The compression-ordering and solubility-disordering effects of high pressure gases on phospholipid bilayers.

Inert gases at high pressure may compress and dissolve in tissue of intact organism to result in narcosis, reversal of the effects of anesthetic agents or hyperexcitability. The effects of 51 and 102 atm of helium, hydrogen, nitrogen, argon, xenon and nitrous oxide on the molecular motion of nitroxide spin-labeled phospholipid-cholesterol bilayers were measured by electron paramagnetic resonance (EPR) techniques. Immediately, application of high pressures of all gases decreased the molecular motion of the fatty acid chains of the membrane phospholipids; the magnitude of ordering was linearly related to the amount of pressure applied. The second effect was an increase in molecular motion of the fatty acid chains which appeared more slowly due to the slow gas diffusion through the column of lipid dispersion. The magnitude of disorder of the phospholipid membrane at equilibrium correlated with the known lipid solubilities of the gases in olive oil as well as with the anesthetic potency of all the gases except xenon. The environment of the spin label became less polar as the gases diffused into the bilayer. The present studies in the phospholipid model membrane show that the net effects of high pressure gases in the lipid phase consist of an initial ordering of the membrane by compression opposed by the ability of the gas molecules to diffuse and dissolve in the lipid bilayers and disorder them. It is thus suggested that the resultant perturbations of the membrane lipid fluidity by high pressure gases may subsequently be transmitted to membrane-bound protein to result in changes that may be associated, in part, with the diverse effects of anesthesia and of the high pressure nervous syndrome (HPNS) observed in deep-sea divers. The model system may be useful in developing gas mixtures which minimize HPNS.     

The effect of helium and of hydrogen at high pressure on the cell division of Tetrahymena pyriformis W.

The rate of cell division of Tetrahymena growing in an observational high pressure vessel was measured at selected pressures of helium, hydrogen and at high hydrostatic pressure. Pressures greater than 100 atm reduced the rate of division, but the gases inhibited division to a lesser degree than pure hydrostatic pressure. Hydrogen's effect was distinguishable from that of hydrostatic pressure at 130 atm or more, while helium's effect appeared at 175 atm. These inert gases probably counteract the action of pressure by stabilising apolar pressure-labile targets.     

High gas pressure effects on yeast

Dried microorganisms are particularly resistant to high hydrostatic pressure effects. However, exposure to high pressures of nitrogen proved to be effective in inactivating dried yeasts. In this study, we tried to elucidate this mechanism on Saccharomyces cerevisiae. High-pressure treatments were performed using different inert gases at 150 MPa and 25 degrees C with holding time values up to 12 months. The influence of cell hydration was also investigated. For fully hydrated cells, pressurized gases had little specific effect: cell inactivation was mainly due to compression effects. However, dried cells were sensitive to high pressure of gases. In this latter case, two inactivation kinetics were observed. For holding time up to 1 h, the inactivation rate increased to 4 log and was linked to a loss of membrane integrity and the presence of damage on the cell wall. In such case cell inactivation would be due to gas sorption and desorption phenomena which would rupture dried cells during a fast pressure release. Gas sorption would occur in cell lipid phases. For longer holding times, the inactivation rate increased more slightly due to compression effects and/or to a slower gas sorption. Water therefore played a key role in cell sensitivity to fast gas pressure release. Two hypotheses were proposed to explain this phenomenon: the rigidity of vitrified dried cells and the presence of glassy solid phases which would favor intracellular gas expansion. Our results showed that dried microorganisms can be ruptured and inactivated by a fast pressure release with gases.     

Effect of high-pressure gas on yeast growth

Microcalorimetry is a useful tool for monitoring the growth behavior of microorganisms. In this study, microcalorimetry was used to investigate the effects of nitrogen, air, oxygen, nitrous oxide, argon, and krypton at high pressure on the growth of the yeast Saccharomyces cerevisiae. Growth thermograms (metabolic heat vs. incubation time) were generated to estimate metabolic activity under compressed gases and to determine the 50% inhibitory pressure (IP(50)) and minimum inhibitory pressure (MIP), which are regarded as indices of the toxicity of compressed gases. Based on MIP values, the most toxic to the least toxic gases were found to be: O(2) > N(2)O > air > Kr > N(2) > Ar.     

Inhibition of microbiological sulfide oxidation by methanethiol and dimethyl polysulfides at natron-alkaline conditions

To avoid problems related to the discharge of sulfidic spent caustics, a biotechnological process is developed for the treatment of gases containing both hydrogen sulfide and methanethiol. The process operates at natron-alkaline conditions (>1 mol L⁻¹ of sodium- and potassium carbonates and a pH of 8.5–10) to enable the treatment of gases with a high partial CO₂ pressure. In the process, methanethiol reacts with biologically produced sulfur particles to form a complex mixture predominantly consisting of inorganic polysulfides, dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS). The effect of these organic sulfur compounds on the biological oxidation of sulfide to elemental sulfur was studied with natron-alkaliphilic bacteria belonging to the genus Thioalkalivibrio. Biological oxidation rates were reduced by 50% at 0.05 mM methanethiol, while for DMDS and DMTS, this was estimated to occur at 1.5 and 1.0 mM, respectively. The inhibiting effect of methanethiol on biological sulfide oxidation diminished due to its reaction with biologically produced sulfur particles. This reaction increases the feasibility of biotechnological treatment of gases containing both hydrogen sulfide and methanethiol at natron-alkaline conditions.     

Factors determining temporal pattern of isobaric supersaturation

It is possible to produce a transient supersaturation or undersaturation in tissues and blood by sequentially breathing gases with different equilibration rates. If the ambient gas pressure is sufficiently high, the induced supersaturation can produce vascular bubbles. By means of the classical perfusion-dependent model of inert gas elimination, which assumes that the effects of diffusion are minimal, the magnitude of the total inert gas pressure can be predicted. If, however, the effects of diffusion cannot be ignored, the supersaturation could be substantially larger. This paper estimates the effects of diffusion in a Krogh cylinder on the supersaturation produced by suddenly changing the inert gas partial pressure in the blood. The results of these estimates indicate that diffusion plays a role in this transient supersaturation only in long Krogh cylinders with high blood flows. The effects of diffusion are further reduced by the finite time necessary to switch the inert gases in arterial blood. The conclusions are supported by experiments that measure vascular bubble production after a switch of the inert portion of the inspired gas. These experiments further show that the formation of vascular bubbles after such a switch cannot be entirely explained by the different diffusion constants of the gases used.     

The significance of the activity of dissolved oxygen, and other gases, enhanced by high hydrostatic pressure

The partial pressure of oxygen and other gases dissolved in water and subjected to high hydrostatic pressure is increased. Although this was established many years ago it remains a problematical phenomenon. The review deals with some of the underlying theoretical difficulties and discusses the kinetic and environmental implications of the pressure-enhanced partial pressures.     

The opposing physiological effects of high pressures and inert gases.

The physiological effects on mammals of elevated pressures (approximately 100 atmospheres) must be considered in the context of the inert gases breathed. The most striking effect of pressure per se is a central hyperexcitability manifest at first by trembling of the entremities and finally by convulsions. Paralysis and death occur at higher pressures. The primary effects of the inert gases breathed are inert gas narcosis and general anesthesia. The exciting effects of pressure per se and the depressive effects of the inert gases tend to oppose each other. Thus consciousness may be restored to anesthetized mice by raising the pressure, and conversely the threshold pressure that causes convulsions is elevated in the presence of anesthetics. These mutually antagonistic effects can be rationalized in terms of model which proposes that both anesthetics and pressure non-specifically perturb thelipid bilayer regions of neutral membranes. This model is termed the critical volume hypothesis. Anthesthetics dissolve in and expand these lipid bilayer regions, while pressure causes mechanical compression. Expansion leads to anesthesia and compression to convulsions if a critical degree of change is achieved. At elevated partial pressures of inert gas the gas-induced expansion is opposed by the compression of pressure per se. With very insoluble gases, such as helium, this expansion is so small that net compression results and the effects of helium differ little from those of pressure per se. With more soluble gases, such as nitrogen, net expansion results in inert gas narcosis and anesthesia. The critical volume hypothesis enables "safe" mixtures of "expanding" and "compressing" gases to be defined. These enable higher pressures to be better tolerated by mammals.     

Opposing effects of anesthetics on pressure tolerance and compression rate effect

Inert gas narcotics increase intrinsic pressure tolerance (1,000Pc) in CD-1 mice but interfere with development of the protective responses raising seizure thresholds during slower compression (e.g., 60Pc). This secondary narcotic effect can block up to 40% of the total attainable increase in Pc. The narcosis susceptible moiety of this compression rate effect develops early, whereas a narcosis resistant remnant accounts for increase in Pc occurring after 90 min of compression or pressure exposure. Pressure conditioning by multiday pressure exposure entails increases in both 60Pc and 1,000Pc and in virtual annullment of the compression rate effect. The effect can be completely blocked by narcotic gases in the conditioning atmosphere. In addition to blocking part of the compression rate effect the presence of narcotic gases under these conditions can reverse the effects of previously established pressure conditioning. 60Pc regresses much more slowly under these conditions than 1,000Pc. Either reversal rate is much more rapid in air at 1 ATA than at 80 ATA under 0.9 atm N2O. The implications of these data are discussed with regard to evaluation of the hypothesis of antagonism between inert gas narcotics and high pressures and to elaboration of the monoamine hypothesis to account for the modification of the compression rate effect by narcotic gases.     

Effects of hydrostatic pressure and inert gases on platelet aggregation in vitro

A novel cuvette was used to subject citrated platelet-rich plasma (PRP) to high hydrostatic pressure with negligible contamination by He (used for compression of the apparatus). Aggregation was induced at pressure by ADP and quantified turbidimetrically. The maximum degree of aggregation (MDA) was reduced from a control level of 82.2 to 53.6% by exposure to 101 ATA. Because decompression bubbles did not form, aggregation was also measured immediately after a compression cycle. After exposure to 101 ATA hydrostatic pressure, platelets responded normally to ADP at 1 ATA. In a matching apparatus, PRP was equilibrated with high partial pressures of inert gases. Normal physiological plasma Po2 and pH were maintained during equilibration. N2O (5 ATA) reduced the MDA from 86.5 (control) to 58.1%. N2 (51 ATA) reduced the MDA from 74.7 (control) to 51.6%, and 101 ATA Pn2 reduced the MDA from 78.0 (control) to 32.3%. He (100 ATA) reduced the MDA from 83.6 to 38.6%. It was concluded that platelet aggregation was relatively sensitive to hydrostatic pressure and less sensitive to inert gases than predicted from their anesthetic potency ratios.     

Dissolved atmospheric gas in xylem sap measured with membrane inlet mass spectrometry

A new method is described for measuring dissolved gas concentrations in small volumes of xylem sap using membrane inlet mass spectrometry. The technique can be used to determine concentrations of atmospheric gases, such as argon, as reported here, or for any dissolved gases and their isotopes for a variety of applications, such as rapid detection of trace gases from groundwater only hours after they were taken up by trees and rooting depth estimation. Atmospheric gas content in xylem sap directly affects the conditions and mechanisms that allow for gas removal from xylem embolisms, because gas can dissolve into saturated or supersaturated sap only under gas pressure that is above atmospheric pressure. The method was tested for red trumpet vine, Distictis buccinatoria (Bignoniaceae), by measuring atmospheric gas concentrations in sap collected at times of minimum and maximum daily temperature and during temperature increase and decline. Mean argon concentration in xylem sap did not differ significantly from saturation levels for the temperature and pressure conditions at any time of collection, but more than 40% of all samples were supersaturated, especially during the warm parts of day. There was no significant diurnal pattern, due to high variability between samples.     

Effects of compressed hydrocarbon gases on the growth activity of Saccharomyces cerevisiae

The inhibitory action of compressed hydrocarbon gases on the growth of the yeast Saccharomyces cerevisiae was investigated quantitatively by microcalorimetry. Both the 50% inhibitory pressure (IP(50)) and the minimum inhibitory pressure (MIP), which are regarded as indices of the toxicity of hydrocarbon gases, were determined from growth thermograms. Based on these values, the inhibitory potency of the hydrocarbon gases increased in the order methane < ethane < propane < i-butane < n-butane. The toxicity of these hydrocarbon gases correlated to their hydrophobicity, suggesting that hydrocarbon gases interact with some hydrophobic regions of the cell membrane. In support of this, we found that UV absorbing materials at 260 nm were released from yeast cells exposed to compressed hydrocarbon gases. Additionally, scanning electron microscopy indicated that morphological changes occurred in these cells.     

Portable Device for Preparation and Delivery of Gas Mixtures

A simple, portable device for the preparation and delivery of gas mixtures has been designed and constructed. The basic feature of the device is the use of gas flow controllers to maintain stable flow rates over a wide range of downstream pressures, instead of the capillary tubes and water-filled barostats commonly used in gas-mixing devices. Elimination of the barostat avoids problems such as water leakage, the loss of gases through the barostat, and changes in gas pressure due to evaporative loss of water from the barostat. The absence of a barostat also provides a closed system, allowing the use of the device for mixing and delivering of toxic gases. The prototype of the device has been used to prepare mixtures of different gases for more than 1 year and has been found to operate consistently and reproducibly. The actual concentrations of O₂, CO₂, and N₂ in gas mixtures (determined by gas chromatography) immediately after mixing were between 2.2 and 6.6% of the desired values in four performance tests. Fluctuations in concentration of gases in mixtures after 9 days of continuous gas delivery was less than 2% in four performance tests.     

Structural and physiological differences between montane and lowland avian eggs and embryos

A few avian species breed at altitudes up to 6500 m. Embryos in eggs laid at high altitudes are confronted with the problem that gases diffuse more rapidly at low barometric pressure than at sea level. Data on birds breeding up to 4500 m indicate that modifications in eggshell structure and embryonic physiology foster successful development in these groups. At moderate altitudes (up to 3600 m), shell conductance to gases (corrected to 760 torr) is decreased in approximate proportion to the reduction in barometric pressure, thus offsetting the increased tendency of gases to diffuse. At altitudes above 4000 m, the conductance is increased above levels at moderate altitudes, thus fostering improvement in oxygen availability, while increasing rates of water and CO2 losses. Above 4000 m, embryonic physiological properties become increasingly important for coping with hypoxic, hypocapnic, and dehydrated conditions inside the shell. Nothing is known about characteristics of eggshells and embryos in eggs laid between 4500 and 6500 m. Despite years of artificial selection, domestic fowl do not breed successfully much above 3000 m. Embryos of domestic fowl appear highly sensitive to the effects of hypoxia.     

Some Physical and Chemical Properties of Nuclease P1

The inhibitory action of compressed hydrocarbon gases on the growth of the yeast Saccharomyces cerevisiae was investigated quantitatively by microcalorimetry. Both the 50% inhibitory pressure (IP₅₀) and the minimum inhibitory pressure (MIP), which are regarded as indices of the toxicity of hydrocarbon gases, were determined from growth thermograms. Based on these values, the inhibitory potency of the hydrocarbon gases increased in the order methane << ethane < propane < i-butane < n-butane. The toxicity of these hydrocarbon gases correlated to their hydrophobicity, suggesting that hydrocarbon gases interact with some hydrophobic regions of the cell membrane. In support of this, we found that UV absorbing materials at 260 nm were released from yeast cells exposed to compressed hydrocarbon gases. Additionally, scanning electron microscopy indicated that morphological changes occurred in these cells.     

咽喉部高频喷射通气调节各参数对狗肺通气效率的影响

用相关和回归处理方法,研究了8条正常狗咽喉部高频喷射通气时,调节驱动压、呼吸比和频率对喷气量、吸入气氧浓度、动脉血气及气道内压的作用。结果显示,驱动压和呼吸此对各观察指标几乎有同等重要的作用,频率的影响很小,喷气量与吸入气氧浓度、动脉血气、气道内压间存在显著的正相关关系。说明调节参数的意义主要在于改变了喷气量。     

Effects of small nonpolar molecules on membrane compressibility and permeability: A theoretical study of the effects of anesthetic gases

We explore from a theoretical perspective the effects of small nonpolar molecules, such as anesthetic gases, on membrane compressibility and permeability. As a model system we expand a previously proposed generalization of Nagle's model for biomembrane phase transitions. In this model anesthetic gases alter membrane compressibility, causing profound changes in membrane permeability. Anesthetics either increase or decrease membrane permeability, depending on whether the membrane lipid is originally in the solid or melted state, or in a two-phase region. These changes are reversed by high pressure, in agreement with experimental results. Anesthetic-induced changes in compressibility are predicted to inhibit fusion of phospholipid vesicles to each other and to planar bilayers, and thus might be expected to inhibit the fusion of presynaptic vesicles with the presynaptic nerve membrane. This work provides a detailed molecular theory for many of the effects of anesthetic gases on both synapse and axon, and provides a coherent framework for understanding diverse experimental results.     

Pressurized freezing for retarding shrinkage after drying: a quantitative interpretation

Certain gases, when dissolved at high pressure in foods and biological materials, give a structure of gas bubbles inflating cells after freezing, depressurization, and thawing. This phenomenon has been found to reduce shrinkage after subsequent drying. The effect is interpreted quantitatively in terms of the needs for (a) a sufficient solubility of the gas in the water of the tissue at high pressure so that the Bunsen coefficient is high enough (at least 1.5 cm³/cm³ for maximum effect), and (b) a sufficiently low permeability, expressed as the product of atmospheric solubility and diffusivity in water (equal to or less that of air for maximum effect).     

Evidence for Hygrometric Pressurization in the Internal Gas Space of Spartina alterniflora

Higher pressure, up to several hundred pascal relative to ambient, is generated by hygrometric pressurization within the central hollow space of the stem in Spartina alterniflora. Dilution of oxygen and nitrogen by water vapor within the plant's internal gas space results in an influx of nitrogen and oxygen from the air and a net increase in the internal gas pressure at steady state. The nature of the pressure gradient suggests that small pores exist in the plant tissues. Moreover, the compact arrangement of leaf mesophyll cells creates a high resistance for the mass flow of gases and contributes to the higher pressure within leaves. After experimentally venting the internal pressure, outside air diffused through the basal area of the adaxial side of the leaves into the internal space and elevated pressure was restored.     

Evidence for Mass Flow in Flowering Individuals of the Submersed Vascular Plant Myriophyllum heterophyllum

Myriophyllum heterophyllum Michx. is a rhizomatous submersed aquatic plant that produces a short, emergent floral spike. We hypothesized that lacunar pressures in emergent spikes should be at or near atmospheric pressure and that a mass flow of gases from submersed stems through the rhizome to emergent stems may occur as lacunar O2 concentrations and pressures in submersed stems increase during photosynthesis. We examined the potential for a pressure gradient ([delta]P) to develop along this pathway by measuring diurnal changes in lacunar gas composition and pressure in submersed stems of nonflowering plants and emergent stems of flowering individuals. Methane release from emergent spikes was also monitored during three diurnal cycles to evaluate the hypothesis that the [delta]P is maintained by the release of lacunar gases to the atmosphere. Lacunar O2 concentrations and pressures in submersed stems increased at sunrise and reached maximum levels by midday. Although O2 fluctuated similarly in emergent stems, lacunar pressures remained at or near atmospheric pressure, indicating that a [delta]P is generated between submersed and emergent stems during photosynthesis. Methane release from emergent spikes increased as lacunar pressures increased, indicating that rhizome gases are transported through emergent stems by mass flow and the [delta]P is maintained by venting lacunar gases from emergent spikes. The potential for mass flow in both flowering and nonflowering individuals is discussed.