A mathematical model for gas exchange in the fish gill based on non-linear blood gas equilibrium curves

A mathematical model for gas exchange in fish gills is presented, which makes allowance for the non-linear nature of the oxygen and carbon dioxide equilibrium curves of blood, for the uneven distribution of diffusion conductance along the secondary lamellae, and for coupling of oxygen and carbon dioxide exchange through the Bohr and Haldane effects. The model demonstrates that for oxygen loading in the gill the sigmoid equilibrium curve is superior to a linear one, whereas the non-linearity of the carbon dioxide equilibrium curve does not significantly affect carbon dioxide exchange and that the Bohr and Haldane effects have importance only for carbon dioxide exchange. It is also shown that the arterial and expired gas tensions and concentrations are unaffected by whether the bulk of the diffusion conductance is at either the afferent or the efferent end of the individual lamellae, provided that the total conductance is unchanged.

The primary structure of the hemoglobin of the dogfish shark (Squalus acanthias). Antagonistic effects of ATP and urea on oxygen affinity of an elasmobranch hemoglobin

The amino-acid sequence of the hemoglobin of the Dogfish Shark (Squalus acanthias) is presented. The alpha-chains consist of 141 residues and show a Thr/Ser ambiguity at position 3. The beta-chains consist of 142 residues and evidently have no D-helix; they show an Asn/Tyr ambiguity at position 104. Both chains have free N-terminal amino acids. The phylogenetic distance from the human alpha- and beta-chains is indicated by 49.3% and 56.2% amino-acid exchanges. The primary structure is discussed in relation to the oxygen-binding properties of elasmobranch hemoglobin, particularly as regards the antagonistic effects of urea and ATP, and the effects of proton concentration (the alkaline and acid Bohr effects, and the Root effect).

Functional multiplicity and structural correlations in the hemoglobin system of larvae of Chironomus thummi thummi (Insecta, Diptera): Hb components CTT I, CTT II beta, CTT III, CTT IV, CTT VI, CTT VIIB, CTT IX and CTT X

Larvae of the dipteran insect Chironomus thummi thummi that burrow in fresh-water muds, contain at least 12 hemoglobin (Hb) components of which the functional properties have not been systematically documented, although their amino acid sequences have been elucidated, showing mutually distinct primary structures. We isolated eight components (the monomeric Hbs CTT I, CTT III and CTT IV and the dimeric Hbs CTT II beta, CTT VI, CTT VIIB, CTT IX and CTT X) and measured in each O2 affinity and cooperativity and their pH dependence, and the effects of temperature, NaCl and ATP. The O2 affinities, Bohr- and temperature effects of the isohemoglobins are discussed in relation to mode of life and the microenvironmental conditions to which the larvae are subjected in nature, and with regard to the molecular mechanisms underlying the Hb-oxygenation reactions.

Fixed acid and carbon dioxide Bohr effects as functions of hemoglobin-oxygen saturation and erythrocyte pH in the blood of the frog, Rana temporaria

Using a thin film, dynamic recording technique, the pH sensitivity of the oxygen equilibrium (Bohr effect) of whole blood in the frog Rana temporaria, and its dependence on CO2 and fixed acids and on plasma and erythrocyte pH values were measured. Under standard conditions (20 degrees C, PCO2 = 14.7 mm Hg, pH = 7.65) the oxygen equilibrium could be described by a P50 value of 38 mm Hg and n50 of 1.8 Hill plots of the oxygen equilibria showed increased cooperativity in oxygen binding with increasing saturation (n20 congruent to 1.2, n80 congruent to 4.0). Values of fixed acid and CO2 Bohr factors (phi AH and phi CO2, respectively) were similar at specific saturations (S20, 50, 80) but showed saturation dependence with high values occurring at high saturation. The same statements also hold for the intracellular Bohr factors (derived from the relation between blood P50 and erythrocyte pH) although the values of both phi AH and phi CO2 now were greater than those related to blood pH.

TMAO (trimethylamine oxide)-independence of oxygen affinity and its urea and ATP sensitivities in an elasmobranch hemoglobin

Urea and trimethylamine oxide (TMAO), the major osmolytes in the body fluids of marine elasmobranch fishes, are known to exert counteracting effects on the functions of a variety of enzymes and other proteins of vertebrates (cf. Yancey et al., '82). Although urea raises the O2 affinity of the hemoglobin (Hb) of Squalus acanthias and reduces its sensitivity to the major allosteric cofactor, ATP, the oxygenation reactions of the Hb are insensitive to TMAO, reflecting the absence of urea-TMAO counteraction in the absence or in the presence of the phosphate.

Antagonistic effect of urea on oxygenation-linked binding of ATP in an elasmobranch hemoglobin

The O2 affinity of "stripped" (cofactor-free) hemoglobin (Hb) of the elasmobranch, Squalus acanthias is decreased by ATP, the main erythrocytic phosphate cofactor but increased by urea at physiological concentration. When both compounds are present, as in life, urea decreases the ATP sensitivity, indicating that previous Hb oxygenation studies in the absence of urea overestimate the modulator role of phosphate cofactors in sharks. Whereas ATP decreases the O2 association equilibrium constant of the deoxygenated pigment, urea raises those of both the deoxy and the oxygenated states. Possible mechanisms for the urea-protein interactions i.e. binding at carboxy-termini or carbamylation of amino-termini of the protein chains, are discussed.

Allosteric interactions governing oxygen equilibria in the haemoglobin system of the spiny dogfish, Squalus acanthias

The oxygenation-linked, allosteric interactions of erythrocytic organic phosphates and urea with the haemoglobin (Hb), and the functional significance of the Hb multiplicity, were studies in an elasmobranch, Squalus acanthias. The autochthonous red cell nucleoside triphosphates (NTP) ATP and GTP (guanosine triphosphate) strongly depress O2 affinity of the stripped (cofactor-free) Hb and increase cooperativity in O2 binding. As previously found in teleost Hbs, GTP exerts a greater effect than ATP at the same concentration. Urea, in contrast, increases O2 affinity and depresses cooperativity. It also antagonizes the modulator effectivity of NTP at physiological NTP/Hb concentration ratios. Deoxygenation of the Hb raises blood pH. This Haldane effect contrasts with earlier findings for Pacific specimens, but accords with the presence of a Bohr effect (phi = delta log P50/delta pH). S. acanthias Hb resolves into six main components (three pairs) on the basis of isoelectric point. There is no evidence for radical functional differentiation as found in teleosts with electrophoretically anodal and cathodal Hb components. The physiological implications of the findings and the possible molecular mechanisms basic to the NTP and urea effects are discussed.

Effects of exercise stress on acid-base balance and respiratory function in blood of the teleost Tinca tinca

We measured the effects of severe, short-term exercise stress on the acid-base balance, the O2 transporting properties and the cofactors for O2 binding in the blood of tench, Tinca tinca. Short-term severe exercise resulted in a drastic decrease in arterial blood pH which is attributed to a mixed respiratory and metabolic acidosis. Concomitantly arterial PO2 rose in apparent compensation for the detrimental effects of the acidosis on O2 transport by the blood.

Oxygenational properties and phosphorylated metabolic intermediates in blood and erythrocytes of the dogfish, Squalus acanthias

A typical whole blood O2-equilibrium curve from Squalus acanthias had a P50 of 13.2 mmHg and was slightly sigmoidal, having an n value of 1.6 at 15 degrees C, PCO2 = 2.2 mmHg (pH = 7.85). A small Bohr effect was present (phi = −0.28) together with a weak Haldane effect and no Root shift. The predominant trinucleotide, determined by thin layer chromatography, was ATP (0.44 +/− 0.13 S.D. mmol 1(−1) blood) with smaller amounts of GTP present (0.07 +/− 0.02) S.D. mmol 1(−1). Total nucleotide concentrations, determined enzymatically, were low by comparison with teleosts. Incubation of erythrocytes with or without oxygen, or in the presence of a metabolite-enriched ‘cocktail’ showed limited potential for phosphate cofactor regulation of blood oxygen affinity.

Functional characterization of hemoglobins from South Brazilian fresh water teleosts--II. Three cichlids (Crenicichla lepidota, Aequidens port alegrensis and Geophagus brasiliensis)

Oxygen equilibria of the multiple hemoglobin (Hb) from the South American cichlid fishes Crenicichla lepidota, Aequidens portalegrensis, and Geophagus brasiliensis were measured at three different temperatures (10, 20 and 30 degrees C). The cofactor-free whole hemolysates exhibited extremely high O2 affinities (half-saturation oxygen tension, P50 approximately 1 mm Hg at pH 7.2 and 20 degrees C), exceptionally large Bohr effects (phi = delta log P50/delta pH = -1.1 to -1.3 at pH 7.2-6.2 and 20 degrees C), low cooperativity, and a low sensitivities to ATP. The O2 affinities showed high thermal sensitivity (delta H for the overall oxygenation reactions were -71 to -79 kJ mol-1 at pH 8.0). Nine Hb components separated from Geophagus showed similar, if not identical, functional properties. The oxygenation properties of the Hb systems, particularly the high thermal and pH sensitivities, are interpreted as adaptions to large diurnal variations in ambient temperature, oxygen tension and activity patterns of the fish in nature.

Functional characterization of hemoglobins from South Brazilian freshwater teleosts--I. Multiple hemoglobins from the gut/gill breather, Callichthys callichthys

The five main hemoglobins of the South Brazilian bimodal breathing teleost, Callichthys callichthys were separated, and their oxygenation properties and those of the unfractionated hemolysate were measured at 10, 20 and 30 degrees C. The cathodal Hb component had a higher O2 affinity than the other components and a lower Bohr effect (phi = delta log P 50/delta pH), which is reversed at low and high pH values (6.8 greater than pH greater than 7.8). The other, anodal hemoglobins had normal Bohr effects and similar functional properties. The erythrocytic cofactor ATP had no significant effects on the O2 affinities of the hemolysate and the isolated anodal components at physiological pH conditions, but decreased the affinity of the cathodal Hb over the entire pH range tested (6.5-8.2). All hemoglobins showed high thermal dependence of O2 affinity (delta H values between -62 and -74 kJ mol-1 at pH 8.0), which decreased with falling pH, in accordance with an inverse relation between the Bohr effect and temperature. The possible adaptive significance of the oxygenation patterns of the hemoglobins and their temperature dependences are discussed comparatively with special reference to the closely-related bimodal breather Hoplosternum littorale, and to breathing habit (gill breathing in winter when the fish is a benthic feeder and "gut" air breathing in the warm reproductive season when they nest at the surface).

A computerized assisted pharmacy automatic stop order procedure

Automatic stop orders, which still seem to plague many hospitals, can be instituted with the cooperation of the medical staff, legal counsel, nursing service, and administration. The use of a computerized assisted pharmacy system, described here, allows compliance with Joint Commission on Accreditation of Hospitals' regulations and also prevents possible legal complications. By utilizing computer-generated reports, appropriate labels, and a drug order entry system for entering a discontinue/renewal time and date, compliance with established policies is possible.

Oxygen equilibrium properties of blood and hemoglobin of fetal and adult Weddell seals

Oxygen equilibria of whole blood and hemoglobins from adult and fetal Weddell seals are reported. The maternal blood shows a lower O2 affinity than the fetal blood (halfsaturation O2 tension P50 = 26.9 +/- 1.18 and 21.4 +/- 1.25 Torr, respectively, at 37 degrees C and pH 7.4), and a greater Bohr effect (delta log P50/delta pH = -0.49 and -0.31, respectively, at pH 7.4-6.8), correlated with higher red cell 2,3-diphosphoglycerate (2,3-diphosphoglycerate (2,3-DPG) concentrations (6.45 +/- 0.81 mmol.1-1, compared to 2.65 +/- 0-42 mmol.1-1 in the fetus). Both the maternal and fetal erythrocytes contain two major and two minor hemoglobin components occurring in the same ratio and the 2,3-DPG-free whole hemolysates, as well as the isolated major components from each stage, show the same oxygenation properties, ascribing the whole-blood differences to the higher adult DPG levels. A 2,3-DPG effect also appears to account for the disparity in the Bohr effects, which will favor unloading of O2 from the maternal circulation during diving as maternal and fetal blood pH decrease in parallel.

Respiratory properties of whole blood and hemoglobin from the burrowing reptile, Amphisbaena alba

Respiratory properties of whole blood and hemoglobin solutions have been studied in the burrowing reptile, Amphisbaena alba. Whole blood is distinguished from that of other squamate reptiles by an extraordinary high O2 affinity (P50 = 12 mmHg at pH 7.60 and 25 degrees C). The Bohr factor, phi, was large at -0.85 and the n-value was 1.80. O2 capacity averaged 12.0 vol%. The molar concentration of erythrocyte ATP was high and twice that of hemoglobin. Stripped Amphisbaena hemoglobin shows an extremely high O2 affinity and reduced pH sensitivity compared to whole blood (P50 = 1 mmHg at pH 7.60 and 25 degrees C, phi = -0.35, n-value = 2.0). The hemoglobin O2 affinity was much more sensitive to ATP than for other poikilotherm vertebrates. Isoelectric focusing revealed a multicomponent hemoglobin with the major components showing similar O2 affinities and Bohr shifts. The data obtained are discussed in relation to the burrowing habits of Amphisbaena and found to be adaptive to a fossorial mode of life.

pH and haemoglobin oxygen affinity in blood from the Antarctic cod Dissostichus mawsoni

Blood pH in the antarctic cod (Dissostichus mawsoni) and in two Trematomus species, occlrring at --1-9 degrees C, is extremely high (approximately 8-2 to 8-3). This supports and extends Rahn's (1966) model for the temperature-pH relationship in cold-blooded vertebrates. The blood of D. mawsoni shows a low oxygen affinity (P50 approximately equal to 14-5 mmHg at pH 8–16 and −1-9 degrees C). Despite normal in vitro temperature and pH sensitivities, blood P50 increases only slightly when live fish are temperature-stressed (+ 4-0 degrees C), or become acidotic as a result of agitational stress (blood pH 7–71), primarily as a result of compensatory decreases in blood ATP levels. Oxygen-binding properties of ‘stripped’ (cofactor-free) solutions of D. mawsoni haemoglobin were measured in attempts to elucidate the molecular mechanisms involved in the function of the pigment.

Blood respiratory properties of rainbow trout (Salmo gairdneri) kept in water of high CO2 tension

1. Blood O2 transport and acid-base balance were studied at 20 degrees C in rainbow trout (Salmo gairdneri) which had been kept in water of high CO2 content (15 mmHg) for at least a week. Also the blood gas chemistry of fish rapidly entering or leaving the hypercapnic environment was studied. 2. Fish entering high CO2 water suffered a sharp decrease in blood pH which significantly reduced O2 transport by the blood, but after a few hours considerable compensation was achieved. 3. After at least a week in high CO2 water, trout showed elevated plasma bicarbonate and PCO2 levels, and a decrease in plasma chloride, while pH was about 0 - 1 pH unit below the level for control fish. Oxygen transport by the blood was marginally reduced. 4. Hypercapnic fish rapidly entering fresh water showed a sharp increase in blood pH and a decrease in blood PO2. These parameters regained normal values after a few hours but plasma bicarbonate and chloride levels took much longer to regain control concentrations. 5. Acid-base balance in hypercapnic fish is discussed with particular reference to the role of the branchial ion exchanges.

Oxygen-binding properties of hemoglobins from estivating and active African lungfish

The oxygen-binding characteristics and the multiplicity of the stripped hemoglobiin from active lungfish Protopterus amphibius, are the same as in specimens that have been estivating for about 30 months, showing that alteration in the hemoglobin molecules is not involved in the earlier reported increase in oxygen affinity of whole blood during estivation (Johansen et al., '76). At pH 7.0 and 26 degrees C the hemolysates show a high oxygen affinity (P50 = 3.1 Torr), a Bohr factor (delta log P50/delta pH) of - 0.33, and a cooperativity coefficient (n) of 1.7. Between 15 and 26 degrees C, the apparent heat of oxygenation (delta H) is - 8.6 Kcal-mole-1 at pH 7.0, corresponding with data for other fish. A low sensitivity of oxygen affinity to urea appears to be adaptive to the high urea concentrations in estivating lungfish. The salt sensitivity is, however, similar to human hemoglobin. The hemoglobin consists of two major (electrophoretically anodal) components, which differ slightly in oxygen affinity but are both sensitive to pH and nucleoside triphosphates (NTP). Guanosine triphosphate (GTP), the major erythrocytic organic phosphate, however, depresses the oxygen affinity of the composite and separated hemoglobins more effectively than ATP suggesting that GTP is the primary modulator of oxygen affinity. Comparative measurements reveal only one major hemoglobin component in P. annectens which has a markedly lower oxygen affinity and phosphate sensitivity than P. amphibius hemoglobins and thus seems less pliable to phosphate-mediated variation in oxygen affinity. The data are discussed in relation to the hemoglobin systems of other fish.

Blood respiratory properties in the naked mole rat Heterocephalus glaber, a mammal of low body temperature

Respiratory properties of whole blood and Hb solutions have been studied in Heterocephalus glaber, a fossorial rodent, having a low body temperature (30.0-32.0 degrees C) and poor thermoregulatory ability. For comparison similar, measurements were made on laboratory mice, Mus musculus. Whole blood showed a distinctly higher O2 affinity for Heterocephalus at both 30 and 37 degrees C.P50 values were 23.3 mm Hg and 33.0 mm Hg at 37 degrees C for Heterocephalus and Mus, respectively, while at 30 degrees CP50's were 18.8 mm Hg and 24.9 mm Hg, all values at pH (b) 7.4. deltaH values (expressive of the effect of temperature on P50) were -5.8 kcal-mol-1 for Heterocephalus and -7.5 kcal-mol-1 for Mus. The CO2 Bohr effects (omega) were -0.43 and -0.50 for Heterocephalus at 37 and 30 degrees C. Corresponding values for Mus were -0.65 and -0.56. Both species had a Hill's n-value of 2.6. Red cell concentrations of 2,3-DGP were closely similar in the species being 7.3 mmol-L-1 rbc for Heterocephalus and 7.4 mmol-L-1 rbc for Mus. Stripped Heterocephalus Hb had a very high O2 affinity, at pH 7.25, 37 degrees C,P50 was 8.0 mm Hg whereas the corresponding value for Mus was 11.3 mm Hg. Addition of DPG to stripped Hb from the two species decreased O2 affinity to the same degree. The high O2 affinity of Heterocephalus blood is viewed as a possible adaptation to its burrowing habits. Its basis is inherent to the hemoglobin molecule itself and not dependent upon cofactor influence or the temperature sensitivity of the O2-Hb binding.

Temperature acclimation and oxygen-binding properties of blood and multiple haemoglobins of rainbow trout

Acclimation of rainbow trout to 5, 15 and 22 degrees C for periods exceeding 4 months had no significant effect on the oxygen affinity of whole blood or on the concentration of ATP, which is the main organic phosphate in red cells. Slight differences were, however, found in the oxygenation properties of the haemolysates, which correlate with changes in the relative concentration of the multiple haemoglobins. The oxygen-binding properties of the main haemoglobin components account for the observed differences in the haemolysates. The possible thermoacclimatory significance of changes in haemoglobin multiplicity and co-factor concentrations is discussed.

Respiratory properties of blood in awake and estivating lungfish, Protopterus amphibius

Blood respiratory properties have been studied in awake and estivating African lungfish, Protopterus amphibius. Fish had been estivating 28-30 months when blood was sampled. Hematocrit, O2 capacity and blood hemoglobin concentration increased by about 50% during estivation. Red cell Hb concentration (MCHC) was unaltered. Total blood concentration of nucleoside triphosphates (NTP) was reduced 50% in estivation. Thin-layer chromatography showed that the change in NTP resulted from a GTP/Hb (guanosine triphosphate) reduction to 20% of the value in awake fish. ATP (adenosine triphosphate) concentration remained largely unaltered. GTP/Hb changes were accompanied by marked changes in O2 affinity. The P50 value in blood from awake fish was 33 mm Hg at pH 7.5 compared to 9 mm Hg for the estivating fish. The n-value changed insignificantly. An increased Bohr effect was present in estivating fish, but its importance will depend on circulating pH in the two states. Standard bicarbonate ranged from a low of 8.6 mMol-L-1 (P plasma) at pH 7.5 in an awake fish to 49.6 mMol-L-1 (P) in an estivating fish. CO2 dissociation curves showed a variable Haldane effect having its highest value in the in vivo range of PCO2. The striking increase in O2-Hb affinity during estivation is regarded as an adaptation to a reduced alveolar O2 availability associated with estivation. Altered mechanics of pulmonary ventilation and reduced ambient O2 availability caused by the subterranean habitat may have been selection pressures for the development of the high O2 availability caused by the subterranean habitat may have been selection pressures for the development of the high O2 affinity. The mechanism behind it rests with the recorded change in erythrocytic concentration of GTP.

The hemoglobin system of the primitive fish, Amia calva: isolation and functional characterization of the individual hemoglobin components

Blood from the primitive holostean fish, the bowfin, Amia calva, contains 2 mo of ATP per mol of hemoglobin. The hemolysates contain at least five tetrameric hemoglobin components which differ in their oxygen affinities and their response to cofactors such as ATP. The binding of oxygen by each chromatographically isolated component, including a cathodal component, is influenced by pH and organic phosphates; there is no significant differentiation of function or structure as seen in trout and certain other fish hemolysates. Kinetic analyses of ligand binding indicate that the Bohr and Root effects of Amia calva hemoglobins are best explained by changes in both the "on" and "off" constants. At low pH, the increase in the "off" constant is smaller than for most other Root hemoglobins. The hemoglobin system of Amina calva is functionally undifferentiated and may be representative of the ancestral condition in teleosts.