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Biomedical subjects

J W Porteous

Publications and source records attributed to J W Porteous.

At least 19 recordsLinked to original sources
PubMed2005

Henrik Kacser--a neglected author?

All sciences progress by elaborating new concepts and by finding new relationships between the parts of a system of interacting components. Henrik Kacser, with a background in Biophysics and Genetics, was well placed to develop a new and comprehensive analysis of the control of metabolic fluxes and metabolite concentrations; and to demonstrate that changes in the concentration of normal metabolites were as important in Genetics as changes in the composition of metabolites in bringing about a change in trait.

Animals↗
PubMed1996

Dominance--one hundred and fifteen years after Mendel's paper.

In The Molecular Basis of Dominance, Kacser & Burns (1981) demonstrated that dominance in diploids and polyploids, and pleiotropy in all organisms, were biochemical phenomena; they were the consequences of the response of a metabolic system to a genetically specified change in the activity of any one enzyme within the system. Epistasis was similarly explicable when each of at least two enzyme activities suffered a change. The significance of this achievement by Kacser & Burns (1981) for biochemistry, genetics, molecular biology, medicine and bio-technology is best seen against the background of 115 years of attempts to explain the origins of dominance.

Animals↗
PubMed1994

Glucose translocation and metabolism in the rat jejunum perfused in once-through mode in vitro.

Simultaneous once-through luminal and vascular perfusions with glucose of rat jejunum in vitro were used in an attempt to resolve conflicting reports on glucose metabolism in jejuna perfused in once-through mode in vivo and in recirculation mode in vitro. Results include: (a) respiration rates during each perfusion, (b) CO2 production from absorbed glucose, (c) absolute rates of glucose absorption from the lumen into the epithelium, (d) absolute rates of glucose translocation from lumen to vascular bed, (e) absolute rates of lactate excretion into the two perfusion media, (f) recoveries of absorbed glucose, (g) the distribution of radioactivity among translocated glucose and its metabolites. About 50% of the total lactate originates in the glucose extracted from the vascular medium during concomitant absorption and translocation of luminal glucose. The results suggest what further experiments need to be done. Results from recirculation perfusions in vitro cannot contest or confirm the results quoted from experiments conducted with once-through perfusions in vivo.

Animals↗
PubMed1991

Lactate is not a major product of glucose metabolism in the respiring jejunum perfused in the recirculation mode in vitro.

Yields of lactate from glucose absorbed from the luminal medium and extracted concurrently from the vascular medium of the perfused rat jejunum in vitro were half those previously reported from comparable glucose concentrations in the recirculated perfusion media. These low yields were obtained by maintaining perfusion medium flow rates and pressures pharmacologically at values found in vivo; permitting normal peristalsis; and restoring the depleted glyceric acid-2,3-bisphosphate and reduced deformability of out-dated blood-bank erythrocytes to normal physiological values before they were added to the vascular perfusion medium and equilibrated at 37 degrees C with air/CO2. Respiration rates are recorded for the first time in each perfusion experiment. A substantial fraction of glucose consumed in this and all earlier recirculation perfusion experiments in vitro has still to be accounted for.

Animals↗
PubMed1991

The vascularly and luminally perfused small intestine in vitro: dissection technique and model system.

The quantitative study in vitro of a wide range of intestinal functions is best achieved by perfusing the intestine simultaneously by the luminal and vascular routes. A comprehensive description is given of the dissections involved in preparing a selected segment of jejunum for such simultaneous perfusions. Attention is drawn to a number of occasional aberrant vascular structures which require special attention if successful perfusions are to be established. It is essential to restore the ATP and diphosphoglycerate concentrations of erythrocytes, and to assess their deformability, before incorporating them in the vascular perfusion medium. The perfusion equipment, the perfusion media and the general conduct of a perfusion experiment, are described.

Anesthesia↗
PubMed1980

Changes in the synthesis of ribosomal ribonucleic acid and of poly(A)-containing ribonucleic acid during the differentiation of intestinal epithelial cells in the rat and in the chick.

Epithelial cells were isolated from rat and chick small intestine by techniques which separated subpopulations of differentiating villus and upper crypt cells from each other and from populations of mitotically dividing lower crypt cells. Incorporation of precursors into epithelial-cell DNA, cytoplasmic rRNA and cytoplasmic poly(A)-containing RNA occurred in the lower crypt cells in vivo when precursor was supplied from the vascular system of the intestine. Incorporation of precursor into 28S and 18S rRNA continued in the upper crypt cells, but occurred to only a very slight extent (if at all) in villus cells, whereas incorporation into poly(A)-containing RNA continued (at a diminishing rate) as the differentiating cells migrated along the villi. When precursor was supplied from the intestinal lumen, its incorporation into DNA and into rRNA of crypt cells was not very different from that observed with the other mode of precursor administration, but incorporation into villus-cell poly(A)-containing RNA then occurred at essentially the same rate in all intestinal epithelial cells in vivo. Cytoplasmic poly(A)-containing RNA appeared to turn over in rat crypt cells with a half-life not exceeding 24 h; crypt-cell rRNA showed no turnover and no evidence could be found for the presence of 'metabolic DNA'.

Animals↗
PubMed1980

Glutamate, glutamine, aspartate, asparagine, glucose and ketone-body metabolism in chick intestinal brush-border cells.

1. Suspensions of isolated chick jejunal columnar absorptive (brush-border) cells respired on endogenous substrates at a rate 40% higher than that shown by rat brush-border cells. 2. Added d-glucose (5 or 10mm), l-glutamine (2.5mm) and l-glutamate (2.5mm) were the only individual substrates which stimulated respiration by chick cells; l-aspartate (2.5 or 6.7mm), glutamate (6.7mm), glutamine (6.7mm), l-alanine (1 or 10mm), pyruvate (1 or 2mm), l-lactate (5 or 10mm), butyrate (10mm) and oleate (1mm) did not stimulate chick cell respiration; l-asparagine (6.7mm) inhibited slightly; glucose (5mm) stimulated more than did 10mm-glucose. 3. Acetoacetate (10mm) and d-3-hydroxybutyrate (10mm) were rapidly consumed but, in contrast to rat brush-border cells, did not stimulate respiration. 4. Glucose (10mm) was consumed more slowly than 5mm-glucose; the dominant product of glucose metabolism during vigorous respiration was lactate; the proportion of glucose converted to lactate was greater with 10mm- than with 5mm-glucose. 5. Glutamate and aspartate consumption rates decreased, and alanine and glutamine consumption rates increased when their initial concentrations were raised from 2.5 to 6.7 or 10mm. 6. The metabolic fate of glucose was little affected by concomitant metabolism of any one of aspartate, glutamate or glutamine except for an increased production of alanine; the glucose-stimulated respiration rate was unaffected by concomitant metabolism of these individual amino acids. 7. Chick cells produced very little alanine from aspartate and, in contrast to rat cells, likewise produced very little alanine from glutamate or glutamine; in chick cells alanine appeared to be predominantly a product of transmination of pyruvate derived from glucose metabolism. 8. In chick cells, glutamate and glutamine were formed from aspartate (2.5 or 6.7mm); aspartate and glutamine were formed from glutamate (2.5mm) but only aspartate from 6.7mm-glutamate; glutamate was the dominant product formed from glutamine (6.7mm) but aspartate only was formed from 2.5mm-glutamine. 9. Chick brush-border cells can thus both catabolize and synthesize glutamine; glutamine synthesis is always diminished by concomitant metabolism of glucose, presumably by allosteric inhibition of glutamine synthetase by alanine. 10. Proline was formed from glutamine (2.5mm) but not from glutamine (2.5mm)+glucose (5mm) and not from 2.5mm-glutamate; ornithine was formed from glutamine (2.5mm)+glucose (5.0mm) but not from glutamine alone; serine was formed from glutamine (2.5mm)+glucose (5mm) and from these two substrates plus aspartate (2.5mm). 11. Total intracellular adenine nucleotides (22mumol/g dry wt.) remained unchanged during incubation of chick cells with glucose. 12. Intracellular glutathione (0.7-0.8mm) was depleted by 40% during incubation of respiring chick cells without added substrates for 75min at 37 degrees C; partial restoration of the lost glutathione was achieved by incubating cells with l-glutamate+l-cysteine+glycine.

Adenine Nucleotides↗
PubMed1979

Poly(adenosine diphosphate ribose) synthetase activity in nuclei of dividing and of non-dividing but differentiating intestinal epithelial cells.

Poly(ADP-ribose) synthetase activity is found in nuclei of regenerating epithelial cells in the lower half of the crypts of guinea-pig small intestine. Nuclei from non-dividing but differentiating and maturing cells in the upper crypts and on the villi contain no more than about 10% of the synthetase activity of lower-crypt cell nuclei. The product in the active nuclei is shown to be 80% poly(ADP-ribosylated) protein and 20% mono(ADP-ribosylated) protein; 60% of thetotal labelled product was attached to acid-soluble proteins (including histones), and 40% to acid-insoluble (non-histone) proteins. The average number of ADP-ribosyl units in the oligomeric chains of the poly(ADP-ribosylated) proteins was 15 but the range of sizes of (ADP-ribose) oligomers attached to nuclear proteins was smaller in villus than in crypt cell nuclei.

ADP Ribose Transferases↗
PubMed1979

Intestinal metabolism.

The anatomy of the intestine is outlined. The kinetics of cell proliferation, differentiation, and migration in intestinal epithelium are described. The distribution of cell types between the proliferation and differentiation compartments of the epithelium is summarized. Seven preparations of intestine in current use for metabolic studies are listed. An outline review is presented of recent results on glucose, amino acid and ketone body metabolism obtained with three of these preparations: the ligature-isolated loop of intestine in vivo; the vascularly and luminally perfused intestine in vitro; and suspensions of respiring intestinal epithelial cells in vitro. Reasons are given for thinking that these experimental systems are among the most useful currently available for metabolic studies, perhaps especially in the investigation of the metabolic fate of potentially toxic materials to which animal species may be exposed.

Amino Acids↗
PubMed1978

Characterization of columnar absorptive epithelial cells isolated from rat jejunum.

The origin and yield of cells isolated from rat jejunum have been assessed; 80-90% of the mature columnar absorptive cells but none of the Paneth, endocrine or regenerating crypt cells were recovered by the methods described. The structural integrity of the isolated cells was tested by phase contrast-, Nomarski interference- and fluorescence light-microscopy; and also by transmission electron microscopy; the isolated cells appeared structurally intact by all microscopic criteria applied. The isolated cells were judged to be functionally intact because they satisfied a number of tests designed to answer three logically related questions, namely: was the cell-surface membrane intact; were the cells able to accumulate selected solutes against a concentration gradient from the exterior medium; and were the cells able to perform biochemical functions which depended upon the integrated activities of several subcellular structures? The isolated cells did retain and accumulate selected solutes, respired at a steady rate on endogenous substrates, showed enhanced respiration on exogenous glucose and glutamine, maintained favourable intracellular proportions of adenine nucleotides (ATP:ADP:AMP), and synthesized cell protein from extracellular amino acids in proportion to the time of incubation. The isolated cells accounted for 80% of the lactic acid produced by intact rat jejunum under similar conditions of incubation.

Adenine Nucleotides↗
PubMed1977

Steady-state metabolism and transport of D-glucose by rat small intestine in vitro.

1. Conditions of incubation of everted sacs of rat small intestine were selected to ensure that absorption of d-glucose by mucosal tissue from the incubation medium, intracellular metabolism of the absorbed glucose and transport of glucose through the intact intestinal tissue proceeded linearly with respect to time of incubation within stated time intervals. 2. Under these experimental conditions, steady intracellular concentrations of glucose and lactate were demonstrated. 3. The quantitative translocational and metabolic fate of absorbed glucose was determined under these steady-state conditions. About 25% of glucose absorbed from the external mucosal solution was accumulated (temporarily) within mucosal tissue and about 25% transported through the intact tissue into the external serosal solution; the remainder (about 50%) of the absorbed glucose was metabolized, 90% to lactate and 10% to CO(2). Concomitant respiration rates were comparable with those reported for several other preparations of intestine and were stoicheiometrically in excess of the O(2) metabolism required to account for the production of CO(2) from the absorbed glucose. 4. Water transport through the everted sacs proceeded at an optimum rate under the experimental conditions selected. 5. Some other observations are recorded which influenced the design of the experiments and the interpretation of results; these include the initial physiological state of the animal, the anaesthetic used and the ionic composition of the incubation medium.

Animals↗
PubMed1965

The isolation and properties of epithelial-cell "ghosts" from rat small intestine.

1. The preparation of gram quantities of isolated epithelial-cell ;ghosts' from mucosal scrapings of rat small intestine is described. The method involves dispersing the tissue by gentle homogenization in 6% dextran in Krebs-Ringer phosphate, pH7.4, followed by filtration through nylon cloth and sedimentation by low-speed centrifuging. 2. The isolated epithelial-cell ;ghosts' contained all of the DNA, but only 52% of the protein and 53-57% of the RNA of the original homogenate. They contained most of the activity of the following enzymes found in the homogenate: aminopeptidase (71%); alkaline beta-glycerophosphatase (82%); invertase (92%); adenosine triphosphatase (93-116%); acid beta-glycerophosphatase (83%); nonspecific esterase (76%); succinate dehydrogenase (96%). Only small proportions of the total lactate-dehydrogenase (10%) and phosphoglucose-isomerase (2%) activities found in the homogenate were recovered in the isolated cell ;ghosts'. 3. The epithelial-cell ;ghost' preparation did not respire unless cofactors and substrates were added, and did not consume glucose or produce lactic acid from glucose. 4. The effect of varying the composition of the homogenization medium was studied. Concentrations of dextran (mol.wt. 15x10(4)) from 1 to 12%, solutions of dextrans (all at 6%) with mol.wt. varying between 3.6x10(4) and 2x10(6), and a solution of 8% polyethylene glycol (mol.wt. 4000) served equally well for the production of epithelial-cell ;ghosts'. Two of these solutions, however, 12% dextran (mol.wt.15x10(4)) and 6% dextran (mol.wt. 2x10(6)), were too viscous to allow the complete sedimentation of the cell ;ghosts' at low relative centrifugal forces. Omission of either Krebs-Ringer phosphate or dextran from the medium resulted in almost complete cell breakage during the homogenization. 5. The isolated cell ;ghosts' were used as a starting material for subcellular fractionation of rat intestinal mucosa by differential centrifugation. The distributions of protein and succinate-dehydrogenase activity among the fractions were compared with corresponding values in fractions isolated by differential centrifugation of mucosa homogenized in 0.3m-sucrose-5mm-EDTA, pH7.4. The method in which cell ;ghosts' were used as starting material gave a better separation and cleaner fractions than the method in which untreated mucosal scrapings were used.

Acid Phosphatase↗