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Biomedical subjects

R B Fisher

Publications and source records attributed to R B Fisher.

At least 37 records · Page 2Linked to original sources
PubMed1980

Active intestinal transport of methyl red isomers.

Transport across the wall of rat jejunum of two isomers of methyl red has been studied. These isomers, meta-methyl red (MMR) and para-methyl red (PMR), are absorbed against a concentration gradient. Uptake consists of three components: rapid adsorption on to the mucosa, a steady uptake proportional to lumen concentration and a reflux which increases exponentially to a limiting value. A substantial part of the uptake is stored in the mucosa, and some of it is metabolized to colourless derivatives. If methyl red is washed out of the lumen after the mucosa has been loaded, there is some reflux into the lumen, but most of the stored methyl red passses into the secretion. The rate of this transport on to the serosal surface is not noticeably diminished until the adverse concentration gradient exceeds 13-14:1. Once the methyl red has been washed out of the lumen there is no further metabolism of methyl red to colourless derivatives. Shifting the lumen pH from 7.4 to 6.4 whilst keeping the tissue fluid pH constant increases the rate of uptake from the lumen by a factor of only 1.68 although the concentration of unionized methyl red is increased approximately 10-fold. It seems that at pH 7.4 about 90% of the uptake is of the ionized form, and that at pH 6.4 this percentage falls to 50. It is concluded that the methyl reds form fresh examples of foreign organic compounds which can be transported actively by the small intestine and that they can be taken up from the lumen into the mucosa in both ionized and unionized states.

Animals↗
PubMed1979

The breakdown of 2,3-bis(phospho)-D-glycerate by Fe(III)-haemoglobin.

Fe(III)-haemoglobin is shown to catalyse the hydrolysis of 2,3-bis(phospho)-D-glycerate to Pi and 3-phosphoglycerate, although the rate is slow, even when the protein is present at concentrations in the millimolar range. The rate of hydrolysis is proportional to the subtrate concentration up to at least 10 mM, so if the process is enzymic, the Km must be high.

Diphosphoglyceric Acids↗
PubMed1976

A diurnal rhythm in the absorption of glucose and water by isolated rat small intestine.

1. Glucose and water absorption by isolated small intestine from rats which have had unrestricted access to food is 50-60% higher at night than during the daytime. 2. When the feeding time is restricted to 06.00-09.00 hr G.M.T. glucose and water absorption rates in the period from 3 to 7 hr after withdrawal of food are almost as high as the rates observed at night-time in the animals with unrestricted feeding. 3. These changes in absorption rates appear to be associated with feeding time and not with the pattern of illumination.

Animals↗
PubMed1975

Transport of deutherium oxide across isolated rat small intestine.

1. Transport of deuterium oxide from a luminal perfusate containing 1% D2O was studied in Fisher & Gardners (1974) isolated preparation of perfused rat small intestine. 2. The kinetics of appearance of D2O in the intestinal secretion at the serosal surface fitted well to a single exponential function. 3. The steady-state concentration of D2O in this secretion was not significantly different from the concentration in the luminal perfusate. 4. The total tissue water contained D2O at a concentration, on average, 5% lower than that in the luminal perfusate. 5. There is no evidence to suggest discrimination in transport across the intestinal mucosa between H2O and D2O. 6. The kinetics of wash-in of D2O to intestinal secretion show that the ratio of flux out of the lumen to reflux back to the lumen is 1-38;1.

Animals↗
PubMed1974

A kinetic approach to the study of absorption of solutes by isolated perfused small intestine.

1. A new technique has been developed for making serial measurements of water and solute absorption from the lumen of isolated small intestine.2. The isolated intestine is perfused in a single pass with a segmented flow of slugs of liquid separated by bubbles of oxygen-carbon dioxide mixture. Simultaneous collections are made of effluent from the lumen and of the fluid which is transported across the mucosa. This latter fluid appears to be a fair sample of the tissue fluid.3. Conditions in the lumen can be changed within less than 5 min. The effects of two or more treatments applied to the same segment of intestine can be determined and the time course of a change in luminal conditions.4. The rate of appearance of solutes on the serosal side depends on the rate of water absorption, and changes exponentially towards a steady state. The rate constant is a function of tissue fluid volume.5. In the steady state the concentration of glucose in the tissue fluid is 71 mM when the luminal concentration is 28 mM, and is 45 mM when the luminal concentration is 8.3 mM.6. For solutes such as glucose for which reflux from tissue fluid to lumen is small relative to flux from lumen to tissue fluid, the time of attainment of a steady state in secretion is usually 50-60 min.7. For solutes such as sodium for which the reflux is relatively high, the steady state may be reached in 15-20 min.8. The K(m) for glucose absorption (14-19 mM) is much lower than is found with unsegmented flow perfusion.9. These findings emphasize problems in interpreting results from other types of intestinal preparation.10. The rate of glucose absorption from the lumen falls only gradually when the luminal sodium concentration is reduced abruptly. In contrast the rate of glucose absorption falls suddenly when the luminal glucose concentration is reduced abruptly. This suggests that glucose absorption is not directly dependent on luminal sodium ions.

Animals↗
PubMed1974

Dependence of intestinal glucose absorption on sodium, studied with a new arterial infusion technique.

1. A new preparation of isolated rat jejunum plus ileum (ca. 100 cm) is described in which a saline infusate is pumped into the superior mesenteric artery, the superior mesenteric vein having been ligated.2. The arterial infusate washes out the tissue spaces: the lumen is perfused in a single pass with a segmented flow as by Fisher & Gardner (1974).3. At an arterial infusion rate of 3 ml./min, steady states are set up in the tissue fluid within 10-15 min: the compositions of the fluids bathing both sides of the mucosa can therefore be controlled.4. The rate of glucose absorption from the lumen falls only gradually when the luminal sodium is replaced by choline abruptly while the tissue fluid sodium is maintained at 144 m-equiv/l. by arterial infusion.5. The rate of glucose absorption from the lumen is unaffected by replacement of sodium in the arterial infusate by choline.6. Ouabain (10(-4) M) in an arterial infusate containing sodium 144 m-equiv/l. causes inhibition of glucose and water absorption from the lumen. There is no effect of ouabain when the arterial infusate contains sodium, 0 or 72 m-equiv/l.7. Arterial ouabain does not reverse the effects of depletion of luminal sodium. Simultaneous removal of luminal sodium and application of arterial ouabain causes faster inhibition of glucose absorption than does either treatment alone.8. Glucose absorption is more likely to depend on rate of efflux of sodium from mucosal cell to tissue fluid than on a sodium gradient at the brush border or on intracellular sodium concentration.

Animals↗
PubMed1970

Accessibility of heart water to pentoses.

1. The raffinose space, the inulin space and the weight loss on compression of perfused rat hearts are indistinguishable in magnitude.2. The inulin space shows systematic variations from day to day and is also affected by the procedure used for removing surplus water from the perfused heart. It is therefore not safe to use a mean figure of extracellular space in permeability experiments.3. Perfusion of hearts with arabinose solutions alters the intracellular water content. These alterations can be accounted for if it is assumed that the arabinose which penetrates the cells is uniformly distributed in the cell water.4. By appropriate choice of pentose concentration and of time of perfusion it can be shown that all the estimated cell water is accessible to pentose.5. It is concluded that no detectable fraction of the extracellular water is inaccessible to inulin and that no detectable fraction of the intracellular water is inaccessible to pentose.

Animals↗
PubMed1970

Kinetics of pentose permeation in the perfused rat heart.

1. The fractional permeation of heart cell water by L-arabinose and D-xylose after a standard period of perfusion is less the higher the extracellular pentose concentration.2. At any given pentose concentration the kinetics of permeation are consistent with passive diffusion through the cytoplasm or with transport across the cell membrane by a saturable carrier.3. The concentration dependence of permeation is inconsistent with passive diffusion.4. The kinetics of L-arabinose permeation are consistent with a carrier having V(max) = 2.2 m-mole/l. extracellular water per min and a half-saturation concentration [K] of 0.5 x 10(-4)M. The corresponding figures for D-xylose are V(max) = 1.4, [K] = 1.6 x 10(-4)M.

Animals↗
PubMed1970

The effect of insulin on the kinetics of pentose permeation of the rat heart.

1. The kinetics of permeation of pentoses into the rat heart in the presence of insulin are similar in nature to those in the absence of insulin.2. The half-saturation concentration of the carrier system is increased by insulin in a manner which is independent of insulin concentration.3. The V(max) of the carrier system is altered by insulin in a graded fashion: at low insulin concentrations it may be lower than in the absence of insulin.4. It is shown that these effects can be accounted for if insulin combines with the carrier and thereby increases either the rate constant governing the mobility of the carrier in the membrane or the rate constant governing dissociation of the sugar-carrier complex.5. The effects cannot be accounted for by a graded action of insulin on the membrane as distinct from the carrier.

Animals↗