Low CO2 Tension Research Articles

A Carbonic Anhydrase Pseudogene Sensitizes Select Brucella Lineages to Low CO2 Tension.

Brucella spp. are intracellular pathogens that cause a disease known as brucellosis. Though the genus is highly monomorphic at the genetic level, species have animal host preferences and some defining physiologic characteristics. Of note is the requirement for CO2 supplementation to cultivate particular species, which confounded early efforts to isolate B. abortus from diseased cattle. Differences in the capacity of Brucella species to assimilate CO2 are determined by mutations in the carbonic anhydrase gene, bcaA Ancestral single-nucleotide insertions in bcaA have resulted in frameshifted pseudogenes in B. abortus and B. ovis lineages, which underlie their inability to grow under the low CO2 tension of a standard atmosphere. Incubation of wild-type B. ovis in air selects for mutations that "rescue" a functional bcaA reading frame, which enables growth under low CO2 and enhances the growth rate under high CO2 Accordingly, we show that heterologous expression of functional Escherichia coli carbonic anhydrases enables B. ovis growth in air. Growth of B. ovis is acutely sensitive to a reduction in CO2 tension, while frame-rescued B. ovis mutants are insensitive to CO2 shifts. B. ovis initiates a gene expression program upon CO2 downshift that resembles the stringent response and results in transcriptional activation of its type IV secretion system. Our study provides evidence that loss-of-function insertion mutations in bcaA sensitize the response of B. ovis and B. abortus to reduced CO2 tension relative to that of other Brucella lineages. CO2-dependent starvation and virulence gene expression programs in these species may influence persistence or transmission in natural hosts.IMPORTANCEBrucella spp. are highly related, but they exhibit differences in animal host preference that must be determined by genome sequence differences. B. ovis and the majority of B. abortus strains require high CO2 tension to be cultivated in vitro and harbor conserved insertional mutations in the carbonic anhydrase gene, bcaA, which underlie this trait. Mutants that grow in a standard atmosphere, first reported nearly a century ago, are easily selected in the laboratory. These mutants harbor varied indel polymorphisms in bcaA that restore its consensus reading frame and rescue its function. Loss of bcaA function has evolved independently in the B. ovis and B. abortus lineages and results in a dramatically increased sensitivity to CO2 limitation.

Exhaustive exercise, animal stress, and environmental hypercapnia on motility of sperm of steelhead trout (Oncorhynchus mykiss)

Motility of salmonid sperm is inhibited by the presence of carbon dioxide (CO2) in vitro; however, whether this occurs in response to challenges to the adult in vivo is not known. To determine whether CO2 negatively impacts sperm function in vivo, mature males were exposed to exhaustive exercise as well as to acute stress, chronic stress, tricaine anesthesia and environmental hypercapnia and sperm motility and semen CO2 tensions and pH values assessed. Semen CO2 rose and pH decreased significantly only in response to exhaustive exercise and environmental hypercapnia (13 kPa CO2). These changes in semen CO2 and pH were associated with reductions in numbers of sperm becoming motile upon water activation. Chronic and acute stress and tricaine anesthesia were without effect on sperm motility or on semen CO2 or pH. The time course of CO2 inhibition and recovery was evaluated in vitro. At least 50 min was required to note 50% of the inhibitory effect of low CO2 tensions on motility when sperm were exposed to 1.6-3.1 kPa CO2. At higher CO2 levels sperm motility displayed 50% of the inhibitory effect of these tensions within about 30 min. Sperm recovered maximal motility within 1 h of being placed in a nominally CO2-free environment. This study demonstrates sperm vulnerability to not only in vitro CO2 exposure but also in vivo exposure during exhaustive exercise and as result of environmental hypercapnia.

Influence of hypoxia/low glucose on carotid body release of acetylcholine

The carotid body (CB), a polymodal sensor of arterial blood, increases its neural output to the brain when stimulated by low O2 tension, pH, glucose, or high CO2 tension. Reflex cardiopulmonary responses ensue. Current reports identify acetylcholine (ACh) and ATP as two excitatory transmitters in the cat and rat CBs. This study explored the impact of hypoxia (HH), low glucose, and both together on the release of ACh and ATP from two incubated cat CBs. The CBs were prepared with standard procedures consonant with the regulations of the Institutional Animal Care and Use Committee. ACh was measured with HPLC-ECD methods. ATP was measured with luminometer for bioluminescence. Normalized to their controls, significantly increased ACh samples were recovered from the incubation medium in response to HH, low glucose, and HH+low glucose. Normalized to their controls, significantly increased ATP samples were recovered from the incubation medium in response to HH and HH+low glucose. Low glucose generated an increase in ATP which was not significant at the 0.05 level. Further, normalizing the initial challenge stage to the final control stage for both ACh and ATp generated significant increases in response to HH, low glucose (ACh only), and HH+low glucose. The data suggest the release of both transmitters is relatively constant under the conditions of the experiments. Further, they suggest the increased neural output in response to low glucose is primarily, if not exclusively, due to ACh. Supported by NIH awards from NHLBI: HL 05-0712-13, HL72293.

Regional cerebral blood flow and tissue oxygenation during hypocarbia in geese

Very low arterial CO2 tension (PaCO2) experienced by birds during high-altitude flight may result in cerebral vasoconstriction and reduced cerebral O2 delivery. To examine this possibility, we measured regional cerebral blood flow (CBF) and tissue PO2 in pentobarbital-anesthetized geese (Anser domesticus). Twenty-five-micrometer Teflon-coated platinum electrodes for H2-clearance measurements of local blood flow or tissue PO2 were implanted in the cerebral cortex in 11 geese. Tissue H2 and O2 were measured by voltage clamping the electrodes at +0.30 and -0.5 V, respectively. Washout kinetics of H2 gas administered via unidirectional lung ventilation was used to calculate local blood flow for those electrodes exhibiting one- or two-compartment washout kinetics of H2 (128 of 296 washouts in 31 electrodes). PaCO2 was controlled between 8 and 55 mmHg by altering pulmonary gas flow or by adjusting inspired PCO2. CBF decreased as PaCO2 fell from 50 to 20 mmHg but did not decrease further as PaCO2 was reduced below 20 mmHg. CBF was uniformly distributed in different regions of the cortex. Despite the plateau in CBF during severe hypocapnia, tissue PO2 continued to decline as PaCO2 fell below 20 mmHg. Severe alkalosis may limit cerebral O2 delivery in birds during high-altitude flight.

Hypoxic exposure and activation of the afterdischarge mechanism in conscious humans

After voluntary hyperventilation, normal humans do not develop a significant ventilatory depression despite low arterial CO2 tension, a phenomenon attributed to activation of a brain stem mechanism referred to as the "afterdischarge." Afterdischarge is one of the factors that promote ventilatory stability. It is not known whether physiological stimuli, such as hypoxia, are able to activate the afterdischarge in humans. To test this, breath-by-breath ventilation (VI) was measured in nine young adults during and immediately after a brief period (35-51 s) of acute hypoxia (end-tidal O2 tension 55 Torr). Hypoxia was terminated by switching to 100% O2 (end-tidal O2 tension of first posthypoxic breath greater than 100 Torr). Brief hypoxia increased VI and decreased end-tidal CO2 tension. In all subjects, termination of hypoxia was followed by a gradual ventilatory decay; hyperoxic VI remained higher than the normoxic baseline for several breaths and, despite the negative chemical stimulus of hyperoxia and hypocapnia, reached a new steady state without an apparent undershoot. We conclude that brief hypoxia is able to activate the afterdischarge mechanism in conscious humans. This contrasts sharply with the ventilatory undershoot that follows relief of sustained hypoxia, thereby suggesting that sustained hypoxia inactivates the afterdischarge mechanism. The present findings are of relevance to the pathogenesis of periodic breathing in a hypoxic environment. Furthermore, brief exposure to hypoxia might be useful for evaluation of the role of afterdischarge in other disorders associated with unstable breathing.

Turtle urinary bladder: regulation of ion transport by dynamic changes in plasma membrane area

Turtle urinary bladder possesses four ion transport processes: Na+ absorption, H+ secretion, and HCO3- secretion-Cl- absorption. Each transport process is performed by a specific epithelial cell type. Granular cells absorb Na+ but they are not sensitive to antidiuretic hormone (ADH), unlike toad bladder granular cells. alpha-Carbonic anhydrase-rich (CA) cells secrete H+ via an apical H+-adenosinetriphosphatase (ATPase). Under conditions of low CO2 tension, this active pump is contained in the limiting membranes of certain cytoplasmic vesicles. The vesicles fuse with the apical membrane, and H+ pumps are incorporated into that membrane, as physiological conditions demand increased H+ secretion. The stimulus for fusion of these vesicles with the apical membrane appears to be intracellular acidification. beta-CA cells secrete HCO3- and reabsorb Cl-, both processes driven by H+-ATPase in the basolateral membrane in series with an apical Cl- -HCO3- exchanger. Increased intracellular adenosine 3',5'-cyclic monophosphate concentration in beta-cells stimulates net HCO3- secretion and induces an electrogenic component of this flux by activating an apical Cl- channel. This activation accompanies the fusion of an intracellular tubulovesicular network with the apical membrane. The membrane of this network may contain Cl- channels.

Effects of hypoxia and hypocapnia on brain redox balance in ducks

Low arterial CO2 tension (PaCO2) experienced by birds during high-altitude flight may result in cerebral vasoconstriction with reduced cerebral O2 delivery. To test this, brain redox balance and blood volume were studied during severe hypocapnia (PaCO2 11-20 mmHg) in ducks. Cerebrocortical redox balance, measured as relative [NADH], and blood volume were measured simultaneously with a fiber-optic fluorometer-reflectometer. Cerebrocortical blood volume (an index of blood flow) fell nearly linearly with PaCO2 during severe hypocapnia, even during severe hypoxemia. Cerebrocortical redox balance was shifted toward reduction of NADH ([NADH] increased) by both hypoxemia and hypocapnia. If hypocapnia causes similar changes in brain blood flow during high-altitude flight, tissue hypoxia will be exacerbated. Tolerance of brain tissue hypoxia during flight may be an important adaptation in high-flying birds.

Correlation between genioglossal and diaphragmatic responses to hypercapnia during sleep.

Oropharyngeal patency during sleep is dependent on the dilating force of the genioglossus, the main tongue protrusor muscle. We measured the ventilatory (Vl), diaphragmatic (EMGdi), and genioglossal (EMGgg) electromyographic responses to CO2 in awake and sleeping goats; delta Vl/delta PETCO2 decreased from awake (0.85 +/- 0.087 L/min/mm Hg) to NREM sleep (0.69 +/- 0.069) to REM sleep (0.57 +/- 0.078, p less than 0.005 versus awake). There were minimal decreases in delta EMGdi/delta PETCO2 and EMGdi at a PETCO2 of 55 mm Hg from awake to NREM, but a significant decrease in EMGdi at a PETCO2 of 55 mm Hg during REM sleep (p less than 0.025 versus NREM). Inspiratory EMGgg was only present above a PCO2 threshold, which was similar for each state (49.3 +/- 2.3 mm Hg PETCO2 awake, 48.8 +/- 2.4 during NREM, 49.5 +/- 2.5 during REM), and delta EMGgg/delta PETCO2 tended to be less during both sleep states compared with that while awake (p = 0.10). At any PCO2, inspiratory EMGgg was markedly inhibited during REM sleep when rapid eye movements were present (phasic REM). We conclude that there is disproportionate inhibition of the genioglossus relative to the diaphragm at low CO2 tensions and at any PCO2 during phasic REM sleep. This imbalance may predispose the upper airway to inspiratory occlusion during sleep.

Alpha and beta types of carbonic anhydrase-rich cells in turtle bladder.

The carbonic anhydrase-rich (CA) cell population of the turtle urinary bladder, which is responsible for the secretion of H+ and probably of HCO-3, was studied by freeze-fracture and thin-section electron microscopy. The apical membrane of the major CA cell type (alpha type) was characterized by microplicae and by a coat of studs on its cytoplasmic side; on freeze-fracture, it contained a dense population of rod-shaped intra-membrane particles. When fixed at low CO2 tension, the apical membrane area of the alpha cell was reduced; its surface displayed microplicae as well as microvilli, and the apical cytoplasm contained many vesicles with rod-shaped particles and studs. The apical membrane of the other (beta type) CA cell was characterized by numerous individual microvilli without microplicae and by a relative absence of rod-shaped particles and studs. Instead, the beta cell contained studs and rod-shaped particles in its basolateral membrane. The ultrastructure and frequency of the beta CA cell were not affected by changes in CO2 tension. We suggest that the alpha cell is responsible for H+ secretion. The reversal of the polarity of the membrane elements in the beta cell and failure to respond to CO2 with amplification of its apical membrane are consistent with a role in HCO-3 secretion.

Effects of light quality, CO2 tensions and NO 3 +? concentrations on the inorganic nitrogen metabolism of Chlamydomonas reinhardii

The blue light dependent utilization of nitrate by green algae under common air and high irradiances, besides its assimilatory nature, is associated with the release of NO2 (-) and NH4 (+) to the culture medium. If the CO2 content of the sparging air was increased up to 2%, previously excreted NO2 (-) and NH4 (+) were rapidly assimilated. When under air and high irradiances the cell density in the culture reached values corresponding to 25 μg Ch 1.ml(-1), no further growth was observed and the highest values of NO3 (-) consumption and NO2 (-) and NH4 (+) release were attained. Besides low CO2 tensions, increasing NO3 (-) concentrations in the medium stimulated the release of NO3 (-) and NH4 (+). Under CO2-free air the consumption of NO3 (-) and the release of NO2 (-) and NH4 (+) on a total N bases were almost stoichiometric and their rates saturated at much lower irradiances than under air. Under CO2-free air high rates of NO2 (-) release were only observed under the blue radiations that were effectively absorbed by photosynthetically active pigments, i.e. 460 nm, but not under 404 and 630 nm radiations. However, the simultaneous illumination of the cells with 404 and 630 nm monochromatic light showed a remarkable synergistic effect on NO2 (-) release.The results are discussed in terms of the close relationship between C and N metabolism, the photosynthetic reducing power required to convert NO inf3 (sup±) -N into R - NH2-N and the blue light activation of nitrate reductase.

Ventilatory response in patients with acute lactic acidosis.

The ventilatory response in acute lactic acidosis was assessed in 39 patients. In 18 patients, the acidosis was associated with phenformin ingestion and in 21, with other causes such as shock and sepsis, but not pulmonary edema. Arterial blood CO2 tensions and plasma bicarbonate concentrations were compared to those previously found in patients with uncomplicated diabetic ketoacidosis. In most of the lactic acidosis patients, arterial blood CO2 fell within the 95% confidence band calculated from the data in the ketoacidotic patients. Only 1 lactic acidotic patient had a triflingly lower CO2 tension. Shock was present in 8 of the 9 lactic acidotic patients whose CO2 tensions were more than 2 torr above the 95% confidence band.

Conductance of Water Vapor in Eggs of Burrowing and Nonburrowing Birds: Implications for Embryonic Gas Exchange

The physical dimensions, water vapor conductance ($G_{H2O}$), permeability (Pm), and effective pore area (Ap) of eggs from a tunnel nester, the bank swallow (Riparia riparia), and an open nester, the barn swallow (Hirundo rustica), were compared. Development of a chorioallantois (CA) was found to increase by as much as 100% the magnitude of $G_{H2O}$, Pm, and Ap in both species. Bank swallow eggs without a CA present have a higher $G_{H2O}$, Ap, and Pm than barn swallows. This greater conductance of bank swallow eggs would not only facilitate water loss in the humid burrow microenvironment but would also enhance CO₂ loss and O₂ uptake through the shell. An improved ability to exchange gases would be advantageous for the eggs of these fossorial nesting birds since they are also exposed to low O₂ and high CO₂ tensions within burrows. A simple steady state model shows that the eggs of bank swallows may be exposed to a gaseous environment as extreme as 17% ;O₂ and 3% CO₂ and still have the same air-cell gas t...

The effect of cyanide and some other carbonyl binding reagents on glycolate excretion by Chlorella vulgaris

The excretion of glycolate by illuminated Chlorella vulgaris cells at low CO2 tension can be stimulated about tenfold by substituting O2 for air, or by addition of cyanide, hydroxylamine, hydrazine or semicarbazide to the cells in air. For each reagent there is a concentration range giving a maximum effect. It is proposed, as a working hypothesis, that the HCN formed internally when the cells are illuminated in O2, may cause the glycolate excretion.

ACETATE METABOLISM BY WHOLE CELLS OF PHAEODACTYLUM TRICORNUTUM BOHLIN12

SUMMARYBoth morphological forms of Phaeodactylum tricornutum incorporated acetate in the light and in darkness. In the dark, the majority of the acetate was oxidized, probably by the tricarboxylic acid cycle. Although some CO2 was formed from acetate in the light, most acetate carbon was found in the cellular lipids. Acetate incorporation in the light was probably a result of both direct and indirect assimilation. The organism grew poorly on acetate in the light at a very low CO2 tension.

The influence of hypocapnia upon intracellular pH and upon some carbohydrate substrates, amino acids and organic phosphates in the brain.

Abstract— In order to evaluate the influence of hypocapnia upon the energy metabolism of the brain, lightly anaesthetized rats were hyperventilated to arterial CO2 tensions of 26, 15 and 10 mm Hg respectively, with subsequent measurements of intracellular pH and of tissue concentrations of carbohydrate substrates, amino acids and organic phosphates. At Pco1= 26 there was a moderate increase in the intracellular pH but when the Pco2 was reduced further to 10 mm Hg the intracellular pH returned to normal, or slightly subnormal, values. The reduction in PCo2 was accompanied by increased cerebral cortical concentrations of lactate, pyruvate, citrate, α‐ketoglutarate, malate and glutamate and by decreased aspartate concentrations. It is concluded that the accumulation of metabolic acids explains the normal value for intracellular pH at very low CO2 tensions. Previous results obtained in man indicate that there is an increased anaerobic production of lactic acid in the brain in extreme hypocapnia. At comparable CO2 tensions the present results showed a small fall in phosphocreatine and a small rise in ADP. However, since the ammonia concentrations were normal or decreased and since there was an increase in citrate, the results give no direct support to the hypothesis of an activation of phosphofructokinase. Since the cerebral venous Po2 was reduced to 20 mm Hg at an arterial CO2 tension of 10 mm Hg the accumulation of acids was probably secondary to tissue hypoxia. However, since there was no, or only a very small, increase in the calculated cytoplasmic NADH/NAD+ ratio, it appears less likely that acids accumulated due to lack of NAD+.

Normalizing Low Arterial CO2 Tension During Mechanical Ventilation

In ten patients with progressive pulmonary consolidation (PPC) during controlled mechanical ventilation with or without positive end expiratory pressure (PEEP) and in five patients with decompensated chronic obstructive lung disease (COLD) during patient triggered assisted respiration, low PaCO 2 was normalized by adding 1 percent to 3 percent CO 2 to the inhaled gas or by adding 200 to 300 milliliters of mechanical dead space to the ventilator tubing. As low arterial P co 2 and high pH were normalized, significant increases occurred in arterial P o 2 , cardiac output and arterial O 2 transport, while both O 2 utilization coefficient and systemic vascular resistance (SYR) decreased. Venous admixture ( Q ˙ s / Q ˙ T ) increased in seven of ten patients and decreased in three of ten with PPC. This variable decreased in the three COLD patients in whom it was measured. The total amount of blood flowing through ventilated areas of the lungs ( Q ˙ T − Q ˙ S ) increased in all patients. The venous O 2 content also increased in all and thereby shunted less desaturated blood to the arterial side. The beneficial circulatory effects of normalizing low Pa co 2 values in part offset the circulatory depressant effects of PEEP. The increase in Pa o 2 resulting from normalizing Pa co 2 allowed lowering of inspired O 2 concentrations from toxic to nontoxic levels even when this was not possible with PEEP alone. Controlling Pa co 2 by regulating FI co 2 during controlled and assisted ventilation with use of a prototype CO 2 mixer (attached to a commercially available air-O 2 mixer) seems more predictable and easier to adjust than the use of mechanical dead space.

Comparative studies of the cytologic and metabolic characteristics of C3H mouse cells during "spontaneous" alteration and neoplastic conversion in vitro.

During long‐term cultivation in vitro animal cells frequently undergo a number of morphological changes which are accompanied by the development of a capacity for continuous growth. This so‐called phase of alteration is sometimes followed by a phase during which the altered cells apparently spontaneously develop tumorogenic properties. It is a matter of discussion whether the difference between these two phases of development is merely a difference of transplantability, or whether more fundamental changes of the altered cells are required before they become tumorogenic. In order to elucidate this problem the cytologic, metabolic, and growth characteristics of C3H mouse cells undergoing “spontaneous” alteration and neoplastic conversion in vitro were investigated. Quantitative studies of cell dimensions, number of nuclei and nucleoli, percentage of mitotic abnormalities and of chromosomal abnormalities revealed no characteristic differences between altered, non‐tumorogenic cells and tumorogenic cells. The most striking cytogenic abnormality was the appearance of an unusually large number of biarmed chromosomes in one of the non‐tumorogenic cell lines (C3H‐M), which showed an accrocentric mode af 36, a subtelo‐centric mode of 3, and a metacentric mode of 26. This abnormality persisted after the development of tumorogenic properties. Although the rate of glycolysis could not be correlated with the rate of tumorogenicity, when four different cell lines were compared, the development and increase of tumorogenic properties within two individual cell lines was accompanied by an increase in the glycolytic capacity. The glycolytic activity did not correlate with the rate of growth as measured by the doubling time under standard conditions of cultivation. However, if pCO2 was raised to 10 per cent atm only cells with a high rate of glycolyis were able to maintain their normal rate of growth. It is suggested 1) that an increased glycolytic capacity may be necessary to maintain a high growth potential of the cells under in vivo conditions, where they might be exposed to low O2 and high CO2 tensions — 2) and that a high growth potential may be essential for tumour production if, as in the case of the present experiments, immunological barriers have to be overcome when the malignancy of the cultured cells is tested in transplantation experiments.

Photoperiod control of diapause in Daphnia. IV. Light and CO2-sensitive phases within the cycle of activation.

The diapaused embryo of the cladoceran, Daphnia pulex, may require light for terminating the diapause, and a single photocycle may be adequate. In D. pulex the light-refractory phase of diapause may be broken or completed in a variety of environments. In the Supply House strain employed in these studies, the usual low temperature treatment is unnecessary when the embryos are placed in constant darkness in sealed containers. Alternatively, the refractory state in constant darkness may be broken with low 02 and high CO2 tensions. Both modifications were shown to be necessary and in that sequence.A single long-day light signal may terminate the diapause when the embryo passes from the photo-refractory to the photo-sensitive phase. Three kinds of light responses were observed, however. Each relates to the treatment given the embryos prior to light exposure.In one so called internal state the embryo requires one long day or two pulses of light. Scant evidence suggests that the first pulse may be interpreted as either dawn or sunset. In this state there are obviously two photo-inductive phases in each inductive cycle. The embryo may change, however, by "losing" one of the photo-inductive phases. In this condition a single two-hour pulse of light, if given at the appropriate time of a thermocycle, may terminate the diapause.A third internal state is introduced when CO2 is employed to break the refractory phase of diapause. The diapause is terminated by a single two-hour pulse of light, and the embryo is continuously sensitive to the light stimulus. However, the pattern of hatching indicates that activation may occur at restricted phases within the induction cycle.Several roles of CO2 may be deduced from the experimental results. An elevated CO2 tension breaks photo-refractoriness. It also induces a "dark" reaction which may need to be completed before the light may stimulate termination of the diapause. Withdrawal of CO2 after 10 hours prevents activation unless a second light pulse is given immediately thereafter. The apparent deferral of light stimulation suggests a third function of CO2, that of "storing" the light signal until the embryo becomes photo-inductive.The potential roles of CO2 are described in a model of photoperiodism that requires photo-induction at two phases in each daily cycle.

The regulation of extra- and intracellular acid-base parameters in the rat brain during hyper- and hypocapnia.

AbstractThe influence of hyper‐ and hypocapnia upon extra‐ and intracellular acid‐base parameters in the brain was studied in rats anaesthetized with nitrous oxide. The arterial CO2 tension was held constant at various values between 12 and 90 mm Hg for 45 min. Assuming a 12 per cent extracellular volume, the intracellular buffer capacity (β= d log Pco2/d pH) could be calculated to 2.27, the intracellular bicarbonate concentration to 14.3 meq/kg of cell water and the equivalent intracellular pH to 7.10 at a tissue C02 tension of 40 mm Hg. Between the tissue Pco2 levels of 20 to 90 mm Hg the CSF bicarbonate varied by 19.5 meq/kg while the corresponding change in the intracellular bicarbonate concentration could be calculated to 12 meq/kg of intracellular water. The calculated buffer capacity of the CSF and intracellular phases greatly exceeded that of arterial blood in vivo. However, the buffering was not constant at different CO2 tensions but increased at low C02 tensions to approach infinite buffering power at extreme hyperventilation. The varying buffer capacity indicates that pH in the extra‐ and intracellular spaces of the brain is regulated not only by physicochemical buffering but also by metabolic mechanisms. The results strongly suggest that the metabolic control is partly exerted by variations in the lactic acid production since the progressive increase in the calculated buffer capacity at low CO2 tensions was parallelled by a continuously increasing lactate concentration, and since the constant buffer capacity at CO2 tensions exceeding 50 mm Hg was associated with lactate concentrations which hardly varied at all.

Modified Atmosphere Storage of Danish Cabbage

Abstract Danish cabbage was stored for several years from late November until April at 0°C and in various combinations CO2, O2 and N2. The best combinations of gas mixtures ranged between 21/2 to 5% of O2 and CO2 with N2 making up the remainder. These combinations reduced weight loss due to respiration and also trimming loss. In atmospheres of low O2 and CO2 tension, heads retained their green color, were succulent and firm, and remained dormant longer. Very low O2 and CO2 treatments had a sweeter taste than normal cabbage, while treatments with slightly higher CO2 had more pungent tastes characteristic of fresh cabbage. Treatments with 71/2% O2 and air checks were bland in taste. Color data were recorded by Hunterlab Color Difference Meter.