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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The study of glucose-induced proton fluxes in Saccharomyces cerevisiae NCYC 431 showed a decrease of proton net efflux by ethanol across the plasma membrane of energized cells. Furthermore a negative net proton efflux (an influx) occurred from a given ethanol concentration (between 1.3 and 1.5 M) whatever the experimental conditions used, thus allowing the definition of a nil-net exchange step where no net movement of protons across the plasma membrane could be observed. A new technique of ethanol tolerance determination in yeast based upon a correlation for the same ethanol concentration between both the collapse of the proton gradient and the growth cessation in cultures supplemented with ethanol after 8 h incubation was proposed. The defined method also showed a cumulated effect of temperature and ethanol on Saccharomyces cerevisiae NCYC 431.
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PMID:Effect of ethanol on the glucose-induced movements of protons across the plasma membrane of Saccharomyces cerevisiae NCYC 431. 303 91

A simple method for electron microscopic preparation of plant protoplasts is described. The main problems in preparing these fragile protoplasts for electron microscopy have been cell collapse due to steep gradients between protoplasts and fixatives and unacceptable loss of material during the many steps of the procedure. These problems may be solved by immobilization of the protoplasts in calcium alginate beads. The free diffusion properties of this gel prevent steep gradients. The beads also simplify handling and prevent loss of material. Protoplasts isolated from hypocotyls of rape, Brassica napus (var. Niklas), have been used as a model system. Transmission electron microscopy of the immobilized protoplasts osmotically stabilized with glucose demonstrated adequate structural and ultrastructural preservation.
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PMID:Plant protoplasts immobilized in calcium alginate: a simple method of preparing fragile cells for transmission electron microscopy. 317 77

Blood flow rate in a vascular network is proportional to the pressure difference between the arterial and venous sides and inversely proportional to the viscous and geometric resistances. Despite rapid progress in recent years, there is a paucity of quantitative data on these three determinants of blood flow in tumors and several questions remain unanswered. This paper reviews our current knowledge of these three parameters for normal and neoplastic tissues, the methods of their measurements, and the implications of the results in the growth and metastasis formation as well as in the detection and treatment of tumors. Microvascular pressures in the arterial side are nearly equal in tumor and nontumorous vessels. Pressures in venular vessels, which are numerically dominant in tumors, are significantly lower in a tumor than those in a nontumorous tissue. Decreased intravascular pressure and increased interstitial pressure in tumors are partly responsible for the vessel collapse as well as the flow stasis and reversal in tumors. The apparent viscosity (viscous resistance) of blood is governed by the viscosity of plasma and the number, size, and rigidity of blood cells. Plasma viscosity can be increased by adding certain solutes. The concentration of cells can be increased by adding cells to blood or by reducing plasma volume. The rigidity of RBC, which are numerically dominant in blood, can be increased by lowering pH, elevating temperature, increasing extracellular glucose concentration, or making the suspending medium hypo- or hypertonic. Effective size of blood cells can be increased by forming RBC aggregates (also referred to as rouleaux). RBC aggregation can be facilitated by lowering the shear rate (i.e., decreasing velocity gradients) or by adding macromolecules (e.g., fibrinogen, globulins, dextrans). Since cancer cells and WBC are significantly more rigid than RBC, their presence in a vessel may also increase blood viscosity and may even cause transient stasis. Finally, due to the relatively large diameters of tumor microvessels the Fahraeus effect (i.e., reduction in hematocrit in small vessels) and the Fahraeus-Lindqvist effect (i.e., reduction in blood viscosity in small vessels) may be less pronounced in tumors than in normal tissues. Geometric resistance for a network of vessels is a complex function of the vascular morphology, i.e., the number of vessels of various types, their branching pattern, and their length and diameter. Geometric resistance to flow in a single vessel is proportional to the vessel length and inversely proportional to vessel diameter to the fourth power.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Determinants of tumor blood flow: a review. 328 47

The rate at which Z. mobilis (Entner-Doudoroff pathway) converts high concentrations of glucose (20%) into ethanol plus CO2 changes as ethanol accumulates in the surrounding broth. This decline in glycolytic activity (per milligram of cell protein) does not result from inhibitory effects of ethanol, which can be reversed immediately by ethanol removal. The peak of fermentative activity (58 mumol of CO2 evolved per mg of cell protein per h) occurred after the accumulation of 1.1% ethanol (18 h) and declined to one-half this rate after 30 h (6.2% accumulated ethanol), although the cell number continued to increase. These times corresponded to the end of exponential growth and to the onset of the stationary phase (on the basis of measurement of cell protein), respectively. An examination of many of the requirements for fermentation (nucleotides, magnesium, enzyme levels, intracellular pH, delta pH) revealed three possible reasons for this early decline in activity: decreased abundance of nucleotides, a decrease in internal pH from 6.3 to 5.3, and a decrease in the specific activities of two glycolytic enzymes (pyruvate kinase and glyceraldehyde-3-phosphate dehydrogenase). 31P nuclear magnetic resonance spectra of perchlorate extracts from cells fermenting in broth revealed very low levels of glycolytic intermediates (Entner-Doudoroff pathway) in cells examined at the peak of fermentative activity (18-h cells) in comparison with cells examined at a later stage (30-h cells), consistent with limitation of the fermentation rate by glycolytic enzymes near the end of the pathway. It is likely that cell death (loss of colony-forming ability) and the collapse of delta pH also contribute to the further decline in fermentative activity after 30 h.
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PMID:Glycolytic flux in Zymomonas mobilis: enzyme and metabolite levels during batch fermentation. 361 Oct 27

In C6 astrocytoma cells respiring with glucose, 40% of the total production of ATP was provided by glycolysis. Anaerobiosis in the presence of glucose, reduced ATP synthesis by approximately 50%, increased lactate production by 30% and caused a 3-fold decline in [creatine phosphate]/[creatine] and consequently [ATP]free[ADP]free. There was no change in [K+]i which suggests that glycolytic production of ATP provides sufficient energy to ensure normal operation of the Na+/K+ pump. In the absence of glucose, [creatine phosphate]/[creatine] declined to less than 0.1 in 15 min and there was a loss of K+ from cells. A comparison of delta GATP and delta GNa,K under aerobic conditions with and without glucose, showed the former to be larger by 1 - 2 kcal. However, under O2-limited, glucose-restricted conditions delta GATP fell below the level necessary to maintain operation of the Na+/K+ pump and led to a collapse in ionic gradients.
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PMID:Energy relationships between ATP synthesis and K+ gradients in cultured glial-derived cell line. 367 41

The possibility that pulmonary surfactant, characterized by a phosphatidylglycerol deficiency, as in early fetal life, might have inferior surface properties was evaluated. We obtained this specific surfactant from adult rabbits by withholding glucose and giving them an excess of myoinositol by mouth and intravenously. Controls were given a similar quantity of glucose. The myoinositol resulted in a drastic reduction of surfactant phosphatidylglycerol, from 7.2 to 0.3% of phospholipids, and a corresponding increase in phosphatidylinositol from 4.8 to 11.3%. In addition, the myoinositol treatment increased the myoinositol that was disaturated from 18.5 to 27.3% (p less than 0.05). The corresponding figures for disaturated phosphatidyl-choline were 56.0 and 60.5%, respectively (NS). The myoinositol treatment for 4 days increased the pool size of alveolar surfactant by 32% (p less than 0.01). The surface activity was studied with modified Wilhelmy balance and the pulsating bubble surfactometer. Surfactant containing phosphatidylinositol rather than phosphatidylglycerol was not inferior, as compared to surfactant that contained phosphatidylglycerol (minimum surface tension: 2.0 versus 2.2 mN X m-1; collapse rate at 10 nM X m-1: 1.85 versus 1.95 min-1; rate of adsorption from subphase to surface: 32 versus 35 mN X m-1 X 30 s-1), nor was there a difference in the ability of the two surfactants to improve lung stability of 27-day-old rabbit fetuses (air retention at 35 cm H2O: 1.8 versus 1.8 ml/30 g; air retention at 0 cm H20: 0.8 versus 0.9 ml/30 g). We conclude that phosphatidylinositol surfactant does not have inferior surface properties.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Composition and surface activity of normal and phosphatidylglycerol-deficient lung surfactant. 383 83

Glucose-insulin-potassium (GIK) improves myocardial function during endotoxin shock but the mechanism of this action is not clear. We have studied in open chest dogs the effects of GIK (n = 9) on haemodynamics, myocardial biochemistry (repeated drill biopsies; glucose-6-phosphate, G-6-P; fructose-6-phosphate, F-6-P; adenosine triphosphate, ATP; creatinine phosphate, CP; glycogen) and myocardial histomorphometry. The animals were anaesthetised (etomidate 4 mg X kg-1 X h-1) and artificially ventilated (N2O:O2 = 2:1). After endotoxin (1.5 mg X kg-1) cardiac output (CO) and mean arterial pressure (MAP) fell rapidly, with a temporary recovery followed by gradual circulatory collapse. Coronary blood flow (cbf; radioactive microspheres) decreased, but this was not significant. G-6-P tended to fall, as did ATP levels while CP levels were unaltered. Histomorphometrical analysis showed myocardial cell swelling with compression of capillaries and decreased interstitial volume. GIK infusion (50% glucose, 2 g X kg-1bw, 8 mmol KCl and 3 U insulin kg-1bw) increased CO and coronary blood flow. Glycogen and G-6-P levels did not change, while F-6-P tended to increase. ATP levels were not influenced by ATP/CP ratio decreased. Myocardial cell swelling markedly decreased; average capillary cross-sectional area, as an index of capillary compression, returned to control value. In two dogs, which died before the end of the experiment, myocardial oedema, with disturbed capillary volume and reduced interstitial volume was unaltered after GIK. The initial effects of GIK are most likely due to restoration of myocardial perfusion. Improved perfusion, and the influence of elevated serum osmolality and insulin levels on excitation-contraction coupling may help to improve myocardial function.
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PMID:Myocardial metabolic and morphometric changes during canine endotoxin shock before and after glucose-insulin-potassium. 389 58

Total parenteral nutrition is one of the most important recent advances in medicine. The delivery of total parenteral nutrition, however, can be associated with a broad spectrum of complications ranging from mechanical (catheter related) to metabolic. We have recently seen a previously unreported complication of total parenteral nutrition - three patients maintained on total parenteral nutrition, who did not receive vitamins and experienced the acute onset of life-threatening metabolic acidosis with pH values as low as 6.70. All responded promptly and completely to the administration of intravenous thiamine, and thus were probably examples of acute beriberi. Acute beriberi is a well-documented syndrome which usually occurs in nutritionally compromised individuals outside the hospital setting who lack thiamine in their diet. Without thiamine, glucose cannot enter the Krebs cycle in order to be completely oxidized for energy production and therefore, accumulates as lactic acid. This lactic acidosis is refractory to any treatment except thiamine and will result in cardiovascular collapse if the vitamin is not administered.
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PMID:Severe acute metabolic acidosis (acute beriberi): an avoidable complication of total parenteral nutrition. 392 38

We prepared ten dogs with intraperitoneal catheters to allow total nutritional support for 30 days by constant infusion of a solution containing 1.5% amino acid, 10% glucose, and 1% lipids at a rate of 4 ml/kg/hr. Seven dogs survived in apparent good health but with a 13.9 +/- 1.3% weight loss. There was no correlation between actual caloric input and percentage of weight loss. Serum albumin concentration fell to 2.6 +/- 0.3 gm/dl but other chemistries remained near normal. The peritoneum showed significant inflammatory reaction but this resolved by 30 days. Three dogs died in the first week from what appeared to be circulatory collapse from rapid fluid shifts. We conclude that a significant amount of nutrients can be delivered through the peritoneal cavity but whether total nutritional support is feasible remains to be proven.
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PMID:Total nutritional support through the peritoneal cavity. 393 May 90

When spores of Bacillus megaterium ATCC 12872 were incubated with CdCl2, they germinated without decomposition of the cortex. Moreover, the volume ratio of cortex to protoplast-plus-cortex, C/(P+C), of the CdCl2-germinated spores was reduced. Incubation of isolated cortex with the divalent compounds Cd2+, Ca2+, and Mg2+ reduced the gel volume to about 1/5 but incubation with a nonionic compounds, glucose, did not. The spores with reduced C/(P+C) were observed in the early period of glucose-induced germination. The time required for a 50% change in cortex morphology to occur was 2.5 min, which corresponds well with the time for 50% loss of heat resistance. This time was shorter than that necessary for release of peptidoglycan fragments and hydrolysis of cortex glycan chains. These data indicate that cortex hydrolysis is not related to the initiation of germination. 50% of the dipicolinic acid, calcium and magnesium were released at 3.4, 4.0, and 2.4 min, respectively. These results suggest that collapse of cortex expansion by the interaction of cortex with dipicolinic acid and cations released from the core, or exogenous ionic germinants is an important step in the initiation of germination.
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PMID:Collapse of cortex expansion during germination of Bacillus megaterium spores. 393 4


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