Non-bicarbonate Buffer Research Articles

Respiratory properties of the blood of the little penguin Eudyptula minor

1. 1. Oxygen and CO 2 carriage and buffering capacity were studied in blood from little penguins ( Eudyptula minor). 2. 2. Hill plots were linear over a wide range of O 2 saturation, with a Hill coefficient of 3.2. Half saturation pressure (P 50) was 35.1 torr. Fixed acid Bohr effect was low (− 0.39), and mean Haldane effect was 0.34 mol CO 2/(mol O 2). 3. 3. pK' of the bicarbonate buffer system was 6.086. 4. 4. Buffering capacities of whole blood (20.8 mmol/1/pH) and plasma (22.3 mmol/1/pH) were similar to most other birds, but much lower than other penguins. 5. 5. The low non-bicarbonate buffer capacity and high Hill coefficient may act to increase oxygen unloading during dives.

Heat Dissipation, Gas Exchange and Acid-Base Status in the Land Snail Oreoheux During Short-Term Estivation

ABSTRACT Within 4 days following entry into estivation, heat dissipation and oxygen consumption by the land snail Oreohelix spp. decreased by 83% compared to standard non-estivating rates. During both non-estivating and estivating conditions, the quantity of heat dissipated per mole of O2 consumed was indicative of a completely aerobic metabolism. This calorimetric-respirometric (C/R) ratio was –461 ±12 kJ mol−1O2 (S.E.M., N=5) under standard non-estivating conditions and –464±26kJmol−1O2 (N=4) during estivation. Respiratory exchange ratios reflected a primary dependence upon carbohydrate as a metabolic substrate during both states. Carbon dioxide retention occurred during the first 36h of estivation, resulting in an increase in hemolymph and a decrease in pH. The respiratory acidosis during short-term estivation was not compensated by elevation of hemolymph [HCO3−] above levels predicted from the in vitro non-bicarbonate buffer value of hemolymph. A brief period of rapid CO2 release, which caused hemolymph and pH to return to pre-estivation values, preceded the increase in O2 consumption during arousal. Exposure of nonestivating snails to 4.67 kPa (1 kPa=7.5mmHg) caused a rapid and fully reversible 50% suppression of respiration rate. The temporal nature of CO2 retention and release during entry into and arousal from estivation, and the suppression of O2 consumption by artificial hypercapnia, support the hypothesis that elevated or the resultant acidosis may contribute to metabolic suppression during estivation by land snails.

Determination of intracellular buffer values after metabolic inhibition by fluoride and nitrilotriacetic acid

Non-bicarbonate buffer values have been analysed in homogenates of squid mantle muscle and toad gastronemius muscle using the P CO 2 equilibration technique. Homogenate metabolism was inhibited by the addition of potassium fluoride and nitrilotriacetic acid. After and initial change in the concentration of organic phosphates a new metabolic equilibrium was achieved which was insensitive to pH changes during P CO 2 variations. Inaccurate measurements of homogenate buffer values could, thereby, be prevented. The accumulation of inorganic phosphate during the initial metabolic shift caused an increase in homogenate buffer values. Levels of unbound inorganic phosphate, which are effective in buffering, were estimated by enzymatic analysis in homogenate ultrafiltrates. Based on the evaluation of apparent dissociation constants pK′, and buffer values for fluoride and inorganic phosphate, the non-bicarbonate, non-phosphate i, (i:inorganic) buffer value of the tissue was calculated. The level of free inorganic phosphate in the resting tissue was considered for an estimate of the intracellular non-bicarbonate buffer value under control conditions.

CO 2 transport in agnathan blood: evidence of erythrocyte Cl −/HCO 3− exchange limitations

CO 2 transport properties of blood were examined in the lamprey Petromyzon marinus and the hagfish Myxine glutinosa. In order to evaluate possible chloride/bicarbonate exchange limitations, experiments were conducted under control conditions and in the presence of an ionophore to permit equilibrium distribution of chloride, bicarbonate, and protons across the erythrocyte membrane. The ionophore, tri- n-propyl tin chloride, markedly altered the CO 2 transport properties and apparent nonbicarbonate buffering characteristics of the blood of Petromyzon marinus. In addition, the distributions of protons, bicarbonate and chloride ions across the erythrocyte membrane were very different from each other under control conditions, but became very similar in the presence of the anionic ionophore. The CO 2 transport properties of the blood of Myxine glutinosa were not significantly different in the presence of the ionophore. Small but significant changes were observed, however, in erythrocyte pH, chloride concentration and water content in the presence of tri- n-propyl tin chloride. These results demonstrate that chloride/bicarbonate exchange limitations and possibly active transport of protons contribute to the unique CO 2 transport properties in the blood of the lamprey, Petromyzon marinus. In the hagfish, Myxine glutinosa, the importance of anion exchange limitations or active proton transport with regard to the CO 2 carrying properties of the blood are clearly much less than in the lamprey under the in vitro conditions of this study.

Buffering characteristics of eel blood at the extreme conditions in the swimbladder

CO 2 binding in whole blood and true plasma of the eel was estimated by measuring CO 2 content and pH in blood aliquots equilibrated with various P CO 2 values over a wide range expected to occur in the swimbladder. Bicarbonate concentration, [HCO 3 −], was calculated using the CO 2 solubility coefficient, which was measured to average 50 μmol·L −1·Torr −1 (20°C). Buffer lines of non-bicarbonate buffers were obtained in plots of [HCPO 3 −] against pH, and non-bicarbonate buffer values, β NB, were obtained by curve. fitting. In the pH range 6.6–8.2, the buffer line for oxygenated whole blood was sigmoid, while that for deoxygenated blood increased its slope monotonously with increasing pH. The β NB for oxygenated blood displayed a maximum of about 8.6 mmol·L −1pH −1 at pH = 7.4 and dropped down to below 1 mmol·L −1·pH −1 at higher and lower pH. Similar shapes of the buffer lines were obtaned in true plasma; the [HCO 3 −] levels and β NB values were, however, somewhat higher than in whole blood. These data are useful fo assess the back-diffusion of CO 2 and HCO 3 − in the rete mirabile of the fish swimbladder and to estimate the effects CO 2 back-diffusion exerts on the counter-current enhancement of O 2 in the rete.

The Absence of Rapid Chloride/Bicarbonate Exchange in Lamprey Erythrocytes: Implications for CO2 Transport and Ion Distributions Between Plasma and Erythrocytes in the Blood of Petromyzon Marinus

ABSTRACT Carbon dioxide transport and ion distributions were examined in the blood of the lamprey, Petromyzon marinus. Over the range studied, the erythrocytes had the highest total CO2 content, followed by whole blood and true plasma. The nonbicarbonate buffer values were —37·0mequivl-1pHunit-1 for erythrocytes, —3·3mequivl-1pH unit-1 for whole blood and —0·1mequivl-1 pH unit-1 for true plasma. These results are in sharp contrast to the models of carbon dioxide transport in the blood of other vertebrates and are consistent with the view that chloride/bicarbonate exchange is virtually absent in agnathan erythrocytes. Protons are passively distributed in Petromyzon blood. However, the distribution ratio for chloride between plasma and erythrocytes was strikingly different from the distribution ratio for protons. In the absence of rapid chloride/bicarbonate exchange, the erythrocyte volume is relatively constant over the physiological pH range. A model is presented to explain carbon dioxide transport in lamprey blood which does not involve a rapid chloride/bicarbonate exchange mechanism on the erythrocyte membrane.

Adaptations to a Terrestrial Existence by the Robber Crab Birgus Latro: I. An in vitro Investigation of Blood Gas Transport

ABSTRACT The gas-transporting properties of the haemolymph of Birgus latro L. were investigated in vitro. This terrestrial anomuran is restricted in distribution to the tropics, and on Christmas Island inhabits a highly stenothermal environment. The effect of temperature on haemocyanin oxygen-affinity was pronounced (ΔH = –39 kJ mol−1) and was considered to represent the absence of any specific adaptation to environmental temperature. The Bohr effect was large for a terrestrial decapod (ϕ = –0·60), although reduced at low pH. Changes in [Ca] had a significant effect on oxygen affinity of dialysed haemolymph (ΔlogP50/ Δlog[Ca] = –0·39) whereas [Mg] had no effect. Increasing, [L-lactate] had a small effect on the oxygen affinity of dialysed haemolymph (ΔlogP50/ Δlog[lactate] =–0·013) but not whole haemolymph. Dialysis increased oxygen affinity, suggesting the presence of a dialysable component that suppresses affinity. The effect of L-lactate was inhibited in whole haemolymph. The oxygen affinity of Birgus haemolymph was largely insensitive to effector substances, with the possible exception of Ca. In the case of lactate, at least, this was not due to a reduced sensitivity of the haemocyanin, a situation different from that in closely related species. Carbon dioxide transport was also affected by temperature. Birgus haemolymph showed a high nonbicarbonate buffer capacity which could be correlated with a high haemocyanin concentration. It is concluded that terrestrial anomuran decapods depend on mechanical adjustments of ventilation and perfusion, rather than employing direct modulation of haemocyanin function, to optimize oxygen delivery.

Dissociation of acid-base effects on substrate accumulation and on delta pH in dog mitochondria.

The relationship between the pH gradient (delta pH) and substrate accumulation was examined in mitochondria from dog renal cortex. Mitochondria were incubated in media containing bicarbonate or nonbicarbonate buffers. Mitochondrial delta pH was at equilibrium after 2 min incubation but citrate accumulation in the matrix space was still increasing. With nonbicarbonate buffer in rotenone-inhibited mitochondria, citrate and alpha-ketoglutarate concentrations in the matrix did not vary between pH 7.5 and 7.1; delta pH decreased from 0.62 to 0.52 as medium pH fell. With decreasing bicarbonate concentration (from 40 to 10 mM) and constant CO2 tension, concentrations of citrate, alpha-ketoglutarate, malate, glutamate, glutamine, and formate increased; pyruvate accumulation was lower at 10 than at 25 mM bicarbonate; delta pH remained constant. When respiratory changes were produced, concentrations of citrate, alpha-ketoglutarate, malate, and glutamate increased as medium pH fell and CO2 tension increased; accumulation of pyruvate, glutamine, and formate was unaffected. delta pH fell from 0.48 to 0.39 as CO2 tension rose from 3 to 12%. In uninhibited mitochondria, 14CO2 formation from labeled citrate was greater with 10 than with 40 mM bicarbonate; this difference as well as the accumulation of citrate in the matrix was blocked by inhibition of the tricarboxylate carrier with 1,2,3-benzenetricarboxylate. These results dissociate effects of acid-base change on mitochondrial substrate accumulation from changes in delta pH. They suggest a direct, bicarbonate-dependent influence of pH on multiple mitochondrial substrate carriers. This phenomenon may play an important role in metabolic regulation in renal cortex.

The effect of one-legged sprint training on intramuscular pH and nonbicarbonate buffering capacity.

To determine the effect of one-legged sprint training on muscle pH and nonbicarbonate buffering capacity (BC), 9 subjects completed 15 to 20 intervals at 90 RPM, 4 days a week for 7 weeks on a bicycle ergometer adapted for one-legged pedaling. Needle biopsies from the vastus lateralis and blood samples from an antecubital vein were taken at rest and twice during recovery (1 and 4 minutes) from a 60 s one-legged maximal power test on a cycle ergometer. pH one minute after exercise in both the trained and untrained legs following the training period was not different but both were higher than before training. BC increased from 49.9 to 57.8 mumol HCl x g-1 x pH-1 after training (p less than 0.05). Blood lactate levels after exercise were significantly higher for the trained leg when compared to the untrained leg after spring training. Peak and average power output on the 60 s power test increased significantly after training. One-legged aerobic power (VO2max) was significantly increased in the untrained and trained legs. Two-legged VO2max also improved significantly after training. These data suggest that nonbicarbonate buffering capacity and power output can be enhanced with one-legged sprint training. Also, small but significant improvements in VO2max were also observed.

L-Lactate affects CO 2 transport in crustacean haemolymph

1. 1. A comparative study of carbon dioxide capacitance and buffer capacity of the haemolymph of the decapod crustaceans Ocypode saratan, Carcinus maenas and Palaemon elegans has been carried out. 2. 2. The relationship between the total carbon dioxide content of the blood ( C CO 2) and the pH of the haemolymph was examined. Values for [HCO 3 −] obtained by subtraction of the dissolved CO 2 from C CO 2 were compared with those derived using a constant p K1 value according to the Henderson-Hasselbalch equation. 3. 3. In Carcinus, but not in Palaemon the use of a constant p K1 over-estimated the non-bicarbonate buffer value and under-estimated CO 2 capacitance at high pH. 4. 4. Results obtained for Ocypode were similar to those obtained for Carcinus haemolymph except that increasing the l-lactate concentration in the haemolymph resulted in a marked reduction of the buffer value as estimated by the Henderson-Hasselbalch equation. This was in contrast to the constant buffer value calculated using measured values. 5. 5. Differences between the calculated and observed buffer value of the haemolymph could be attributed to a pH dependence of p K1. 6. 6. The possibility that haemocyanin-CO 2 binding contributes to the CO 2 capacitance of the haemolymph in a manner which is not predicted by the Henderson-Hasselbalch equation and that this component is dependent on pH and possibly on the lactate concentration is discussed.

The effect of prolonged hypoxia on striated muscle pH regulation.

The extracellular acid-base status of mammals exposed to low inspired PO2 for prolonged periods of time has been studied extensively (Bouverot, 1985). However, less is known regarding the intracellular acid-base status during prolonged hypoxia. In a previous study we observed that the intracellular pH of striated muscles of rats subjected to 3 weeks of hypobaric hypoxia was not significantly different from that of normoxic rats (Gonzalez and Clancy, 1986b). However, when the cells were acid-loaded by rendering the animals hypercapnic, the decreases in intracellular pH of tibialis anterior, quadriceps and diaphragm were significantly less than in hypercapnic normoxic rats. The magnitude of cell pH regulation, as measured by the apparent non-bicarbonate buffer value, ranged from 3 (tibialis anterior) to 12 (diaphragm) times greater in the hypobaric hypoxic than the normoxic animals. This augmentation of striated muscle pH regulation during hypercapnia in hypobaric hypoxic rats could result from increased physicochemical buffering and/or increased efflux of proton equivalents. The question arises as to whether augmentation of these cellular pH- regulating mechanisms resulted from intrinsic changes in the cell interior and/or the sarcolemma engendered by the prolonged hypoxia or whether extracellular factors which enhance these cellular pH-regulating mechanisms were increased to a greater extent in the hypercapnic hypoxic rats than in the hypercapnic normoxic rats. To resolve this question cell pH regulation of diaphragms from prolonged hypoxic and normoxic rats was studied under in vitro conditions. Under these conditions the contribution of extracellular factors to cell pH regulation was the same in diaphragms from hypoxic and normoxic rats. Therefore, any difference in cell pH regulation should be attributable to intrinsic changes in one or more of the cell pH-regulating mechanisms.

Acid-base regulation and blood gases in the anuran amphibian, Bufo marinus, during environmental hypercapnia.

Specimens of Bufo marinus were exposed to aerial and aquatic hypercapnia (5% CO2) in a closed, water recirculation system to evaluate mechanisms involved in the compensation of a respiratory acidosis in these animals. Arterial PCO2 was elevated from about 9 mmHg (1 mmHg = 133.3 Pa) to 35 (1 h) and 37 mmHg (2 h), and gradually approached about 40 mmHg (24 h of hypercapnia). The typical hypercapnia-induced reduction in plasma pH from about 7.9 to below 7.4 was partially offset, at least during the first hours of hypercapnia, by a reduction in the inspired/arterial PCO2 difference, presumably brought about by pulmonary hyperventilation. The predominant contributor to extracellular pH compensation, however, was a net gain of bicarbonate from the environment, mainly facilitated by ammonia excretion. Bicarbonate originating from the environment was accumulated in the body fluids, increasing the plasma concentration from the control of about 9 to 36 mmol l-1 after 24 h. Extracellular pH was compensated to only about 30% of the shift expected at constant bicarbonate level and, according to the steady reduction of pH, non-bicarbonate buffering of CO2 also contributed significantly to the elevation of bicarbonate. This relatively poor pH compensation (compared with fishes) could not be improved either by direct administration of bicarbonate into the bloodstream or by increased environmental ion concentrations. It is concluded that the availability of bicarbonate is not a limiting factor for pH compensation during hypercapnia, and that the inability of Bufo to accumulate bicarbonate to concentrations sufficient for better hypercapnia compensation is based on a constitutional 'bicarbonate threshold' of the resorbing and retaining structures for acid-base-relevant ions.

Physiological Responses of the Rock Crab Cancer irroratus (Say) to Environmental Hyperoxia. I. Acid-Base Regulation

Hemolymph acid-base and ion levels and acidic equivalent exchange with the experimental water were monitored in rock crabs (Cancer irroratus Say) exposed to control normoxia (PIo2 ≃ 150 torr), 48 h of hyperoxia (Po2 ≃ 512 torr), and 24 h of subsequent normoxic recovery. Hemolymph CO₂ binding was assessed in vitro on oxygenated and deoxygenated samples. Settled normoxic crabs had the following acid-base status: pH—8.01; Pco2—2.1 torr, and [HCO₃⁻]-9.3 meq·liter⁻¹ and appeared to be in proton balance with the experimental water. Within 6 h of exposure to hyperoxia, the hemolymph exhibited a significant acidosis (0.15 pH units) that was due to respiratory CO2 (Pco2 increased by 50%). This acid-base imbalance was restored between 6 and 24 h by a 50% increase in [HCO₃⁻]. This coincided with a 13-fold increase in excretion of acidic equivalents (primarily titratable) into the experimental water that continued for up to 10 h. Numerically, there was excellent correspondence between acid efflux and the magnitude of the extracellular proton load. Although crabs continued to hypoventilate, preexperimental Pco2 was reestablished by 24 h, suggesting that the original hypercapnia had been due to a perfusion limitation. Between 24 and 48 h, circulating [HCO₃⁻] was also restored to resting levels accompanied by an equivalent net base excretion into the bathing medium. When normoxia was reinstated, hemolymph exhibited a reduction in Pco2 plus a further reduction in [HCO₃⁻] at constant Pco2, making pH alkalotic. The base efflux that persisted into the recovery period significantly exceeded that required to restore extracellular acid-base balance. It is suggested that this base load originated intracellularly and that the reduced cardiac output during hyperoxia limited its removal into the hemolymph. Circulating lactate exhibited a similar washout effect during recovery. Hemolymph of C. irroratus had a low nonbicarbonate buffer value (β) corresponding to reduced protein concentration. However, the Haldane effect, which theoretically could account for the release of 2.13 mmol CO2 per mmol O2 bound, was larger than observed in other decapods.

Blood osmolality in vitro: dependence on base addition, buffer value, and temperature.

Blood osmolality (Osm) increases with PCO2 because of CO2 absorption. The influences of NaOH addition, equilibration temperature, and hemoglobin concentration on these respiratory changes of Osm were measured by freezing-point determination in true plasma. Addition of NaOH increases Osm by 2 mosmol X kg H2O-1 X mmol base-1 X l at constant PCO2 due to the osmotic effects of Na+ and produced bicarbonate. Respiratory compensation of the pH change further increases Osm. This contrasts to the respiratory compensation of the osmolar disturbance caused by fixed acid. Raising the equilibration temperature reduces Osm by 0.5 mosmol X kg H2O-1 X degrees C-1 at constant pH mainly caused by a lower absorption coefficient for CO2 and changed pK value for H2CO3. The slope of the linear regression lines between Osm and pH during CO2 equilibration increases with hemoglobin; the value of the quotient delta Osm/delta pH depends directly on the nonbicarbonate buffer value. The use of this quotient for the estimation of the mean nonbicarbonate buffer value of the whole body is suggested. The osmotic effects of therapeutic base infusion should be regarded with caution.

Distal tubule bicarbonate accumulation in vivo. Effect of flow and transtubular bicarbonate gradients.

We have performed microperfusion studies on distal tubules of normal and alkalotic rats in an attempt to demonstrate in vivo bicarbonate secretion. All perfusion solutions were free of phosphate and other nonbicarbonate buffers. In both normal and alkalotic rats, distal perfusions elicited significant tCO2 entry only at high flow (24 nl/min). Even when perfusate tCO2 concentration closely matched plasma tCO2 concentration (30 mM tCO2), significant tCO2 entry again occurred at high flow. This was associated with a rise of the perfusate tCO2 concentration, which indicated net entry of tCO2 against a concentration gradient. In this "symmetrical" perfusion situation, acetazolamide blockade prevented tCO2 entry. Accordingly: distal tubule tCO2 entry is demonstrable in both alkalotic and normal rats at high flow rates; increasing perfusate tCO2 concentration can suppress tCO2 entry; and entry can occur in the absence of a gradient and this effect can be blocked by acetazolamide.

Intracellular pH regulation during prolonged hypoxia in rats

Conscious rats maintained for three weeks at PB 370–380 Torr were studied in a chamber where PI O2 was maintained at 68–70 Torr at ambient barometric pressure (740–750 Torr). Controls were pair-fed rats maintained at ambient barometric pressure and studied at ambient PI O2 (normoxia). In approximately half of the hypoxic and normoxic animals, hypercapnia was induced by increasing PI O2 for 4 h. Steady-state intracellular pH (pHi) of left and right ventricle, and of tibialis anterior, quadriceps and diaphragm was determined from the distribution of 5,5-dimethyl-2,4-oxazolidinedione (DMO). Apparent non-bicarbonate buffer value (βapp) was calculated as the ratio of the change in HCO 3 − concentration to the change in pH elicited by the increase in P CO 2 . βapp of plasma, tibialis anterior, quadriceps and diaphragm was approximately 2, 3, 6 and 12 times higher, respectively, in hypoxic than in normoxic rats. Neither left nor right ventricular βapp was significantly changed by prolonged hypoxia. In the hypoxic animals, bilateral nephrectomy abolished the increase in βapp of plasma, tibialis anterior and quadriceps, and moderated the increase in βapp of diaphragm. No significant effect of nephrectomy was observed in βapp of either left or right ventricle. The results indicate that in the skeletal muscles studied under conditions of an acid load in the form of increased P CO 2 , intracellular pH is better regulated in hypoxic than in normoxic rats. The effects of nephrectomy suggest that this is due, at least in part, to a more effective renal compensation in hypoxic than in normoxic rats. Prolonged hypoxia, on the other hand, does not affect the cell pH regulation of right or left ventricle.

Renal compensation of hypercapnia in prolonged hypoxia

We previously showed that rats made hypoxic for three weeks were able to regulate their plasma pH better than normoxic rats during acute hypercapnia. This improved pH regulation was abolished by nephrectomy, suggesting that it was due, at least in part, to a more effective renal compensation of hypercapnia in hypoxic rats. To test this possibility renal acid excretion was measured in conscious rats that had been kept at PB 370–380 Torr for three weeks. The rats were studied in a chamber where PI O 2 was kept at 68–70 Torr at ambient PB (740–750 Torr). Controls were pair-fed normoxic rats. After a 2 h control period, inspired P CO 2 was increased for 4 h. The apparent non-bicarbonate buffer value of arterial blood plasma was twice as high in the hypoxic than in the normoxic rats. Renal excretion of ammonium increased to a similar extent during hypercapnia in both normoxic and hypoxic rats. Titratable acid excretion of normoxic rats did not change significantly during hypercapnia. In the hypoxic rats, on the other hand, total excretion of titratable acid in the 2 h control period was 90.9 ± 16.4 μmol/rat; and increased to 150.0 ± 13.4 μmol/rat in the first 2 h and to 232.9 ± 26.0 μmol/rat in the last 2 h of hypercapnia. In spite of this large increase in acid excretion, urine pH of hypoxic rats did not change significantly, indicating a higher buffer value of the urine of hypoxic rats. These results confirm our previous observations and support the idea that the improved pH regulation of hypoxic rats is due in part to a more effective renal compensation of hypercapnia.

Acid-base regulation in prolonged hypoxia: Effect of increased P CO 2

Conscious rats maintained for 3 wk at PB 370–380 Torr were studied in a chamber where PI O 2 was kept at 68–70 Torr at ambient barometric pressure (740–750 Torr). Blood samples were obtained through an arterial catherer. Controls were pair-fed rats maintained at ambient barometric pressure and studied at PI O 2 68–70 Torr for 4 h (acute hypoxia) or at ambient PI O 2 (normoxia). Arterial blood pH of 3-wk hypoxic rats was not different from that of normoxic rats. Hypercapnia was produced by increasing PI CO 2 for 4 h. The 3-wk hypoxic rats showed the highest apparent non-bicarbonate buffer value of arterial blood ( βapp): 77 mmol/(pH·kg), compared to 38 in normoxia and 43 mmol/(pH·kg) in acute hypoxia. Comparison of βapp at different times of hypercapnia in intact and in nephrectomized rats suggests that the high βapp of prolonged hypoxia is largely due to an increased renal compensation, and, to a smaller extent, to increased chemical buffering. While the extracellular fluid of normoxic and acute hypoxic rats showed a net gain of base of non-renal origin during hypercapnia, the 3-wk hypoxic rats showed a net non-renal base loss, which may be ,asked by the increased renal compensation.

Acid-base and respiratory properties of a buffered bovine erythrocyte perfusion medium.

Current research in organ physiology often utilizes in situ or isolated perfused tissues. We have characterized a perfusion medium associated with excellent performance characteristics in perfused mammalian skeletal muscle. The perfusion medium consisting of Krebs-Henseleit buffer, bovine serum albumin, and fresh bovine erythrocytes was studied with respect to its gas-carrying relationships and its response to manipulation of acid-base state. Equilibration of the perfusion medium at base excess of -10, -5, 0, 5, and 10 mmol X L-1 to humidified gas mixtures varying in their CO2 and O2 content was followed by measurements of perfusate hematocrit, hemoglobin concentration, pH, Pco2, Cco2, Po2, and percent oxygen saturation. The oxygen dissociation curve was similar to that of mammalian bloods, having a P50 of 32 Torr (1 Torr = 133.3 Pa), Hill's constant n of 2.87 +/- 0.15, and a Bohr factor of -0.47, showing the typical Bohr shifts with respect to CO2 and pH. The oxygen capacity was calculated to be 190 mL X L-1 blood. The carbon dioxide dissociation curve was also similar to that of mammalian blood. The in vitro nonbicarbonate buffer capacity (delta [HCO3-] X delta pH-1) at zero base excess was -24.6 and -29.9 mmol X L-1 X pH-1 for the perfusate and buffer, respectively. The effects of reduced oxygen saturation on base excess and pH of the medium were quantified. The data were used to construct an acid-base alignment diagram for the medium, which may be used to quantify the flux of nonvolatile acid or base added to the venous effluent during tissue perfusions.

Respiratory Properties of Blood From Voluntarily and Forcibly Submerged Xenopus Laevis

ABSTRACT The respiratory properties of blood from voluntarily diving Xenopus seem well matched to the animal’s habit of ventilating its lungs in an intermittent fashion. Compared with more terrestrial anurans, the high oxyhaemoglobin affinity (P50 = 29·6 Torr, pH 7·73, 25°C), Bohr effect (ΔlogP50/ΔpH = −0·37) and Haldane effect (0·37 mol CO2mol−1 O2) can be viewed collectively as adaptations towards effective blood gas storage during periods of apnoea and blood gas exchange during episodes of air breathing. It appears, therefore, that these biochemical adaptations are linked to the changes in respiratory blood flow that are made possible by the partially divided double circulation of Xenopus. In comparison with blood from voluntarily diving Xenopus, that taken from animals at the end of a 30-min enforced dive was haemoconcentrated and contained 4 and 8 mmol l−1 higher concentrations of true plasma lactate and metabolic acid equivalents respectively. The pH-induced effects of the latter led to reductions in oxyhaemoglobin affinity and blood CO2 carriage, both of which persisted for up to 4h following emergence from an enforced dive. The associated haemoconcentration led to a secondary series of effects of which the most obvious were an elevated blood oxygen-carrying capacity and an increased non-bicarbonate buffer slope for true plasma. Marked changes, such as these, were never observed in blood samples taken at various stages of voluntary dives lasting upwards of 30 min.