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C A Barth

Publications and source records attributed to C A Barth.

47 records · Page 3Linked to original sources
PubMed1982

Transcellular transport of fluorescein in hepatocyte monolayers: evidence for functional polarity of cells in culture.

The rat liver in vivo transfers bile salts, proteins, and dyes from blood into bile. It is the purpose of this communication to demonstrate the maintenance of this transcellular transport in cultured adult rat hepatocytes. Two minutes after adding fluorescein (20 microgram/ml) to the culture medium, maximal cellular fluorescence was observed through the fluorescence microscope. Subsequently, intercellular clefts showed a steadily increasing fluorescence with a maximum between 5 and 20 min, resulting in a brightly fluorescent network of intercellular gaps. The following observations are taken as evidence that these findings reflect cellular uptake and canalicular secretion of the dye. First, the same sequence of observations was made upon addition of fluorescein diacetate (a nonfluorescent precursor of fluorescein), proving that the compound had been taken up and metabolized in the cells to fluorescein before secretion into intercellular clefts. Second, preincubation of the monolayers with the cholestatic bile salt taurolithocholate (100 mumol/liter) suppressed almost completely intercellular but not cellular fluorescence. It is concluded that hepatocytes in culture show a functional polarity permitting the transcellular transport of substances bound for biliary secretion.

Animals↗
PubMed1981

Enzymatic determination of bile acids from liver cells with 3 alpha-hydroxysteroid dehydrogenase--a warning.

3 alpha-Hydroxysteroid dehydrogenase was used to monitor bile acid production by rat hepatocyte suspensions. Several observations suggested that the method lacked specificity and detected some other metabolites besides bile acids. This was due to a malate dehydrogenase activity present in four different commercial enzyme preparations of 3 alpha-hydroxysteroid dehydrogenase. It is concluded that considerable error can be caused by this contaminating malate dehydrogenase activity, especially in the case of low bile acid concentration in the sample.

3-Hydroxysteroid Dehydrogenases↗
PubMed1980

Taurocholate inhibits the glucocorticoid-induced rise of 3-hydroxy-3-methylglutaryl-CoA reductase in primary culture of hepatocytes.

The influence of taurocholate, the major bile acid of the rat, on 3-hydroxy-3-methylglutaryl-CoA reductase [mevalonate: NADP+ oxidoreductase (acylating CoA); EC 1.1.1.34], the regulatory enzyme of cholesterol synthesis, was studied in primary cultures of rat hepatocytes. The basal activity of the enzyme was not altered by adding up to 10 microM taurocholate to the culture medium. On the contrary, 1nM to 10 microM taurocholate caused a dose-dependent inhibition of enzyme activity within 6 h if added simultaneously with 10 microM dexamethasone. Because this glucocorticoid causes a cycloheximide-sensitive rise of 3-hydroxy-3-methylglutaryl-CoA reductase activity in this system the results are taken as evidence that bile salts inhibit the synthesis of the enzyme. The induction of tyrosine transaminase (L-tyrosine:2-oxoglutarate aminotransferase; EC 2.6.1.5) by dexamethasone was not influenced by taurocholate, which demonstrates that the glucocorticoid sensitivity of the cells was not impaired by the bile salt. It is concluded that there is a direct control of hepatic cholesterol synthesis by bile salts.

Animals↗
PubMed1980

Inhibition of cholesterol synthesis in rat liver by physiological doses of taurocholate.

This report deals with the controversial problem whether bile acids exert a direct inhibitory effect on the rate of hepatic cholesterol synthesis. For this purpose rats have been provided with an 'extracorporeal bile duct', an experimental model which makes it possible to initiate a bile fistula two weeks after last surgery. In the animals that recovered completely from operative trauma, a 6-h infusion of 33.4 mumol sodium taurocholate x (100 g body weight)-1 x h-1, prevented the threefold rise of hepatic cholesterol synthesis following bile diversion. The rate of cholesterol synthesis was monitored by incorporation of [14C] acetate in vitro. There was no difference whether the animals were infused from 4--10 h (dark/light transition) or from 16--22 h (light/dark transition) besides the fact that taurocholate caused a more extensive inhibition during the light-dark transition. A parallel kind of response was observed for the activity of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (EC 1.1.1.34), the regulatory enzyme of cholesterol synthesis. A twofold rise of hepatic fatty acid synthesis was observed following bile diversion which was not seen in case of simultaneous bile salt infusion. It is concluded that bile salts exert direct feedback inhibition of hepatic cholesterol synthesis and that opposite results reported by other investigators are probably due to the infusion of too low doses of taurocholate.

Animals↗
PubMed1980

Morphology and metabolism of adult rat hepatocytes in primary culture.

Isolated hepatocytes obtained by collagenase perfusion of adult rat livers were seeded on collagen gels and kept in a chemically defined culture medium (except for the first 6 h of culture where 10% fetal calf serum was added). Cells adopted an epitheloid shape within 4 h and arranged themselves in a trabeculae-like pattern during the first 20 h of culture. In the electron microscope numerous tight junctions and bile capillaries were observed at sites of cell-to-cell contact. From metabolite analyses in the culture medium the following conclusions can be drawn: The cells continued to synthesize urea and ketone bodies for 5 days of culture. The cytosolic and mitochondrial redox states of the nicotinamide adenine nucleotide systsm were as in the liver in vivo and the oxygen supply of hepatocytes was sufficient under the culture conditions. Maximal velocities of ketogenesis from octanoate and of urea formation from ornithine plus ammonium chloride were stable during a 120 h culture period and compared well with rates found in the isolated perfused rat liver.

Animals↗
PubMed1979

Taurocholate uptake by adult rat hepatocytes in primary culture.

Adult rat hepatocytes were cultured on Petri dishes for 25--30 h prior to measuring their ability to transport taurocholate. A rapid uptake of the bile acid (25 muM) was observed: about 20% was accumulated in the cells within 15 min. The taurocholate transport was saturable with an apparent Km of 28 +/- 10 muM and a maximal velocity V of 0.07 +/- 0.02 nmol/(micrograms DNA x min). Uptake was shown to be energy dependent as it was inhibited about 65% by antimycin A (20 micrograms/ml). The monohydroxylated bile acid taurolithocholate and the dihydroxylated taurochenodeoxycholate inhibited taurocholate transport to about 30 and 40% resp. of the control. The transport process was strongly dependent on sodium ions. It is concluded that the characteristics of taurocholate uptake into adult rat hepatocytes are very similar either in freshly prepared cells or in hepatocytes which are cultured on Petri dishes for 25--30 h.

Animals↗
PubMed1978

The extracorporeal bile duct: a new model for determination of bile flow and bile composition in the intact rat.

A new model is described which allows measurement of bile flow and sampling of bile in the intact rat with a physiologically functioning sphincter of Oddi. A number of metabolic parameters have been followed to show that animals with such an "extracorporeal bile duct" (EBD) behave as intact controls. Especially, there was no difference in the increase in body weight or hepatic fatty acid and cholesterol synthesis between EBD animals and intact controls. The amount of bile salts circulating through the biliary tract amounted to 30.5+/-1.5mumol . 100 g body wt-1 . hr-1, when diurnal variations were averaged. Animals adapted to a restricted feeding regimen showed a significant increase of bile flow and of biliary bile salt and cholesterol excretion during feeding (10AM-3 PM); these parameters reached their maximum 3 hours after onset of food intake.

Animals↗
PubMed1958

CHEMICAL AERONOMY.

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Journal Article↗