Biomedical subjects

C Enrich

Publications and source records attributed to C Enrich.

61 records · Page 4Linked to original sources

PubMed1986

[Changes in sialic acid content of the plasma membrane in hepatocellular proliferation].

The content of sialic acid bound to the sinusoidal region of plasma membrane during the prereplicative phase after the intravenous injection of a solution containing triiodothyronine, amino acids, glucagon and heparin (T.A.G.H. solution) has been measured. The results obtained show that an important decrease in sialic acid content is produced as it occurs in the hepatic cells of hepatectomized animals. In order to know if sialidase activity is involved in the decrease of sialic acid content during liver regeneration, the activity of sinusoidal plasma membrane sialidases during the prereplicative phase after the partial hepatectomy has been studied. No modifications of sialidase activity were detected during this period of time indicating that this decrease in sialic acid content has to be produced by other mechanisms such as diminution in the synthesis of precursor molecules. On the other hand due to the importance of Ca2+-calmodulin complexes in the activation of the hepatic cell proliferation the possible implication of this complex on the loss of sialic acid, observing the effect of trifluoperazine (inhibitor of Ca2+-calmodulin complexes) during the prereplicative phase of liver regeneration has been studied. The results show a delay in the decrease of the amount of sugar studied from 10 to 12 hours compared to the results obtained with the hepatectomized rats that have not received trifluoperazine.

Animals↗

PubMed1985

Characterization of plasma-membrane glycoproteins from functional domains of the rat hepatocyte.

Plasma-membrane glycoproteins from the three different functional domains of the rat hepatocyte were radioactively labelled by oxidation with NaIO4, followed by reduction with NaB3H4. Analysis of the radioactively labelled glycoproteins by polyacrylamide-gel electrophoresis revealed the presence of at least 12 major sialoglycoproteins in each different region of the hepatocyte surface. The Mr-110 000 component was homogeneously distributed over the plasma membrane, whereas the Mr-90 000 polypeptide was only located at the sinusoidal face. These radiolabelled glycoproteins were solubilized in 1% Triton X-100, and the soluble fraction was subjected to affinity chromatography on Sepharose-conjugated wheat-germ agglutinin (WGA). The labelled glycoproteins were poorly bound to WGA. Membrane glycoproteins were also labelled by the galactose oxidase/NaB3H4 method. The results show that the polypeptides with apparent Mr 170 000 from the sinusoidal, 230 000 from the canalicular and 170 000 from the lateral membranes were specifically labelled. When the membranes were treated with neuraminidase and galactose oxidase/NaB3H4, the electrophoretic patterns showed changes in the apparent Mr values of the glycoproteins, owing to loss of sialic acid, and a clear increase in labelling in the sinusoidal and canalicular membranes compared with the lateral membranes. When these labelled membranes were solubilized in 1% Triton X-100 and subjected to affinity chromatography on Sepharose-conjugated Ricinus communis agglutinin and/or Lens culinaris agglutinin, the results showed that the former columns efficiently bound the radiolabelled glycoproteins, whereas the latter columns bound poorly. The results show that there is a differential distribution of glycoproteins along the hepatocyte's surface.

Animals↗

PubMed1985

Pre-replicative changes of the rat sinusoidal plasma membrane glycoproteins during hepatic regeneration.

Cell-surface glycoproteins of rat liver sinusoidal plasma membranes from control and regenerating livers were studied. The glycoproteins were labeled using specific methods for sialic acid (NAIO4/NaB3H4) and galactosyl/N-acetyl galactosaminyl residues (galactose oxidase/NaB3H4 and neuraminidase-galactose oxidase (NaB3H4) and the solubilized proteins were analyzed by gel electrophoresis. The patterns obtained with regenerating livers were quantitatively different from controls. This shows that cell surface glycoproteins change during liver regeneration.

Adenosine Triphosphatases↗

PubMed1985

Induction of plasma membrane alkaline phosphatase in rat liver.

We have determined alkaline phosphatase activity in total liver plasma membrane fractions from rats subjected to a partial hepatectomy and sham operated with or without manipulation of the liver. In all these cases, an increase of the enzyme activity was observed. Kinetic studies of alkaline phosphatase activity performed on plasma membrane fractions from rats subjected to a partial hepatectomy suggest that alkaline phosphatase increase is produced by de novo biosynthesis of enzyme molecules. Determination of alkaline phosphatase activity in purified plasma membrane subfractions corresponding to each of the three functional regions of the hepatocyte surface (blood sinusoidal, lateral and bile canalicular), indicates that the increase of the enzyme activity observed after partial hepatectomy is selectively induced in the bile canalicular domain of the hepatocyte plasma membrane.

Alkaline Phosphatase↗

PubMed1985

Effect of trifluoperazine on DNA synthesis during liver regeneration.

An intraperitoneal injection of the calcium-calmodulin blocker trifluoperazine into rats at 4 hr after a partial hepatectomy produced a strong inhibition of DNA synthesis observed at 24 hr after surgery; but when injection was administered at 20 hr after hepatectomy, it did not produce any effect on DNA replication. These observations indicate that trifluoperazine acted by blocking one or more events involved in triggering DNA replication but it did not affect on-going DNA synthesis. A more detailed study indicated that when trifluoperazine was injected at 4 hr after surgery, a 12 hr delay in the cytosolic calmodulin surge observed between 6 and 12 hr after partial hepatectomy (previous to initiation of DNA replication) and also in the starting of DNA synthesis was produced. These findings suggest that the pre-replicative surge of cytosolic calmodulin could be involved in triggering DNA synthesis observed after partial hepatectomy.

Animals↗

PubMed1984

Quantitative and qualitative changes of plasma membrane glycoproteins in the early period of liver regeneration.

Alterations of cell surface glycoconjugates have been observed in many developing systems and may be important in the physiological control of growth and differentiation. Liver regeneration after partial hepatectomy is a suitable model in which to study the regulatory mechanisms of cell proliferation in vivo. We have isolated the sinusoidal plasma membrane of hepatocytes at different times after partial hepatectomy. The sialic acid content and the SDS-polyacrylamide gel electrophoresis pattern of glycoproteins were determined. A decrease of periodic acid-Schiff-profiles, a change in the binding capacities of 125I-concanavalin A, a reduction of the sialic acid content and the appearance and disappearance of specific components have been observed during the pre-replicative phase of liver regeneration. These findings during this early period are consistent with the active involvement of the plasma membrane glycoproteins in the transition of cells to the proliferative state.

Animals↗

PubMed1983

Cerebral subcellular distribution of CDP-choline and/or its metabolites after oral administration of methyl-14C CDP-choline.

Distribution of radioactivity in subcellular components of a cerebral extract after oral administration of methyl-14C labelled cytidine diphosphate choline (CDP-choline, citicoline, Somazina) was analyzed. Animals were decapitated 24 h after the administration and the brain immediately removed and gently homogenized in a buffer solution. The homogenate was fractionated by differential centrifugation and the protein concentration and the radioactivity were measured in each precipitate as well as in the final supernatant. Radioactivity was found to be associated mainly with membranous microsomal precipitate and with cytoplasmic membrane precipitate. Alternatively, materials sedimenting between 500 X g and 20,000 X g were fractionated in a density gradient centrifugation. Fractions were screened for enzymatic activities as indicators of cytoplasmic membrane, mitochondria, lysosomes, microsomes and synaptosomes. Radioactivity was found to be associated with cytoplasmic and microsomal membrane fractions. Identification of some fractions as enriched in synaptosomes also accumulating radioactivity, as well as the possible incorporation of the radioactivity to choline and phosphorylcholine cerebral pools are discussed.

Administration, Oral↗