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Biomedical subjects

D Chapman

Publications and source records attributed to D Chapman.

At least 271 records · Page 15Linked to original sources
PubMed1977

Na+ transport in jejunal crypt cells.

As enterocytes migrate from crypts to villi they differentiate and mature. To examine the effect of epithelial differentiation on ion transport we studied 22Na+ efflux and (Na+--K+)-adenosine triphosphatase activity in suspensions of epithelial cells selectively isolated from different regions of the villus to compare crypt cells with villous tip cells. Enterocytes were isolated from rat jejunum by a dilation-vibration technique. Thymidine kinase, sucrase, and alkaline phosphatase activities were measured as markers of specific cell populations. Compared to villous cells, cells from the crypt region demonstrated lower (Na"--K+)-adenosine triphosphatase activity, lower total and passive Na+ efflux rate constants, and failure of Na+ transport to respond to an actively transported nonelectrolyte.

Adenosine Triphosphatases↗
PubMed1976

Phospholipid phase transitions. Effects of n-alcohols, n-monocarboxylic acids, phenylalkyl alcohols and quaternary ammonium compounds.

The interactions of a series of alcohols, acids and quaternary ammonium salts with a phosphatidylcholine-water model biomembrane (dipalmitoyl phosphatidycholine) system have been studied using differential scanning calorimetry. In particular the effects of these molecules upon the lipid endothermic phase transitions were investigated over a range of concentrations. A variety of effects was observed. (a) Those molecules which shift or broaden the main lipid transition can also remove the pretransition endotherm. (b) n-Alcohols and n-monocarboxylic acids containing the same number of carbon atoms have very similar effects at molar concentrations up to 40%. Those molecules containing 12 or more carbon atoms raise the main lipid phase transition whilst those molecules containing 10 or less carbon atoms lower this transition temperature. (c) The phase diagram of stearoyl alcohol in the phosphatidylcholine-water system shows the formation of lipid-alcohol complexes. (d) Alkyl trimethyl ammonium bromides showed behaviour which differs considerably from n-alcohols and n-carboxylic acids of the same chain length. (e) Other alkyltrialkyl and tetraalkylammonium bromides show that a variety of effects on the lipid phase transition can be obtained. (f) With the homologous series of phenyl-alkyl alcohols from benzyl alcohol to 4-phenyl butanol increasing the number of methylenes between the terminal OH and the benzene ring leads to greater interaction between solute and bilayer. The range of different effects obtained with the compounds studied offers a means for introducing various degrees and types of perturbation into membrane systems.

Alcohols↗
PubMed1976

Sodium ion transport in isolated intestinal epithelial cells. II. Comparison of the effect of actively transported sugars on sodium ion efflux in cells isolated from jejunum and ileum.

Na+ transport studies in intestinal epithelial cells indicate that enterocytes from different regions of the small intestine differ in their response to actively transported sugars. 1. Compared with sugar-free medium total Na+ efflux rate constants from isolated rat jejunal cells were significantly increased when medium contained actively transported sugars, glucose and galactose, but not when medium contained fructose. 2 In contrast total Na+ efflux rate constants from isolated rat ileal cells did not respond to actively transported sugars, glucose and galactose. 3. Similar results for the effect of actively transported sugars on Na+ ellux were obtained for isolated rabbit jejunal and ileal epithelial cells. 4. Passive Na+ efflux rate constants for isolated jejunal and ileal enterocytes are not significantly different, indicating similiar permeability characteristics.

Animals↗
PubMed1976

A method for the modulation of membrane fluidity: homogeneous catalytic hydrogenation of phospholipids and phospholipids and phospholipid-water model biomembranes.

The fatty acids associated with phospholipids of cell membranes, and particularly their degree of unsaturation, contribute to the fluidity of their structure and hance determine many of their biological properties. We describe a technique for modulating membrane fluidity which consists of hydrogenating the unsaturated double bonds of membrane phospholipids. This has been accomplished using a homogeneous catalyst. The process has been applied to phospholipids in organic solvents, to phospholipids dispersed as multibilayers in aqueous systems, and also to sonicated preparations of phospholipids arranged as single bilayer vesicles. Preliminary experiments have also been performed with biological membranes. These results indicate that the process of homogeneous catalysis for the modulation of lipid fluidity of biological cell membranes may have considerable future biological and biochemical application.

Catalysis↗
PubMed1975

On GABA metabolism in the gliocyte cells of the rat pineal gland.

The uptake of the inhibitory transmitter substance gamma-aminobutyric acid (GABA) into the adult rat pineal gland was studied autoradiographically using both light and electron microscopy. The sites of GABA uptake were shown to be exclusively present in the gliocyte cells of the gland following both in vitro incubation with tritiated GABA and after in vivo administration of the amino acid by intra-arterial injection. Both the pinealocyte cells and the numerous sympathetic axons in the gland were devoid of silver grains. Preliminary biochemical studies indicated that the gliocyte uptake process for GABA resembles that in the satellite glia of the sensory ganglia but differed from that in slices of the cerebral cortex. Evidence is also presented which shows the pineal gland to contain endogenous GABA and the enzymes directly associated with its in vivo metabolism, L-glutamate-1-carboxylase (EC 4.1.1.15) (GAD) and GABA-2-oxoglutarate aminotransferase (EC 2.6.1.19) (GABA-T). Furthermore, a 3-fold rise in endogenous GABA occurred in the pineal after inhibition of GABA-catabolism as would be expected if the GABA-shunt pathway was functionally active in the oxidative metabolism of the pineal gland.

Aminobutyrates↗
PubMed1975

Tilted hydrocarbon chains of dipalmitoyl lecithin become perpendicular to the bilayer before melting.

Differential scanning calorimetry studies of dipalmitoyl lecithin show two reversible transitions as the temperature is changed between 20 and 50 degrees C. A pretransition endotherm occurs at 35 degrees C prior to the main chain melting endotherm which occurs at 42 degrees C. X-ray diffraction studies show that below 33 degrees C the chains of the lecithin are fully extended, packed in a hexagonal crystalline lattice but tilted with respect to the plane of the bilayer. Between 35 and 42 degrees C the chains are similarly packed but oriented perpendicular to the bilayer plane. Above 44 degrees C the chains are "melted" or disordered. Monolayer studies of dipalmitoyl lecithin using continuous recording of pressure with molecular area reveal the existence of two solid condensed phases corresponding to these tilted and verticle chain structures. The tilted to perpendicular transition would account for the pretransition endotherm of the lipid; the crystalline to melted change corresponds to the larger transition observed at 42 degrees C.

Calorimetry↗
PubMed1974

Biological membranes.

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Biological Transport, Active↗