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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. A method of measuring the permeability of the pancreas by determining the apparent reflexion coefficient (sigmaA) is described, in the isolated pancreas secreting maximally under the influence of secretin. The principle is to add a non-electrolyte to the perfusate which will create an osmotic gradient (RTsigmadeltaC) counter to that of active transport and reduce the secretion rate. This is compared with the effect of an equal concentration (0.1 M) of sucrose (RTdeltaC; sigma = 1). The apparent reflection coefficient is obtained by dividing the percentage reduction in the secretion rate due to the test molecule with that due to sucrose. 2. Sucrose when added to the perfusate inhibits pancreatic secretion. For every 10 mM increase in sucrose concentration, the secretion rate was inhibited by 7.1%. It has been estimated that an osmotic gradient of 131 m-osmole/kg water will cause zero flow rate. This is a measure of the pressure required to counteract the local osmotic gradient set up by active transport, it is equivalent to about 3.4 atm. 3. Non-electrolytes with molecular volumes greater than about 85 cm3 mole-1 are relatively impermeable, below this value they enter the pancreatic juice with increasing ease as the molecular volume decreases. 4. SigmaA for a number of compounds has been measured: urea 0.17; ethanediol 0.27; thiourea 0.51; glycerol 0.69; creatinine 0.81; erythritol 0.91; arabinose 0.96; xylose 0.98; sorbitol 0.98. 5. The addition of non-electrolytes to the perfusate had effects on pancreatic secretion which were a function of sigmaA. For molecules with sigmaA lying between 0.81 and 1.0 an osmotic load of 0.1 M increased both the concentration of sodium plus potassium and the concentration of chloride plus bicarbonate by about 50 m-mole/l. Whereas the cation change is almost exclusively one of sodium that of the anions was preferentially an increase in chloride. For compounds with sigmaA lying between 0 and 0.81 the concentration of sodium plus potassium was proportional to sigmaA. 6. A number of compounds have been described which inhibit pancreatic secretion, other than by an osmotic effect. These include acetaldehyde, thioglycerol, nicotinamide, ribose, dihydroxyacetone, and glyceraldehyde. 7. It is concluded that the pancreas is more permeable than the gall-bladder of rabbit, fish and bullfrog, the proximal tubule of the kidney of rat and the small intestine of bullfrog, but is probably similar to that of small intestine of guinea-pig and man.
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PMID:The permeability of the secretin stimulated exocrine pancreas to non-electrolytes. 65 May 9

The kinetics of initial cholesterol uptake by everted rat proximal and distal small intestinal sacs were evaluated in vitro. The mucosal incubation solution consisted of 0.05 mM cholesterol solubilized in 4.8 mM sodium taurocholate micellar solution at pH 7.4 Experiments were performed at temperatures from 26 to 38 C. The rate of cholesterol uptake followed a linear relationship when plotted against time indicating an apparent zero-order kinetics mechanism for initial uptake. An Arrhenius plot of the results of uptake versus temperature remained linear over the entire range of temperatures studied. The large free energy of activation (20 kcal/mole) suggests that an energy barrier for cholesterol uptake exists at the enterocyte luminal cell membrane and may be an important limiting step in cholesterol uptake. It is proposed that a transient association between cholesterol and a component of the enterocyte luminal cell membrane is formed during initial uptake of cholesterol. The transient association may be an activated complex formed with proteins present at or within the luminal enterocyte cell membrane.
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PMID:Initial cholesterol uptake by everted sacs of rat small intestine: kinetic and thermodynamic aspects. 66 8

Several lines of evidence indicate that ligandin consists of two different subunits. The protein dissociates into two components that are detected by electrophoresis in a discontinuous sodium dodecyl sulfate system, or in acid-urea gels, and by isoelectric focusing in the presence of urea. The apparent molecular weights of the two polypeptides are 25,000 and 22,000. Alkylated or succinylated ligandins also exhibit subunit heterogeneity and resolved into two bands in these electrophoretic systems. Cross-linked ligandin showed only one band in sodium dodecyl sulfate-gel electrophoresis indicating that the two subunits are part of a heterodimeric protein rather than monomers of two different proteins. No dansylated terminal amino acids were detected suggesting that the NH2-terminal residues of both chains are blocked. One mole of arginine or phenylalanine was released per mole of ligandin after digestion with carboxypeptidase B or A, respectively. Tryptic maps of succinylated ligandin were consistent with identical disposition of arginine residues in both chains, but several additional tryptic peptides were obtained with native ligandin as compared to the predicted number if both subunits were identical. These observations are consistent with the possibility that both subunits contain common sequences and that a small peptide of about 25 to 30 amino acid residues is cleaved from the COOH-terminal of the larger subunit to produce the smaller subunit.
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PMID:Studies on subunit structure and evidence that ligandin is a heterodimer. 66 96

1. Changes in the water and ion contents of rabbit renal cortical slices, which had been bathed, immediately after slicing, in air-equilibrated media at room temperature ('freshly prepared slices'), were followed during subsequent incubation at 25 degrees C in oxygenated media of the same composition as the initial bathing medium. 2. In comparison with conventional 'equilibrated' slices (slices incubated at 25 degrees C in oxygenated ordinary medium immediately after slicing) these 'freshly prepared' slices had increased tissue water, sodium and chloride contents and low tissue potassium contents. 3. Control freshly prepared slices incubated at 25 degrees C in oxygenated ordinary medium recovered within 4 min to the tissue water content that is usual for rabbit renal cortical slices incubated in oxygenated ordinary medium at 25 degrees C. Freshly prepared slices incubated at 25 degrees C in oxygenated media containing 1 mM-oubain took 75 min or more to recover to this usual tissue water content. Thus the presence of 1 mM-oubain in both bathing and incubation media produced a marked inhibition of the volume recovery observed when freshly prepared slices are incubated in oxygenated media at 25 degrees C. 4. Reduction of the ouabain concentration reduced the inhibition of cell volume recovery. 5. Replacement of medium glucose by 3-O-methylglucose did not inhibit cell volume recovery in the absence of ouabain. 6. The oxygen consumptions of slices that were bathed and incubated in 1 mM-ouabain media were similar to those of slices initially bathed and incubated in ouabain-free media and then incubated in ouabain media. Thus the effect of ouabain in inhibiting cell volume recovery was unlikely to be secondary to inhibition of cellular energy production. 7. The tissue potassium content of slices incubated aerobically in 1 or 10 mM ouabin fell to an apparently stable value of approximately 100 m-mole/kg dry wt., which corresponds to a calculated concentration ratio of 10:1 across the cellular membrane, suggesting that some residual potassium uptake may still have been occurring. 8. These results indicate that in freshly prepared rabbit renal cortical slices ouabain-sensitive mechanisms play a major role in cell volume recovery. They are not in accord with the postulate that renal cortical cells possess a separate ouabain-insensitive mechanism regulating cell volume.
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PMID:Ouabain and regulation of cellular volume in freshly prepared slices of rabbit renal cortex. 67 54

Bicarbonate appearance in the lumen and its relationship to solute absorption were studied in a Pavlov pouch in the cardiac region of the first compartment of the llama forestomach. HCO3- appearance showed no diurnal variation. HCO3- accumulation was highly dependent on the pH of the solution used. The HCO3- ion probably is formed from CO2 diffusing into the lumen from the serosal side, as a result of cell metabolism and of OH- ions. HCO3- accumulation was closely related to volatile fatty acid (VFA) absorption. The ratio of HCO3- appearance to VFA absorption depended on the pH of the solution. At a pH of 6.6, about 0.1 mol HCO3- and, at a pH of 7.8, 0.9 mol HCO3- appeared per mole absorbed VFA, indicating that at slightly alkaline pH nearly all H+ ions required for the nonionic absorption of VFA appeared to be delivered from the dissociation of H2CO3. Bicarbonate gain and VFA absorption were increased when animals were not fed for 48 h. Sodium absorption was related to VFA as well as water absorption.
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PMID:Bicarbonate secretion and solute absorption in forestomach of the llama. 67 5

Isolated snail ganglia are capable of maintaining their free amino acid levels steady for the first 60 min of incubation in physiological saline. Within this time the ganglia also possess an uptake mechanism for DL-glutamate which can be divided into sodium-sensitive and -insensitive components. The accumulation of DL-glutamate showed saturation kinetics typical of a carrier-mediated process. The Vmax value for the uptake is 1.5 x 10(-8) mole/g/min and the Km value 1.1 x 10(-4) M. The amino acid accumulation is quite specific towards L-dicarboxylic acids and insensitive to a number of metabolic inhibitors. It is unlikely to be due to a homoexchange phenomenon because the ganglia are capable of achieving a net uptake of glutamate and the efflux of DL-[3H]glutamate is not increased by the addition of non-radioactive L-glutamate to the incubation medium.
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PMID:The accumulation of DL-glutamate by the central nervous system of the snail Helix pomatia. 68 72

Mitochondrial glycerol-3-P dehydrogenase (EC 1.1.99.5) has been purified in 20% yield from both rabbit skeletal muscle and brain using a four step procedure involving osmotic shock, solubilization with Triton X-100, hydrophobic chromatography, gel filtration, and preparative column isoelectrofocusing. The active muscle and brain enzymes were found to be 95% and 80% homogeneous, respectively. Final purification was performed on the denatured subunit. The active enzyme from each of the tissues focused at pH 5.25 +/- 0.12 and each produced similar biphasic thermal inactivation plots at 50 degrees C. Mixtures of the purified brain and muscle enzymes co-migrated in discontinuous electrophoresis gels and each enzyme exhibited a single polypeptide component on sodium dodecyl sulfate (SDS) gels either when run separately or in mixtures. The subunit molecular weight was shown to be 76,000 +/- 3,000 by SDS-gel electrophoresis and gel filtration in 6 M guanidine HCl. One mole of noncovalently bound FAD and 1 mole of iron were measured per Mr = 100,000. The amino acid composition was determined based on the assumption of 70 aspartate residues per subunit to give a Mr = 76,000. The absorption spectrum has a maximum at 416 nm and a shoulder at 450 to 460 nm which is bleached on treatment with sodium dithionite. The maximum at 416 nm is removed by treatment with mersalyl.
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PMID:Isolation and characterization of flavin-linked glycerol-3-phosphate dehydrogenase from rabbit skeletal muscle mitochondria and comparison with the enzyme from rabbit brain. 70 Dec 95

Agarase was concentrated and purified from culture filtrates of an agar-degrading Pseudomonas-like bacteria by affinity chromatography on divinyl sulphone cross-linked Sepharose 4B. By fractionation on Sephadex G-200 three fractions were obtained two of which, agarases I and II, had agarase activity. Agarase II was further purified by isoelectric focusing, and the main peak, agarase IIb, was isoelectric at pH 5.1. Molecular weight determinations indicated agarase I to be a dimer with Mr approximately 210 000. The Mr of agarase IIb was 63 000 as determined by analytical ultra-centrifugation, polyacrylamide gel electrophoresis in sodium dodecyl sulphate and molecular sieve chromatography on Sepharose 4B in 6M Gdn-HCl. The amino acid compositions of the two proteins were very similar and both were found to be glycoproteins. The pH optimum of the enzymes was 6.7 and the optimal temperature was 38 degree C for agarase I and 43 degree C for agarase IIb. Melted agarose and agarose gel were used as substrates for the enzymes. The ratio of the activities towards the different substrates was 4.3 for agarase I and 1.0 for agarase IIb. Agarase I hydrolyzed the beta-linkages in neoagarooctaose so as to produce two moles of neoagarotetraose or one mole of neoagarohexaose and one mole of neoagarobiose. Agarase IIb hydrolyzed only the central beta-linkage to form two moles of neoagarotetraose.
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PMID:Purification and characterization of two different agarose-degrading enzymes. 71 80

1. The intracellular Na activity, aiNa, of sheep heart Purkinje fibres was continuously monitored using Na+-sensitive glass micro-electrodes. The effects of removal and restoration of external K, and of application and removal of various cardioactive steroids, were investigated. 2. The aiNa increased in K-free solutions and rapidly recovered on addition of external K. The rate of this recovery depended on both the external K concentration, [K]o, and the aiNa. The rate of aiNa recovery was found to be half maximally activated at a [K]o of about 10 mM. If corrections are applied to allow for changes in the net passive Na influx at various [K]o, then this value is increased to approximately 12.5 mM. 3. At a given [K]o, there appeared to be a linear relationship between the rate of aiNa recovery and the level to which aiNa had increased in K-free solution (over the range of aiNa from 7.5 to 31 mM). 4. Addition of the cardioactive steroids strophanthidin, acetylstrophanthidin, actodigin (AY 22,241) or dihydro-ouabain produced rapid changes of aiNa. At low concentrations, these compounds sometimes produced a small decrease in aiNa, while at concentrations above 10(-7) M they produced a dose-dependent increase. 5. The effects on aiNa of both low and high concentrations of all these cardioactive steroids were readily reversible within 120 min. The time course of the aiNa recovery mainly depended on the concentration of the cardioactive steroid applied, and on the level to which aiNa had increased. 6. Upon addition of a cardioactive steroid (above 10(-7) M, aiNa at first increased almost linearly with time. The rates of such an increase were measured during this period at various cardioactive steroid concentrations and used to produce dose-response curves. The concentrations that produced a half-maximum rate of aiNa increase were near to 10(-6) M for strophanthidin and acetylstrophanthidin, but near to 10(-5) M for actodigin and dihydro-ouabain. 7. The mean maximum rate of aiNa increase produced by the addition of a high cardioactive steroid concentration was 0.49 +/- 0.17 mM/min (+/-S.D., n = 21). This would indicate a net passive Na influx into the cells of approximately 2.8 p-mole/cm2sec. 8. This maximum rate of aiNa increase could be achieved by the addition of 10(-5) M-strophanthidin or acetylstrophanthidin, but 10(-4) to 10(-3) M-actodigin or dihydro-ouabain was required to produce a similar rate of increase. 9. The addition of these high cardioactive steroid concentrations produced an initially rapid increase of aiNa. After 15-30 min this aiNa increase slowed considerably. The aiNa appeared to reach a 'plateau' within 2-4 hr at levels much below those predicted for a Na electrochemical equilibrium across the cell membrane.
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PMID:The intracellular sodium activity of cardiac Purkinje fibres during inhibition and re-activation of the Na-K pump. 73 36

Active sodium transport is classically analyzed in terms of an equivalent circuit, comprising an active conductance Ka and an electromotive force of sodium transport ENa. Although ENa is commonly considered the driving force of transport, model experiments have suggested that ENa is a composite parameter, incorporating both kinetic and energetic factors. An alternative approach considers both transport and the associated oxidative metabolism in terms of a nonequilibrium thermodynamic (NET) formulation, involving phenomenological coefficients and the affinity A, presumed to represent kinetic and energetic factors, respectively. Model experiments testing the NET formulation suggest that the affinity is indeed an energetic parameter. Calculated values of A in untreated frog skins and toad bladders range from about 20 to 80 kcal per mole of O2 consumption. Assuming a P/O ratio of 3, this range corresponds to about 3--13 kcal per mole of ATP utilization, values compatible with reported direct measurements. Although brief perturbations of transepithelial electrical potential deltapsi resulted in linear current-voltage relationship, indicating constancy of ENa and Ka, 15-min perturbations of deltapsi resulted in nonlinearity, indicating changes in ENa and Ka; perturbations of deltapsi enhancing active transport were associated with decrease of ENa and increase of Ka; slowing of active transport produced the converse effects.
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PMID:Evaluation of kinetic and energetic parameters of active sodium transport. 73 76


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