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Biomedical subjects

J S Clegg

Publications and source records attributed to J S Clegg.

At least 55 records · Page 3Linked to original sources
PubMed1982

Cellular responses to extreme water loss: the water-replacement hypothesis.

The previously advanced hypothesis that desiccation resistance involves the replacement of water adjacent to intracellular surfaces with polyhydroxy compounds has been supported by experiments on cysts of the brine shrimp, Artemia, and in a model system of albumin--glycerol--water, using nuclear magnetic resonance spectroscopy, microwave dielectrics, and density measurements. We have also considered other problems that cells face when large fractions of their total water content are removed. Observations by other investigators have indicated that a variety of mammalian cells can lose roughly 50% of their water and survive; for a given cell type death occurs if its volume is reduced below a certain minimum level. Membrane damage has previously been suggested to be a major cause of dehydration damage. We have proposed some additional plausible mechanisms that might also be involved.

Adaptation, Physiological↗
PubMed1981

Metabolic consequences of the extent and disposition of the aqueous intracellular environment.

Attention is focused on the aqueous compartments of eucaryotic cells (nucleoplasm, cytosol, and interior compartments of cytoplasmic membrane-bound organelles). Previous work on the relationship between cell water content, the physical properties of cell water, and metabolic activity in cysts of the brine shrimp, Artemia is summarized and discussed in that context. A previously proposed general model of the organization of metabolic activity in the aqueous compartments will be summarized.

Animals↗
PubMed1978

On the residual water content of dried but viable cells.

We have examined the residual water in dried cysts of the brine shrimp, Artemia salina, by gas-bombardment techniques at reduced pressures and temperatures. This treatment reduced, but did not remove all the residual water, the lower limit being about 0.0069 gH2O/g dried weight. The significance of such small amounts of water to cell hydration is assessed. The treatment did not appreciably reduce the viability of this cyst population.

Animals↗
PubMed1978

Interrelationships between Water and cellular metabolism in Artemia cysts. VIII Sorption isotherms and derived thermodynamic quantities.

An analysis of water vapor sorption by cysts of the brine shrimp, Artemia salina, has shown that at environmental water activities (aw) of 0.95 or less, the cysts equilibrate with the aw of their environment. Above this aw the metabolic activity of the cysts participates directly in their water content, and equilibration does not occur. In contrast, dried cysts killed by heat treatment or exposure to ammonia fumes equilibrated with all values of aw examined. Analysis of the temperature dependence of sorption isotherms revealed that below cyst hydrations of about 0.3 g H2O/g dried weight the temperature coefficient for water sorption was negative, but became positive at hydrations appreciably in excess of this value. Estimates for the differential and integral net enthalpy and entropy changes accompanying the sorption of water have been calculated from isotherms. These results have been interpreted and integrated with those from previous work on the hydration-dependence of metabolic activity. All of the examined hydration properties of the cysts have been shown to be due chiefly to the cellular component, and not the acellular shell. Analysis of the data by the Bradley equation has shown that the hydration behavior of the shell obeys this relationship, whereas that of the cellular component does not.

Animals↗
PubMed1977

Interrelationships between water and cellular metabolism in Artemia cysts. VI. RNA and protein synthesis.

Using 14CO2 as a labelled precursor the relationship between the initiation of protein and RNA synthesis, and water concentration, has been examined in cysts (encysted embryos) of the brine shrimp, Artemia salina. Although incorporation of radioactivity into amino acids and nucleotides occurred in cysts at hydrations as low as 0.3 g H2O/g dried cysts, incorporation into proteins and RNA was not measurable until the cysts had achieved a hydration in the range of 0.6-0.6 g/g. In no case was radioactivity detected in DNA of unemerged cysts. Fully hydrated cysts (about 1.3 g/g) that were actively synthesizing proteins and RNA, stopped doing so when dehydrated to levels below the same hydration range: thus, the hydration dependence does not involve appreciable hysteresis. The hydration range required to initiate synthesis of these macromolecules is essentially the same as that previously shown to initiate embryonic development.

Animals↗
PubMed1977

Interrelationships between water and cellular metabolism in Artemia cysts. VII. Free amino acids.

The concentration of total ninhydrin-positive material (NPM) soluble in 5% trichloroacetic acid was measured in cysts of the brine shrimp. Artemia salina, as a function of hydration level. No net change in NPM was observed until the cysts had achieved a water content of about 0.65 g H2O/g of initially dry cysts. Above this hydration threshold the NPM content increased markedly. Examination of the free amino acid composition of cysts incubated at selected hydration levels revealed that almost all of the amino acids underwent net change above the hydration threshold. However, just below this threshold, the free amino acid composition was essentially the same as in fully dried cysts. The activity generating net changes in the concentration of free amino acids above the hydration threshold was shown to be metabolic in nature and restricted to the cellular component of the cyst.

Amino Acids↗
PubMed1976

Interrelationships between water and cellular metabolism in Artemia cysts. IV. Adenosine 5'-triphosphate and cyst hydration.

The concentration of ATP in cysts of the brine shrimp, Artemia salina, has been studied as a function of cyst hydration. Cysts dried over CaSO4 contain 0.02 gH2O/g cysts and 0.54 +/- 0.05 (S.D.) mumoles of ATP/g dried cysts. Addition of water up to 0.05 g/g cysts produced no net change in the level of ATP during incubation. Hydration levels between 0.05 and 0.62 g/g cysts resulted in a net loss of ATP, whereas above 0.65 g/g cysts a net increase was observed with incubation time. No net change in the amount of ATP, compared with dried cysts, was detected between the latter two hydrations. These results, when integrated with those from previous work, indicate that conventional aerobic energy metabolism does not begin until cyst hydrations of about 0.65 g/g are achieved. The fate of ATP in cysts hydrated to levels lower than 0.65 g/g was discussed.

Adenosine Triphosphate↗
PubMed1976

Interrelationships between water and cellular metabolism in Artemia cysts. V. 14CO2 incorporation.

The ability of cysts of the brine shrimp, Artemia salina, to incorporate 14CO2 into organic compounds soluble in cold-trichloroacetic acid was examined over a broad range of cellular water concentrations. Carbon dioxide was not incorporated by cysts containing less than about 0.3 g H2O/g dried cysts, the "critical hydration" for CO2-fixation. This relationship held whether the cysts were hydrated from the liquid or the vapor phase. The incorporation of radioactivity was shown to be due exclusively to metabolic activity in the cellular component of the cyst. Above the critical hydration, the amount of 14CO2 incorporated was a function of cyst water content, but the kinds of metabolites labelled with this precursor, and their relative proportions, were found to be similar in cysts of greatly different hydration. Almost all of the radioactivity was associated with amino acids, Krebs cycle intermediates and related acids, and pyrimidine nucleotides. The fact that the pathway involved with CO2-fixation, and subsequent metabolism of the fixation products are all initiated in cysts containing as little as 0.3 g H2O/g is particularly noteworthy since this hydration level is well within the range of the amounts of "bound water" described in the literature for a wide array of cells and tissues.

Amino Acids↗