scholarly journals Mannitol 1-phosphate mediates an inhibitory effect of mannitol on the activity and the translocation of glucokinase in isolated rat hepatocytes

Diabetologia ◽  
1998 ◽  
Vol 41 (8) ◽  
pp. 947-954 ◽  
Author(s):  
L. Niculescu ◽  
E. Van Schaftingen
Keyword(s):  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

scholarly journals Inhibition of oxidative metabolism by propionic acid and its reversal by carnitine in isolated rat hepatocytes

1986 ◽  
Vol 236 (1) ◽  
pp. 131-136 ◽  
Author(s):  
E P Brass ◽  
P V Fennessey ◽  
L V Miller
Keyword(s):  
Palmitic Acid ◽  
Propionic Acid ◽  
Oxidative Metabolism ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Acid Oxidation ◽  
Isolated Rat Hepatocytes ◽  
Pyruvate Oxidation ◽  
Metabolic Basis ◽  
Isolated Rat

The present study was designed to study the interaction of propionic acid and carnitine on oxidative metabolism by isolated rat hepatocytes. Propionic acid (10 mM) inhibited hepatocyte oxidation of [1-14C]-pyruvate (10 mM) by 60%. This inhibition was not the result of substrate competition, as butyric acid had minimal effects on pyruvate oxidation. Carnitine had a small inhibitory effect on pyruvate oxidation in the hepatocyte system (210 +/- 19 and 184 +/- 18 nmol of pyruvate/60 min per mg of protein in the absence and presence of 10 mM-carnitine respectively; means +/- S.E.M., n = 10). However, in the presence of propionic acid (10 mM), carnitine (10 mM) increased the rate of pyruvate oxidation by 19%. Under conditions where carnitine partially reversed the inhibitory effect of propionic acid on pyruvate oxidation, formation of propionylcarnitine was documented by using fast-atom-bombardment mass spectroscopy. Propionic acid also inhibited oxidation of [1-14C]palmitic acid (0.8 mM) by hepatocytes isolated from fed rats. The degree of inhibition caused by propionic acid was decreased in the presence of 10 mM-carnitine (41% inhibition in the absence of carnitine, 22% inhibition in the presence of carnitine). Propionic acid did not inhibit [1-14C]palmitic acid oxidation by hepatocytes isolated from 48 h-starved rats. These results demonstrate that propionic acid interferes with oxidative metabolism in intact hepatocytes. Carnitine partially reverses the inhibition of pyruvate and palmitic acid oxidation by propionic acid, and this reversal is associated with increased propionylcarnitine formation. The present study provides a metabolic basis for the efficacy of carnitine in patients with abnormal organic acid accumulation, and the observation that such patients appear to have increased carnitine requirements (‘carnitine insufficiency’).

Inhibition of GSH efflux from rat liver by methionine: effects of GSH synthesis in cells and perfused organ

1990 ◽  
Vol 258 (6) ◽  
pp. G967-G973 ◽  
Author(s):  
J. C. Fernandez-Checa ◽  
T. Maddatu ◽  
M. Ookhtens ◽  
N. Kaplowitz
Keyword(s):  
Rat Liver ◽  
Reduced Glutathione ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Perfused Liver ◽  
Isolated Rat Hepatocytes ◽  
Dependent Inhibition ◽  
Krebs Henseleit Buffer ◽  
Isolated Rat ◽  
In Cells

The inhibition of efflux of intracellular reduced glutathione (GSH) by methionine was determined in isolated rat hepatocytes suspended either in Krebs-Henseleit buffer or in modified Fisher's medium. Methionine (1 mM) added to Krebs-Henseleit suspensions of isolated rat hepatocytes inhibited GSH efflux, with greater retention of GSH in the cells compared with control. Results were similar with methionine and 0.3 mM propargylglycine cystathionase inhibitor), suggesting no net synthesis of GSH from methionine. In Fisher's medium, the inhibitory effect of methionine on GSH efflux was masked due to increasing cellular GSH; however, the inhibitory effect of methionine was unmasked by propargylglycine, which prevented the utilization of methionine for GSH synthesis. The addition of serine (0.1 mM) to methionine in Krebs-Henseleit buffer raised cellular GSH, overcoming the inhibition of GSH efflux. In the perfused liver, infusion of 1 and 5 mM methionine initially inhibited GSH efflux, but the inhibition was reversed with continued methionine infusion. After removal of methionine, GSH efflux increased immediately. The reversal and rebound were blocked by propargylglycine, revealing concentration-dependent inhibition of sinusoidal GSH efflux by methionine. Thus, when methionine is utilized to promote GSH synthesis, its inhibitory effect on GSH efflux tends to be overcome.

scholarly journals Effects of protein-degradation inhibitors on the inactivation of tyrosine aminotransferase, tryptophan oxygenase and benzopyrene hydroxylase in isolated rat hepatocytes

1982 ◽  
Vol 202 (1) ◽  
pp. 191-196 ◽  
Author(s):  
B Grinde ◽  
R Jahnsen
Keyword(s):  
Proteinase Inhibitors ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Tyrosine Aminotransferase ◽  
Weak Base ◽  
Isolated Rat Hepatocytes ◽  
Tryptophan Oxygenase ◽  
The Third ◽  
Lysosomal Proteinase ◽  
Isolated Rat

The following three potent inhibitors of hepatocytic proteolysis were investigated to see if they would inhibit the intracellular inactivation of enzymes: chymostatin and leupeptin (proteinase inhibitors) and methylamine (a lysosomotropic weak base). Chymostatin inhibited the inactivation of two of the three enzymes tested: tyrosine aminotransferase (EC 2.6.1.5) and tryptophan oxygenase (tryptophan 2,3-dioxygenase, EC 1.13.11.11). Leupeptin had no effect on any of the enzymes, whereas methylamine had only a weak inhibitory effect on tyrosine aminotransferase inactivation. Apparently proteolytic cleavage (probably by a non-lysosomal proteinase, since only chymostatin is effective) is involved in the inactivation of tyrosine aminotransferase and tryptophan oxygenase. The third enzyme, benzopyrene hydroxylase (flavoprotein-linked mono-oxygenase, EC 1.14.14.1), is probably inactivated by a non-proteolytic mechanism.

scholarly journals Inhibition of phosphatidylethanolamine synthesis by glucagon in isolated rat hepatocytes

1989 ◽  
Vol 257 (3) ◽  
pp. 645-650 ◽  
Author(s):  
L B M Tijburg ◽  
M Houweling ◽  
M J H Geelen ◽  
L M G Van Golde
Keyword(s):  
Cyclic Amp ◽  
De Novo ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Isolated Rat Hepatocytes ◽  
Ethanolamine Phosphate ◽  
Isolated Rat

Exposure of isolated rat hepatocytes to glucagon or chlorophenylthio cyclic AMP led to an inhibition of the incorporation of [1,2-14C]ethanolamine into phosphatidylethanolamine. Pulse-chase experiments and measurement of the activities of the enzymes involved in the CDP-ethanolamine pathway provided evidence that the inhibitory effect of glucagon on the synthesis de novo of phosphatidylethanolamine was not caused by a diminished conversion of ethanolamine phosphate into CDP-ethanolamine. The observations suggested that the glucagon-induced inhibition of the biosynthesis of phosphatidylethanolamine is probably due to a decreased supply of diacylglycerols, resulting in a decreased formation of phosphatidylethanolamine from CDP-ethanolamine and diacylglycerols.

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