Oxygen transport during steady-state submaximal exercise in chronic hypoxia

Arterial O2 delivery during short-term submaximal exercise falls on arrival at high altitude but thereafter remains constant. As arterial O2 content increases with acclimatization, blood flow falls. We evaluated several factors that could influence O2 delivery during more prolonged submaximal exercise after acclimatization at 4,300 m. Seven men (23 +/- 2 yr) performed 45 min of steady-state submaximal exercise at sea level (barometric pressure 751 Torr), on acute ascent to 4,300 m (barometric pressure 463 Torr), and after 21 days of residence at altitude. The O2 uptake (VO2) was constant during exercise, 51 +/- 1% of maximal VO2 at sea level, and 65 +/- 2% VO2 at 4,300 m. After acclimatization, exercise cardiac output decreased 25 +/- 3% compared with arrival and leg blood flow decreased 18 +/- 3% (P less than 0.05), with no change in the percentage of cardiac output to the leg. Hemoglobin concentration and arterial O2 saturation increased, but total body and leg O2 delivery remained unchanged. After acclimatization, a reduction in plasma volume was offset by an increase in erythrocyte volume, and total blood volume did not change. Mean systemic arterial pressure, systemic vascular resistance, and leg vascular resistance were all greater after acclimatization (P less than 0.05). Mean plasma norepinephrine levels also increased during exercise in a parallel fashion with increased vascular resistance. Thus we conclude that both total body and leg O2 delivery decrease after arrival at 4,300 m and remain unchanged with acclimatization as a result of a parallel fall in both cardiac output and leg blood flow and an increase in arterial O2 content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Isolation of the vitellogenin-binding protein from locust ovaries

A rapid, efficient procedure for the isolation and purification of the vitellogenin binding protein from locust ovarian membranes is described. After solubilization with the nonionic detergent octyl-β-D-glucoside and removal of the detergent, the binding protein is subjected to affinity chromatography on vitellogenin coupled covalently to Affi-Gel 15. The binding protein is eluted with suramin and EDTA at low pH value. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis reveals a polypeptide with a molecular weight of 156,000 in the eluted fraction. By ligand blotting this polypeptide could be identified as the vitellogenin binding protein. It retains its high-affinity binding properties. The specific binding of vitellogenin increases from 4.8 μg (intact ovarian membranes) to 170.9 μg (affinity purified binding protein) per mg membrane protein, which corresponds to a purification factor of 35.     

Biomechanical measurements on scaphoid bone screws in an experimental model

A number of screws commonly used for internal fixation in scaphoid bone fractures and nonunions are compared regarding biomechanical properties and clinical applicability. The experiments were carried out on models made of ash-wood, representing a reconstruction and fixation as is performed in a cortico-cancellous inlay bone graft for scaphoid non-union. For fixation use was made of 2.7 and 3.5 AO/ASIF cortical screws respectively, 4.0 AO/ASIF cancellous screws, Herbert screws, and a newly designed screw called the three components screw (D.K.S.). The models with implanted screws were tested for bending strength, tensile strength and torsion stability. No large differences between the various screws were found regarding the measured parameters, so that a small intra-osteal implant such as the Herbert screw and the D.K.S., which can be inserted easily and which gives a certain amount of interfragmentary compression, will be sufficient for osteosynthesis of the scaphoid bone. In case an intra-osteal implant is not available a single 3.5 AO/ASIF cortical screw, inserted following lag-screw principles, is recommended.     

β-Dl-Methylene-aspartate,an inhibitor of aspartate aminotransferase,potently inhibitsl-glutamate uptake into astrocytes

[³H]Glutamate uptake into astrocytes in primary culture was potently inhibited by the aspartate analoguesl- andd-aspartic acid,Dl-threo--hydroxy-aspartic acid,l-aspartic acid--hydroxymate (IC50's: 136, 259, 168, and 560 M, respectively) and by -Dl-methylene-aspartate, a suicide inhibitor of asparate aminotransferase (IC50: 524 M), and by the endogenous sulphur-containing amino acidl-cysteinesulfinic acid (IC50: 114 M). [³H]Glutamate uptake was not significantly affected by either N-methyl-d-aspartate orDl-homocysteine thiolactone. These results demonstrate that other excitatory amino acids including aspartate andl-cysteinesulfinic acid (but excludingl-homocysteic acid) interact with the glutamate transport system of astrocytes. Inhibition of glutamate uptake may significantly increase the level of neuronal excitability.     

Role of the flagellum in cell-cycle-dependent expression of bacteriophage receptor activity in Caulobacter crescentus.

The rate of adsorption of Caulobacter bacteriophage phi CbK to Caulobacter crescentus is dependent on the structural integrity of the flagellum. Cells lacking part or all of the flagellum because of either mutation or mechanical shear were defective in adsorption, and the extent of the defect in adsorption reflected the amount of flagellar structure missing. Maximal adsorption rates were also dependent on cellular motility and energy metabolism, since adsorption to cells with paralyzed flagella was slower than adsorption to motile cells and inhibition of cellular energy metabolism with azide also reduced adsorption rates, even for nonmotile cells. Nevertheless, the flagellum is not the receptor for phage phi CbK, since flagellumless mutants adsorbed phi CbK at detectable rates. While some portion of the fluctuation in the phi CbK receptor activity during the C. crescentus cell cycle can be ascribed to the periodicity of flagellar loss and reappearance, the phage receptor activity remaining in flagellumless mutants was periodic in the cell cycle. Therefore, the periodic expression of phage receptor activity is an intrinsic property of the C. crescentus cell cycle, although the amplitude of the oscillation may be altered by the periodic expression of flagellar motility.     

Postmortem Degradation Alters Fluorographic Labeling Patterns and Affinities of Benzodiazepine Binding Proteins

To investigate the effect of endogenous proteolysis on the molecular weights of the benzodiazepine binding proteins, brains of trout, chicken, and rat were removed immediately after death and stored at room temperature for various periods of time before they were frozen. Photoaffinity labeling of membranes with [3H]flunitrazepam, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, revealed proteolytic fragments of 47K in trout, chicken, and rat. The proteolysis set in rapidly after death. Seemingly in parallel with the degradation observed fluorographically, the affinity for [3H]flunitrazepam increased without systematic changes in receptor density. The degradation pattern was not identical to that of the photolabeled trypsinized benzodiazepine binding proteins. The endogenous proteolytic fragments were deglycosylated in two steps. In conclusion, proteolytic effects must be taken into account when interpreting labeling patterns and binding parameters.     

Blood–Brain Barrier Permeability to Sodium. Modification by Glucose or Insulin?

In order to explore the pathogenetic mechanism underlying the changes in blood-brain barrier sodium transport in experimental diabetes, the effects of hyperglycemia and of hypoinsulinemia were studied in nondiabetic rats. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 20% (5.6 +/- 0.7 versus 7.0 +/- 0.8 X 10(5) ml/g/s) as compared to controls. Intravenous infusion of 50% glucose for 2 h was associated with a decrease in the blood-brain barrier permeability to sodium (5.4 +/- 1.2 X 10(5) ml/g/s), whereas rats treated with an inhibitor of insulin-secretion (SMS 201-995, a somatostatin-analogue) had normal sodium permeability (7.3 +/- 2.0 X 10(5) ml/g/s). Acute insulin treatment of diabetic rats normalized the sodium permeability within a few hours as compared to a separate control group (7.7 +/- 1.1 versus 6.9 +/- 1.4 X 10(5) ml/g/s). To elucidate whether the abnormal blood-brain barrier passage is caused by a metabolic effect of glucose or by the concomitant hyperosmolality, rats were made hyperosmolar by intravenous injection of 50% mannitol. Although not statistically significant, blood-brain barrier sodium permeability increased in hyperosmolar rats as compared to the control rats (8.3 +/- 1.0 and 7.0 +/- 1.9 X 10(5) ml/g/s, respectively). It is concluded that either hyperglycemia per se or a glucose metabolite is responsible for the blood-brain barrier abnormality which occurs in diabetes. Further, we suggest that the specific decrease of sodium permeability could be the result of glucose-mediated inhibition of the Na+K+-ATPase localized at the blood-brain barrier.     

Molecular cloning,nucleotide sequence and expression in Escherichia coli of the β-cyclodextrin glycosyltransferase gene from Bacillus circulans strain no. 8

Summary The -cyclodextrin glycosyltransferase (-CGTase) gene was isolated from a -library prepared from Bacillus circulans strain no. 8. It was subcloned into plasmid pTZ and expressed by its endogenous regulatory sequences in Escherichia coli JM 103. The structural gene was sequenced and showed an open reading frame for a polypeptide of 718 amino acid residues. The recombinant -CGTase had the same enzymatic properties as the extracellular CGTase (684 amino acid residues, corresponding to a mol. wt. of 74416) produced by B. circulans strain no. 8. The amino acid sequence showed the highest homology (74.6% identical amino acids) with the CGTase of B. circulans strain F-2, which had been erroneously described as an amylase. The homology with the enzyme from the alkalophilic Bacillus sp. strain no. 1011 was 71.4%. The amino acid sequence derived will be used for elucidating the three-dimensional structure of the enzyme. Offprint requests to: H. Bender     

FECAL METHANOGENS AND VERTEBRATE EVOLUTION

It has been assumed that the feeding habits of vertebrates predispose the variety of intestinal differentiations and the composition of the microbial biota living in their intestinal tracts. Consequently, the presence of methanogenic bacteria in the various differentiations of the large intestine and the foregut of herbivorous vertebrates had been attributed primarily to the existence of anaerobic habitats and the availability of carbon dioxide and hydrogen originating from the fermentative microbial digestion of plant-based diets. However, Australian ratites, many murids, and several New World primates lack methanogens, despite their intestinal differentiations and their vegetarian feeding habits. Crocodiles, giant snakes, aardvarks, and ant-eaters on the other hand release significant amounts of methane. A determination of methane emissions by 253 vertebrate species confirmed that competence for intestinal methanogenic bacteria is shared by related species and higher taxa, irrespective of different feeding habits. In “methanogenic” branches of the evolutionary tree, a variety of differentiations of the large intestine evolved and, in some cases, differentiations of the foregut. In contrast, the lack of competence for methanogens in chiropterans/insectivores and carnivores apparently has precluded the evolution of specialized fermenting differentiations of the digestive tract. Our observations reveal that the presence of intestinal methanogenic bacteria is under phylogenetic rather than dietary control: competence for intestinal methanogenic bacteria is a plesiomorphic (primitive-shared) character among reptiles, birds, and mammals. This competence for methanogenic bacteria has been crucial for the evolution of the amniotes.