilibria of unfractionated hemolysate are insensitive to chloride and show low sensitivity to ATP. Analysis of oxygen equilibrium curves in terms of the two-state allosteric model (MWC) showed that pH change exerted a greater effect on the association constant of the oxygenated state (KR) than that of the deoxy state (KT). The number of interacting binding sites (q) increased with hemoglobin concentration. Cooperativity of oxygen binding, evaluated as Hill coefficient n, never exceeded the value of 3.0. Earlier studies on hemoglobin and blood from this and related species, report significantly higher n values at high O2 saturation. Molecular adaptive aspects are discussed.

The Haldane effect under different acid-base conditions in premature and adult humans

The Haldane effect (HE) was investigated in human adults and prematures under normal metabolic acid-base conditions but at different levels of PCO2. Venous blood samples were equilibrated with low and high PCO2 in either O2 or N2. The change in plasma pH of oxygenated blood by deoxygenation did not differ between both groups. Thus, ontogenetic differences of human hemoglobin structure do not influence the net proton Haldane effect measured in terms of whole blood pH-changes. Since the present data quantitatively agree with those we reported earlier for rabbits, cats and dogs (Kiwull-Schöne et al., 1992), phylogenetic differences in hemoglobin structure of these mammalian species do not either seem to play a role in this respect. The influence of the Haldane effect on plasma pH has to be considered in blood-gas and acid-base analysis of samples with incomplete oxygenation. This is important for the indirect determination of PCO2 through pH by the equilibration method (Astrup and Schrøder, 1956), serving as reference method for determination of metabolic acid-base status and CO2 buffering capacity. Likewise, HE-correction is important for indirect estimation of metabolic acid-base status (BE and HCO-3st) from clinical routine PCO2- and pH-measurement. In spite of the vaste amount of literature on the Haldane effect in human blood, quantitative data for practical purpose are less available and still equivocal. By the present study, a strong inverse linear correlation between the HE-induced delta pH and 1g[HCO3-] could be shown over a wide range of acid-base changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on avian erythrocyte metabolism. XVI. Accumulation of 2,3-bisphosphoglycerate with shifts in oxygen affinity of chicken erythrocytes

The ability of the chicken erythrocyte to accumulate 2,3-bisphosphoglycerate (2,3-P2-glycerate) and its effect upon the oxygen affinity (P50) of the cell suspensions have been determined. Erythrocytes from chick embryos, which contain 4-6 mM 2,3-P2-glycerate, and from chickens at various ages, which contain 3-4 mM inositol pentakisphosphate but no 2,3-P2-glycerate, were incubated with inosine, pyruvate, and inorganic phosphate. Red blood cells from 20-day chick embryos incubated in Krebs-Ringer, pH 7.45, containing 20 mM inosine and 20 mM pyruvate had an increase in 2,3-P2-glycerate from 4.3 to 11.9 mM after 4 h. Importantly, as 2,3-P2-glycerate concentration increased there was a corresponding increase in P50 of the cell suspension. Further, erythrocytes from 9- and 11-week, and 7-, 14-, 24-, and 28-month-old chickens when incubated similarly with inosine and pyruvate accumulated 2,3-P2-glycerate with corresponding increases in P50 of the cell suspensions. The ability of the red cell to accumulate this compound under the incubation conditions used apparently decreases with age of the bird (e.g., 11.9 mM in the 20-day embryo to 1.1 mM in the 28-month-old chicken after 4 h incubation). Despite the presence of significant amounts of inositol-P5, the accumulation of 2,3-P2-glycerate markedly decreases oxygen affinity of the cell suspensions. The delta P50/mumol increase in 2,3-P2-glycerate in the red cells of the 20-day chick embryo after 4 h incubation is 1.5 Torr; conversely, the delta P50/mumol decrease in 2,3-P2-glycerate in the red cells of the 17-day embryo after 6 h incubation in the presence of sodium bisulfite is 2.8 Torr. The demonstrated ability of the chicken erythrocyte to accumulate 2,3-P2-glycerate in response to certain substrates suggests that regulation of concentration of this compound could contribute significantly to regulation of blood oxygen affinity in birds.

The effects of CO2 and fixed acid on the O2-Hb affinity of rabbit and cat blood

The action of respiratory and metabolic acid-base disturbances on the O2-Hb affinity was studied in rabbits and cats. Blood samples of both species were exposed to in vitro pH-changes, which were either achieved by variation of PCO2 (2.8-8.3 kPa) at constant lactic acid concentration, or by addition of lactic acid (5-14 mmol X 1(-1) at constant PCO2. The PO2 at halfsaturation (P50) and the Hill's n were determined from O2-Hb dissociation curves (ODC) in a range between 20 and 80% SO2. Under standard conditions (T = 311 K, PCO2 = 5.33 kPa, pH = 7.4), the average P50 value was 4.66 +/- 0.05 kPa in rabbits, that is slightly higher than reported by others, and 5.17 +/- 0.03 kPa in cats. The average values of Hill's n were 2.91 +/- 0.02 and 2.95 +/- 0.03 for rabbits and cats, respectively. When plasma pH was varied by CO2, the resulting classical CO2 Bohr factor phi CO2 = delta lgP50/delta pH50 was distinctly higher in cats (-0.560 +/- 0.006, n = 25) than in rabbits (-0.504 +/- 0.014, n = 22), although in the latter species being even higher than reported elsewhere. Concomitant metabolic acidosis did not significantly affect phi CO2, but shifted the P50 at a given plasma pH to lower values. Substitution of lactic acid with equimolar amounts of sodium lactate left both phi CO2 and P50 unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Bohr effect, electron spin resonance spectroscopy and subunit dissociation of the hemoglobin components from the turtle Phrynops hilarii

Isoelectric points of the two haemoglobin components from the fresh-water turtle, Phrynops hilarii, were estimated by isoelectric focusing electrophoresis (IEF) to be 7.6 and 6.3, respectively for component I (CI) and component II (CII). For further studies, CI and CII were isolated by ion exchange chromatography. At pH 7.1, the estimated intraerythrocytic pH, at 25 degrees C, the values of P50, for the stripped haemoglobins, are: 19 torr for CI; 40 torr for CII and 28 torr for the whole haemolysate (pht). Oxygen binding with the stripped isolated components (CI and CII) and with the whole haemolysate (pht) show that delta log P50/delta pH, in the pH interval from 6.8 to 8.5, to be: CI = -0.35; CII = -0.80 and pht = -0.47. The Bohr curves for CI and CII intercept at pH 7.8. eta 50 for CI was 3 and invariant with pH. CII, at the more acid pH range showed biphasic Hill plots. pht shows a eta 50 that varies with pH. CI is affected by ATP, ADP, GTP and slightly by CO2, whereas CII is totally insensitive to CO2 and ATP. Additionally both components are not affected by inositol phosphates. Electron spin resonance (ESR) spectra of both components at pH 8.4 and 6.4 show that CI fails to undergo a R----T transition, while CII, with the higher Bohr effect, undergoes the R----T transition driven by pH. Molecular sieving studies of the liquid nitrogen stored CI, CII and pht show them to be disulphide polymers, CI with an apparent mol. wt of 150 X 10(3) and CII and pht of 100 X 10(3).(ABSTRACT TRUNCATED AT 250 WORDS)

On the seemingly diminished CO2-Bohr effect in hypoxic chemodenervated rabbits

In hypoxic rabbits, different levels of Pco2 before and after carotid chemodenervation were applied in order to get information about the acid-base status and the position of the O2-Hb dissociation curve (ODC). A CO2-induced change in pH caused a smaller change in the half-saturation pressure (P50) than was to be expected from the CO2-Bohr effect alone. Considering both, the numerically different CO2- and fixed acid-Bohr factors as well as the corresponding respiratory or metabolic pH changes, a method is presented to calculate the position of the ODC with high accuracy. From these considerations it can be derived that the seemingly diminished CO2-Bohr effect in hypoxic rabbits in vivo, especially after chemodenervation , is due more or less to accumulation of lactid acid. This leads to an increasing error if only the CO2-Bohr factor and the actual pH change are taken into account.

Fetal oxygen affinity and its parameters in a random obstetric population

Fetal oxygenation studies have provided the obstetrician with some basic information regarding oxygen supply to the fetus. Although standard values for normal fetuses at term have been made, little has been done to evaluate any changes occurring with fetal and neonatal abnormality. Twenty-two sets of analyses were performed to measure oxygen affinity (P50) 2,3-diphosphoglycerate concentration and full blood gas analysis on umbilical arterial and venous samples. The samples were taken from a random obstetric population. All babies were at term or post term by antenatal data and paediatric assessment at delivery. A further study was performed on a group of normal and growth retarded term infants, assessing the same parameters as the random population. Following analysis, 2 cases of cardio-pulmonary abnormality, resulting in neonatal death, were found to have the highest oxygen affinity, the remaining oxygenation parameters of PO2, PCO2, pH and 2,3-diphosphoglycerate concentration were found to be similar to the rest of the group. The results of this study agree with previous investigative findings for the normal babies. The finding of low P50 (or high oxygen affinity) in these 2 cases is an unusual finding and may reflect an adaptive function towards extra-uterine life. No alteration of fetal oxygen affinity was found in a small group of growth retarded babies despite the lowering of the 2,3-diphosphoglycerate concentration. The latter finding probably reflects the lowered intrauterine fetal blood pH found with growth retarded babies. Further research is required to elucidate the comples process of fetal oxygenation that occurs in the presence of fetal abnormality.

An O2-Hb "paradox' in frog blood? (n-values exceeding 4.0)

O2-Hb dissociation curves have been determined for the anurans, Rana temporaria and Rana catesbeiana, and compared with human blood for the specific purpose of defining the n-value (hill's cooperativity coefficient) at high O2 saturations. The P50 values at normal conditions (see fig. 1) for each species were 24.6 mm Hg for human blood, 37.0 mm Hg for Rana temporaria blood and 53.5 mm Hg for Rana catesbeiana. For human blood the n-value was 2.7 at saturations from 36% to 98% levelling off at the highest saturations. For Rana temporaria Hill plots between saturations from 20% to 98% showed 3 segments. The average n-value increased from 1.6 to 2.4 at about 50% saturation, increasing again at about 80% saturation to 7.3. The pattern in Rana catesbeiana blood was similar with the n-value changing from 1.6 to 3.1 at about 50% saturation, averaging 3.5 between 53% and 89% saturation. Additionally the Bohr effect in Rana temporaria blood more than doubled when compared at 50% and 90% saturation. The data show that for R. temporaria blood the free energy of interaction associated with the binding of 02 to Hb is displaced to the upper segment of the dissociation curve.

Bohr effect induced by CO2 and fixed acid at various levels of O2 saturation in duck blood

The Bohr factor, phi = delta log Po2/deltapH, was determined at various levels of hemoglobin O2 saturation (SO2) in fresh whole blood of the duck. Plasma pH was varied by either changing PCO2 of the blood at constant base excess (CO2 Bohr factor, phiCO2) or by addition of NaHCO3 and HCl at constant PCO2 (fixed acid BOHR factor, phiAH). No differences were found between phiCO2 and phiAH at SO2 levels between 20 and 85%, and there was no saturation dependence of the Bohr factor, its average value being -0.44. It is concluded that in whole blood of this bird species CO2 exerts no direct effect on the O2 affinity of hemoglobin.

The oxygen affinity of chicken haemoglobin in whole blood and erythrocyte suspensions

The oxygen equilibrium of whole chicken blood has a P50 of 52.3 mm Hg and a Hill coefficient of 2.6 at pH 7.4 and 37 degrees C when determined with new microtechniques which are not vitiated by cellular respiration. The apparent failure of the haemoglobin to reach full saturation at arterial PO2 IS DISCUSSED IN RELATION TO THE HAEMoglobin-oxygen equilibrium concept. The low affinity observed is due to intraerythrocytic inositol pentaphosphate (IPP), and the affinity of a haemolysate "stripped" of IPP is greatly increased (deltalog P50 =1.25). Unlike the mamalian analogue 2, 3-diphosphoglycerate, IPP concentration of whole blood does not decrease after incubation for 10 hr at 37 degreesC.

Influence of 2,3-diphosphoglycerate on the buffering properties of human blood: role of the red cell membrane

The effect of the concentration of red cell 2,3-diphosphoglycerate (2,3-DPG, 0.5-21 mumoles/g cells) on the buffering properties and on the slope of the relation between the extracellular and intracellular pH (deltapHi/deltapHe) of human blood was studied. The results were evaluated in connection with previous findings concerning the effect of 2,3-DPG on the Donnan ratio rH+ = H+e/H+i. deltapHi/deltapHe decreases with rising red cell 2,3-DPG content as well as with rising extracellular pH. deltapHi/deltapHe and rH+ can be related to each other by the empirical equation deltapHi/deltapHe = 1 + log rH+ = 1 + pHi - pHe. The validity of this equation appears to be restricted to conditions where the Donnan ratio rH+ is altered between 0.3 and 1 either by changes of the red cell concentration of buffering anions such as 2,3-DPG or by changes of the extracellular pH. As determined in suspensions of red cells with intact membranes, the 2,3-DPG-and pH-induced changes of deltapHi/deltapHe lead to proportional changes in the buffering power of the non-bicarbonate buffers of erythrocytes. Due to this effect the buffering power of suspensions of cells containing 5 times the normal concentration of the buffer 2,3-DPG is lower than that of cells with normal 2,3-DPG content (at extracellular pH values above 7). These findings demonstrate that the action of intracellular non-bicarbonate buffers in blood is effectively modulated by the physico-chemical properties of the red cell membrane.