O2 Sensitivity Research Articles

Mutants of Azotobacter chroococcum Defective in Hydrogenase Activity

Three classes of Hup‒ mutants of Azotobacter chroococcum were obtained by N-methyl-N′-nitro-N-nitrosoguanidine mutagenesis and screening by H3H uptake: (1) those with no discernible H2-uptake or H2-evolving activity, (2) those showing no uptake but some H2 production and (3) those leaky for both activities. One mutant strain, MCD-124, expressed hydrogenase activity similar to the solubilized wild-type enzyme in O2 sensitivity, sedimenting behaviour and pH optimum. All the other mutants were probably mutated in the hydrogenase structural or processing (methylene blue) genes rather than in genes for hydrogenase-linked respiratory proteins. Four mutants chosen from the first category were complemented for hydrogenase activity by conjugation with Escherichia coli carrying plasmid pHU1 containing Rhizobium japonicum hydrogenase genes. A pHU1 transconjugant of strain MCD-124, on the other hand, did not express any additional hydrogenase activity.

A target-radical hypothesis of radiation damage fixation and modification in oxygenated and hypoxic cells

Radicals in radiation target molecules (presumed to be DNA), are produced by ionizing radiation in at least two ways: Solute and solvent radicals R’ react with target molecules, or ionizations in target molecules become radicals. T’. An intracellular radiation-chemical reaction scheme is therefore proposed in which solute and solvent radicals react with non-target molecules S. (scavengers) or with target molecules (DNA) to produce target radicals. The probability of target radical production is affected by scavenger molecules, and the probability of target radical decomposition to become “uncommitted damage” that the cell may repair is affected by the concentrations of 02, thiols and electronaff,nic sensitizers. which compete with one another to form target-radical products TO:, T&, and TL. This uncommitted damage is then subject to biochemical modification by the cell. The modification results in either “fixation” into F,T02 or F,TL (molecular lesions that are permanent) or enzymatic “repair” through T T’+L-TL:andT+&-T.$, which produce uncommitted chemical damage. Experimental data on strand-break induction in glutathioneproficient and -deficient cells. the inactivation of cells and the computer simulations generally agree that RSH molecules act as scavengers of solvent and solute radicals (R’) in an Ol-independent manner and react with target radicals to reverse T in competition with O2 and/or electronaffinic sensitizers It is postulated that the two categories of uncommitted target lesions TO2 and TL are preferentially repaired by different pathways. Evidence favoring this notion is available in existing literature. Reported values of dose-modification factors when DNA strandbreakage (uncommitted damage) and ceil survival (fixed, unrepaired damage) are the end-points and cells are treated with 02, SH compounds, SH depletion. or electronafTinic sensitizers are compared with calculated values to evaluate the plausibility of the proposed reaction scheme.

Evidence for boundary layer effects influencing the sensitivity of microencapsulated O2 fluorescence indicator molecules.

As Kautsky and Hirsch (1935) and later also Vaughan and Weber (1970) have shown fluorescence quenching by molecular oxygen is often a diffusion-controlled collisional process. Thus, it is not surprising that the oxygen solubility coefficient, and the oxygen diffusion coefficient D of various solvents are of great importance with regard to the O2 sensitivity of the indicator molecules. Fig. 1 shows this effect on different calibration curves for the indicator pyrenebutyric acid dissolved in alkaline water and dioctylphthalate and embedded in a silicone membrane. Calibration has been performed by means of the so-called “Po2 optode”, a schematic drawing of which is shown in Fig. 2 (Lubbers and Opitz, 1975a, b; Opitz and Lubbers, 1976). This optical device incorporates a thin indicator film (1–5 um) between a radiation permeable quartz window and a membrane which separates the fluorescence probes from the medium to be measured (i.e., different partial oxygen pressures in N2-O2 gas mixtures).

The effect of triacontanol on growth, photosynthesis and photorespiration in Chlamydomonas reinhardtii and Anacystis nidulans

Chlamydomonas reinhardtii Dangerad 11–32(90) (−), which exhibits C3 properties, and Anacystis nidulans (Strain no. UTEX 625), which exhibits C4 properties, were used to study the effects of triacontanol on growth, photosynthesis and photorespiration. Photosynthetic rate was measured as CO2 uptake and the O2 inhibition of photosynthesis was used as a measure of photorespiration. Triacontanol dissolved in chloroform and dispersed in Tween‐20 and triacontanol colloidally dispersed in an aqueous solution of sodium tallow alkyl sulfate were tested. Chlamydomonas cultures increased significantly in cell number after 4 days, and in chlorophyll content after 3 days of treatment with 2.3 × 10−8 M TRIA in chloroform/Tween‐20. In cultures of Anacystis the chlorophyll content became significantly higher 3 days after treatment with 2.3 × 10−9 M TRIA and the cell number was noticeably higher than the controls.CO2 uptake by triacontanol‐treated Chlamydomonas cultures was about the same in both 2 and 21% O2, and the O2 inhibition was significantly reduced as compared with the controls. Photosynthesis in Anacystis was O2‐insensitive under the experimental condition used. When Anacystis was treated with triacontanol there was no change in the rate of CO2 uptake and no change in the O2 sensitivity of its CO2 uptake. It appears that triacontanol affects some process which regulated the balance between photosynthesis and photorespiration, but other processes which result in increased growth are probably also affected.

A combined transcutaneous PO2-PCO2 electrode with electrochemical HCO3- stabilization.

Combined transcutaneous PO2-PCO2 electrodes are described in which the interaction between the two electrodes due to OH- production at the O2 cathode has been eliminated. An anode of either anodized aluminum or platinum has been driven at a current equal to cathode current to force stoichiometric consumption of OH- at its rate of production. The AgCl reference electrode operates at zero current. O2 sensitivity was not significantly altered by electrolyte pH variation from 6.7 to 9.0 with variations by PCO2. These electrodes have been found stable both with and without spacers, and with electrolytes dissolved in 50-100% ethylene glycol. In 22 anesthetized patients, with electrode temperature of 43 degrees C (s refers to skin surface, a to arterial blood); PsO2 = 0.52PaO2 + 15 (range 54-300) (r = 0.66; Sy . x = 29.6; n = 46); and PsCO2 = 1.39PaCO2 + 2.1 (range 24-98) (r = 0.99; Sy . x = 2.28; n = 48).

In vivo reduction of cyclopropane by Azotobacter vinelandii nitrogenase

NITROGENASE from N2-fixing aerobes such as Azotobacter vinelandii is stable to air in crude extracts but on fractionation into its two protein components, Fe–Mo protein and Fe protein it manifests the O2 sensitivity characteristic of other nitrogenases1. This difference between the air-stable and air-labile forms of the enzyme has been ascribed to various causes2–4. More generally, the incompletely defined correlations between in vivo and in vitro nitrogenase function with respect to optimal component ratio5, local pH6, ATP stoichiometry7, reductant8, catalytic behaviour4,9 and other important enzymatic parameters are a source of ambiguity in biochemical studies on the cell-free enzyme. In principle, effects from changes in many of these parameters can be studied by parallel in vivo and in vitro substrate reduction and inhibition studies. In practice10, restrictive limitations are imposed by the paucity of nitrogenase substrates that are at once (1) well bound, (2) capable of diagnostically complex chemical interactions, and (3) compatible with function of the enzyme in living microorganisms. For example, among known substrates other than N2 itself, C2H2 is deficient in reduction complexity10, HCN is excluded by its cytotoxicity and acrylonitrile, which displays interesting product patterns11, is a poor substrate12. Recently, cyclopropene was shown to undergo ATP-dependent nitrogenase-catalysed reduction to propene and cyclopropane in vitro13. The product ratio of ∼2:1 alkene:cycloalkane was found to be insensitive to purification over a specific activity range of 40–1,200 in conventional assay conditions. We report here results of further nitrogenase-cyclopropene investigations which establish that: (1) nitrogenase in living A. vinelandii catalyses cyclopropene reduction to the products observed in vitro in the same ∼2:1 ratio; the Km for formation of either product is very similar if not identical to that obtained with cell-free enzyme; (2) with purified components (specific activity up to 2,000) at optimal stoichiometry, the Km for formation of the reduction products (propene and cyclopropane) is 0.01 atm, corresponding to a molar Km as low as that of N2 (and C2H2). These findings strengthen the case for catalytic similarity between in vivo and in vitro nitrogenase. Conversely, they substantiate the importance of cyclopropene product ratio as a chemical probe for the enzyme and as an important new criterion for nitrogenase biomimetic chemistry.

The Use of Concentrated NaN03in tcPo2Electrodes to Diminish O2Consumption and Dehydration Drift

We investigated: (1) The effects of NaN03 concentration, membrane material and thickness, and electrolyte layer thickness on electrode O2 consumption, stirring effect (O) and response time; (2) The effect of NaNO3 on P(H20) and electrode drift; and (3) The effect of KCl on Ag deposition at the cathode. Electrolytes containing 0–8 m NaN03, 0.01 m KCl, and 0.1 m pH 7 phosphate were tested in a 20 μ cathode tcPo2 electrode at 42dC. Increasing NaNO3 concentration reduced O2 solubility and sensitivity by a factor: e-(C/4.6). Thus, sensitivity was a linear function of solubility. Without cellophane, sensitivity with 12 μm polypropylene was 50% that of 25 μm Teflon; 7 m NaNO3 reduced sensitivity for both membranes by about 60%. 12 μ cellophane, by increasing the thickness of the electrolyte layer, minimized the difference between the membranes and exaggerated the effects of increasing NaNO3 concentration on sensitivity. O was a linear function of sensitivity. Cellophane decreased the ratio of O to sensitivity. Response times of electrodes were almost unaffected by addition of NaNO3, but were increased as expected by use of thicker membranes, and by addition of cellophane spacers. Electrolyte vapour pressure was decreased 67% by addition of 7 m NaNO3. When electrolyte vapour pressure differed significantly from that of skin or calibration solutions, water crossed the polypropylene or Teflon membranes, changing the O2 sensitivity, and causing drift both on skin and in calibration solutions. With KCl containing electrolytes, silver deposition occurs at the cathode, the rate of deposition increasing greatly as KCl concentration approaches saturation. Thus addition of NaNCO3 to O2 electrolytes lowers vapour pressure, delays dehydration, reduces O2 sensitivity by reducing permeability of the electrolyte layer to O2, and thereby reduces the gas/skin correction factor O, without significantly delaying response time, and without increasing silver deposition.

Characteristics of Non-Aqueous Electrolytes for Transcutaneous Oxygen Electrodes

We investigated the characteristics of non-aqueous solvents for tcPO2 electrolytes, using a tcPO2 electrode with three 15 micrometer platinum cathodes set in a polished glass surface, a 17.8 mm2 silver anode covered with a 25 micrometer Telfon membrane, with and without a 12 micrometer cellophane spacer, and polarized at--0.8v. We examined the effect of ethylene glycol (EG) concentration, in water, on O2 sensitivity, stirring effect, in vitro drift, in vitro response time, behaviour on the skin of newborn infants and in vivo response time. We found the following: (1) O2 sensitivity was reduced by increasing EG concentration. (2) phi, the stirring effect (gas/50% glycerine) was 1.01 at 90% EG with cellophane, but higher without cellophane. (3) In vitro drift at 44 degree C electrode temperature, in 43 degree C water (simulating skin), was reduced with 90% EG, 25 micrometer Telfon and no spacer, but increased with a spacer. (4) In vitro response time was increased with EG. (5) Correlations with arterial PO2 in a group of newborns was as excellent with an electrode made with 90% EG and 25 micrometer Telfon, without spacer, as it was with our previous study using aqueous electrolyte and 12 micrometer Telfon wint 12 micrometer cellophane: (tcPO2 = 1.32 + 0.988 PaO2 r = 0.987). In vivo response time was not prolonged. Using EG, the tc PO2 electrode membrane required changing only after 7--9 days, compared with 1--2 days when using aqueous electrolytes. No advantage of using cellophane spacers was identified in these in vivo studies.

CONTINUOUS MONITORING OF ARTERIAL PaCO2 BY NON-INVASIVE TRANSCUTANEOUS METHOD

Antimony oxide (Sb-SbOx) and pH-sensitive glass electrodes, combined with reference electrodes, surrounded by electrolyte and covered with gas permeable membrane (gpm) were used for transcutaneous PCO2(PtcCO2) measurement. A servo-controlled heater unit maintained sensor temp, and produced local hyperemia. A thermistor was placed under the gpm to measure true sensor temp. O2 sensitivity of Sb-SbOx electrode was reduced greatly in the 65-175 mm Hg PO2 range by cell loading, but below 65 mm Hg, O2 sensitivity was significant. The pH-sensitive glass electrode was preferred due to its insensitivity to O2. After the sensor was placed on the skin of rabbits, it was calibrated in situ and its temp, coefficient established. This was repeated at the end of the 6-hr. experiment. For the best correlation between PaCO2 and PtcCO2, the skin surface temp, was maintained between 40-42°C, as lower temps, made ptcCO2 higher. Based on in situ calibration, the fitted regression line had a slope of 1.029, intercept of -4.39, and SE of 4.14 mm Hg PCO2. In the range of 21-75 mm Hg, PtcCO2 was 2.2 - 3.8 mm Hg below PaCO2. Based on in situ calibration with one point PaCO2, calibration, the line had a slope of 1.0, intercept of 0.6, SE of 3.4 mm Hg PCO2, and linear regression coefficient of 1.0. These data indicate the usefulness of PtcCO2 monitoring to indicate PaCO2 changes under normal physiologic conditions.

Effect of Rhizosphere pO2 on Nitrogen Fixation by Excised and Intact Nodulated Soybean Roots1

The N2‐fixing legume nodule has an O2 requirement for ATP production to support nitrogenase (ECI.7.99.2) activity, however, the internal partial pressure of O2 (pO2) in the nodule must be maintained at low level because of the O2 sensitivity of nitrogenase. Effects on N2 fixation of short‐term exposures of the rhizosphere to altered external pO2's using both excised nodulated soybean [Glycine max (L.) Merr.] roots and intact plants were investigated utilizing acetylene (C2‐H2) reduction. Exposures of 30 min to supra‐ambient pO2's of 0.26 to 0.41 atm stimulated N2[C2H2] fixation by excised roots, but not intact plants while short exposures to a sub‐ambient pO2 of 0.05 atm reduced N2[C2H2] fixation by excised roots more than by intact plants. Short exposures of 30 rain to a supra‐optimum pO2 of 0.65 to 0.90 atm reduced N2[C2H2] fixation in both excised roots and intact plants, and in contrast to exposure to other O2 concentrations, there was only partial recovery of N2[C2H2] fixation by the intact plants and a further decline by the excised roots on reincubation in ambient O2. With excised roots, altered pO2 effects were age‐dependent with a decline in the optimum pO2 from 0.41 to 0.26 atm and intensification of the detrimental effects of high pO2. It is concluded that; 1) the excised root is more sensitive to altered pO2 than intact plants, 2) measurements of the effects of stress, such as altered pO2, on N2 fixation should be made on intact plants, and 3) ambient pO2 is not limiting for N2 fixation but short‐term exposures to sub‐ambient pO2 will limit N2 fixation.

Coronary intercapillary distance during growth: relation to PtO2 and aerobic capacity.

Intercapillary distance (ICD) was measured in left ventricles of rats beating in situ. Between 40 and 400 days of age, left ventricular weight increased threefold and ICD increased from 12.5-19.5 mum. ICD could be decreased by at least 2 mum at all ages studied. The number of capillaries which must be recruited to reduce ICD by 2 mum fell from 1,200/mm2 at 40 days to 280/mm2 at 400 days. Ventricular growth did not affect the O2 sensitivity of precapillary sphincters or the uniformity of capillary spacing. Calculations indicate that under basal conditions tissue PO2 (Pto2) in subepicardium is about the same at 40 and 400 days, even though VO2 per gram, capillary density, and ICD change twofold, twofold, and 7 mum, respectively. Nevertheless, as the ventricle grows, capillary recruitment becomes progressively less effective in defending Pto2 under conditions of stress. Diminished coronary capillary compensation for stress may, in part, account for the effect of age on the maximum aerobic capacity of the whole animal.

Adaptation of Nitrogen Fixation by Intact Soybean Nodules to Altered Rhizosphere pO2

The N(2)-fixing legume nodule requires O(2) for ATP production; however, the O(2) sensitivity of nitrogenase dictates a requirement for a low pO(2) inside the nodule. The effects of long term exposures to various pO(2)s on N(2)[C(2)H(2)] fixation were evaluated with intact soybean (Glycine max [L.] Merr., var. Wye) plants. Continuous exposure of their rhizosphere to a pO(2) of 0.06 atmospheres initially reduced nitrogenase activity by 37 to 45% with restoration of original activity in 4 to 24 hours and with no further change in tests up to 95 hours; continuous exposure to 0.02 atmosphere of O(2) initially reduced nitrogenase activity 72%, with only partial recovery by 95 hours. Similar exposures to a pO(2) of 0.32 atmospheres had little effect on N(2)[C(2)H(2)] fixation; a pO(2) of 0.89 atmospheres initially reduced nitrogenase activity by 98% with restoration to only 14 to 24% of that of the ambient O(2) controls by 95 hours. Re-exposure to ambient pO(2) of plants adapted to nonambient pO(2)s reduced N(2)[C(2)H(2)] fixation to similar magnitudes as the reductions which occurred upon initial exposure to variant pO(2) conditions, and a time period was required to readapt to ambient O(2). It is concluded that the N(2)[C(2)H(2)]-fixing system of intact soybean plants is able to adapt to a wide range of external pO(2)s as probably occur in soil. We postulate that this occurs through an undefined mechanism which enables the nodule to maintain an internal pO(2) optimal for nitrogenase activity.

Minimal Dissolved Oxygen Requirements of Aquatic Life with Emphasis on Canadian Species: a Review

This article reviews the sensitivity, responses, response thresholds, and minimum oxygen requirements of marine and freshwater organisms with strong emphasis on Canadian species. The analysis attempts to define low dissolved oxygen thresholds which produce some physiological, behavioral, or other response in different species.Oxygen availability is discussed with reference to seasonal, geographical, or spatial variation in dissolved oxygen. Factors affecting availability of dissolved oxygen include atmospheric exchange, mixing of water masses, upwelling, respiration, photosynthesis, ice cover, and physical factors such as temperature and salinity. Dissolved oxygen terminology is summarized and tables are included for both fresh and saltwater O2 solubility at different temperatures.Incipient O2 response thresholds are used in a statistical analysis to develop oxygen criteria for safeguarding various groups of freshwater and marine fish. These include mixed freshwater fish populations including or excluding salmonids, freshwater salmonid populations, salmonid larvae or mature salmonid eggs, marine anadromous and nonanadromous species. Criteria are based on threshold oxygen levels which influence fish behavior, blood O2 saturation, metabolic rate, swimming ability, viability and normal development of eggs and larvae, growth, circulatory dynamics, ventilation, gaseous exchange, and sensitivity to toxic stresses. The criteria provide three levels of protection for each fish group and are expressed as percentage oxygen saturation for a range of seasonal temperature maxima.Oxygen tolerances and responses of aquatic invertebrates to low oxygen are reviewed for freshwater and marine species according to habitat. No invertebrate criteria are proposed owing to the capacity for many invertebrate species to adopt anaerobic metabolism during low O2 stress. It is suggested that the criteria proposed for fish species will provide a reasonable safeguard to most invertebrate species. It appears likely, however, that a change in oxygen regime to one of increased O2 scarcity will probably influence invertebrate community structure.It is suggested that criteria for protection of aquatic life be implemented by groups of experienced individuals. The group should consider the natural oxygen regime for a specific water body and its natural variability, the aquatic life therein and its value, importance, relative O2 sensitivity, and the possibility of interactions with toxicants and other factors that may compound the stress produced by low O2 on aquatic life. Each water body and its aquatic life should be considered as a unique situation and criteria application should not encompass diverse areas, habitats, or biological associations as if they were identical.

Mitochondrial respiratory chain of carotid body and chemoreceptor response to changes in oxygen tension.

Mitochondrial respiratory chain of carotid body and chemoreceptor response to changes in oxygen tension.

Chemosensitivity in normal subjects, athletes, and patients with chronic airways obstruction

Studies of CO2 and O2 sensitivity have been made using rebreathing methods in normal subjects, athletes, and patients with and without chronic airways obstruction. The rebreathing techniques enabled isoxic CO2 response curves and isocapnic O2 response curves to be constructed from many points obtained over a short time. There was little difference in response among the groups of normal subjects but the patients with lung disease had a flatter CO2 response curve and required lower levels of Po2 to stimulate ventilation. When ventilation was expressed as a fraction of the maximal voluntary ventilation, much of the difference between normal subjects and chest patients disappeared, suggesting that the reduced ventilatory response may be of mechanical origin. There remained some patients who were truly insensitive to one or both stimuli and they appeared to be those whose clinical condition was poorest. rebreathing techniques; isoxic CO2 sensitivity; isocapnic O2 sensitivity; relation to ventilatory capacity; insensitivity of some patients

Ventilatory responses to acute and chronic hypoxia in goats after sinus nerve section.

ArticleVentilatory responses to acute and chronic hypoxia in goats after sinus nerve section.S C Sorensen, and A H MinesS C Sorensen, and A H MinesPublished Online:01 Jun 1970https://doi.org/10.1152/jappl.1970.28.6.832MoreSectionsPDF (845 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByPostnatal changes in O2 and CO2 sensitivity in rodentsRespiratory Physiology & Neurobiology, Vol. 272Comparative Control of RespirationThe rhythmic, transverse medullary slice preparation in respiratory neurobiology: Contributions and caveatsRespiratory Physiology & Neurobiology, Vol. 186, No. 2Neuromodulation: Purinergic Signaling in Respiratory Control1 January 2013Women at altitudeVentilatory Responses to Acute and Chronic Hypoxia1 January 2011Effects of carotid glomectomy on erythron parameters in rats differing in the resistance to acute hypoxiaBulletin of Experimental Biology and Medicine, Vol. 122, No. 1Theophylline and hypoxic ventilatory response in the rat isolated brainstem-spinal cordRespiration Physiology, Vol. 100, No. 1Ventilatory responses to acute and chronic hypoxic hypercapnia in the ground squirrelRespiration Physiology, Vol. 98, No. 2Respiratory Depression following Acute Hypoxia in Vagotomized and Carotid Sinus Nerve Denervated CatsReflex Responses to Chemoreceptor Stimulation1 January 2011Ventilatory Control at High Altitude1 January 2011Role of the carotid bodies in ventilatory acclimation to chronic hypoxia by the awake catRespiration Physiology, Vol. 58, No. 2Role of carotid chemoreflex in respiratory acclimatization to hypoxemia in goat and sheepRespiration Physiology, Vol. 46, No. 3Central chemosensitivity: A respiratory drive21 June 2005Relative contribution of central and peripheral chemoreceptors to the ventilatory response to CO2 during hyperoxiaRespiration Physiology, Vol. 37, No. 3The contribution of the peripheral chemoreceptors to the ventilatory response to CO2 in anaesthetized cats during hyperoxiaRespiration Physiology, Vol. 37, No. 3Evidence for cerebral extracellular fluid [H+] as a stimulus during acclimatization to hypoxiaRespiration Physiology, Vol. 32, No. 2Hydrogen Ion Homeostasis of the Cerebral Extracellular FluidHYPOCHOLESTEROLÆMIC EFFECT OF MILKThe Lancet, Vol. 310, No. 8041HYPERCAPNIA DURING OXYGEN THERAPYThe Lancet, Vol. 310, No. 8041Regulation of RespirationNew England Journal of Medicine, Vol. 297, No. 4Carbon dioxide sensitivity of the central chemosensitive mechanismsPfl�gers Archiv European Journal of Physiology, Vol. 367, No. 3Ventilatory response of goats to transient changes in CO2 and O2 during acute hypoxiaRespiration Physiology, Vol. 24, No. 2Blood and CSF acid-base changes, and rate of ventilatory acclimatization of awake dogs to 3,550 mRespiration Physiology, Vol. 24, No. 2Hypoxia-induced tachypnea in carotid-deafferented catsRespiration Physiology, Vol. 23, No. 1Adaptation to Hypocapnia and its Role in Adaptation to HypoxiaThe Effect of Controlled System (Plant) Dynamics on Ventilatory Responses to Disturbances in CO 2 BalanceIFAC Proceedings Volumes, Vol. 6, No. 4The effect of chronic metabolic acidosis and alkalosis on ventilation during exercise and hypoxiaRespiration Physiology, Vol. 17, No. 3Hyperoxieatmung bei Patienten mit alveolärer HypoventilationPneumonologie Pneumonology, Vol. 149, No. 1Role of the arterial chemoreceptors in ventilatory adaptation to hypoxia of awake dogs and rabbitsRespiration Physiology, Vol. 17, No. 2The influence ofPa O2 on the effects of sinus nerve stimulation with intact and inactivated vagiPfl�gers Archiv European Journal of Physiology, Vol. 341, No. 4The regulation of cerebrospinal fluid pHKidney International, Vol. 1, No. 5The effect of graded hypoxia with and without exercise on ventilatory acclimatizationRespiration Physiology, Vol. 14, No. 3Regulation of respiration in goat and its adaptation to chronic and life-long hypoxiaRespiration Physiology, Vol. 12, No. 3Changes in the Electrochemical Potential Difference for HCO 3 - - between Blood and Cerebrospinal Fluid and in Cerebrospinal Fluid Lactate Concentration during Isocarbic Hypoxia 1Acta Physiologica Scandinavica, Vol. 81, No. 2 More from this issue > Volume 28Issue 6June 1970Pages 832-5 https://doi.org/10.1152/jappl.1970.28.6.832PubMed5427279History Published online 1 June 1970 Published in print 1 June 1970 Metrics

Nitrous oxide as a sensitizer of bacterial spores to x-rays.

SummaryIn N2O-saturated water, spores of Bacillus megaterium exhibit sensitivity to x-rays that is higher than that in N2-saturated water, but lower than that in O2-saturated water. O2-N2O mixtures show O2 sensitivity. Ethyl alcohol present simultaneously at 0·8 Molar prevents the N2O sensitization completely. These results can be interpreted as due to an increase in ·OH radical yield by N2O; and removal of ·OH by ethanol. In dilute solutions of ethanol only partial reversal (or competition) of the N2O effect is observed. This effect is concentration-independent over a wide range of dilute concentrations. An apparent exhaustion of the alcohol is observed at higher doses, producing a two-component survival curve, each component being exponential. The break-points are dose-dependent, with only one being expected on the basis of measured yields in chemical systems; and the slope beyond the break-point is always that of O2-saturated suspensions. The last results can be interpreted as indicating two actions of...

Biochemical patterns of some heterotrophic marine bacteria grown in defined media.

SUMMARY: Three heterotrophic marine bacteria, isolated from the Tyrrhenian sea on the basis of their relative growth requirements for acetate and ammonium, were studied mainly in regard to their biochemical and nutritional characters. Data about the amino acid pools, protein amino acids, CO2: O2 ratios, enzyme activities and sensitivities to metal ions and antibiotics, are reported. The utility of an index obtained from the study of the oxygen uptake with various organic-C concentrations and the use of defined media for a more satisfactory discrimination of the various strains, is shown.