scholarly journals Oxytocin inactivates and phosphorylates rat hepatocyte glycogen synthase

1989 ◽  
Vol 261 (3) ◽  
pp. 827-830 ◽  
Author(s):  
J Ariño ◽  
F Bosch ◽  
A M Gómez-Foix ◽  
J J Guinovart
Keyword(s):  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Electrophoretic Analysis ◽  
Rat Hepatocyte ◽  
Isolated Rat Hepatocytes ◽  
Phosphorylation State ◽  
Dependent Inactivation ◽  
Cnbr Cleavage ◽  
Dose Dependent ◽  
Glycogen Synthase Activity

Incubation of isolated rat hepatocytes with oxytocin produces a time- and dose-dependent inactivation of glycogen synthase. Such inactivation is associated with an increase in the phosphorylation state of the 88 kDa subunit of the enzyme, as observed after electrophoretic analysis of the 32P-labelled enzyme isolated by immunoprecipitation from cells incubated with [32P]phosphate. CNBr cleavage of the immunoprecipitated glycogen synthase showed that multiple sites were phosphorylated after exposure of the cells to the hormone. The effect of oxytocin on hepatocyte glycogen synthase activity was not observed in the absence of extracellular Ca2+. Inactivation of glycogen synthase by oxytocin was partially abolished in the presence of insulin. These results indicate that the effects of oxytocin on glycogen synthase from rat hepatocytes are similar to those observed for other Ca2+-mediated glycogenolytic hormones, such as vasopressin.

scholarly journals Control of glycogen synthase phosphorylation in isolated rat hepatocytes by epinephrine, vasopressin and glucagon

1984 ◽  
Vol 142 (3) ◽  
pp. 511-520 ◽  
Author(s):  
Carlos CIUDAD ◽  
Marcella CAMICI ◽  
Zafeer AHMAD ◽  
Yuhuan WANG ◽  
Anna A. DePAOLI-ROACH ◽  
...  
Keyword(s):  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

scholarly journals Effect of adenosine and inosine on ureagenesis in hepatocytes

1987 ◽  
Vol 245 (2) ◽  
pp. 371-374 ◽  
Author(s):  
R Guinzberg P ◽  
I Laguna ◽  
A Zentella ◽  
R Guzman ◽  
E Piña
Keyword(s):  
Uric Acid ◽  
Rat Hepatocytes ◽  
Physiological Significance ◽  
Isolated Rat Hepatocytes ◽  
Dose Dependent ◽  
Isolated Rat ◽  
Stimulation Of

Adenosine and inosine produced a dose-dependent stimulation of ureagenesis in isolated rat hepatocytes. Hypoxanthine, xanthine and uric acid were without effect. Half-maximally effective concentrations were 0.08 microM for adenosine and 5 microM for inosine. Activation of ureagenesis by both nucleosides had the following characteristics: (a) it was observed with either glutamine or (NH4)2CO3, provided that glucose was present; (b) it was not detected when glucose was replaced by lactate plus oleate; (c) it was mutually antagonized by glucagon, but not by adrenaline; and (d) it was dependent on Ca2+. We suggest that the action of adenosine and inosine on ureagenesis might be of physiological significance.

Effect of membrane potential and cellular ATP on glutathione efflux from isolated rat hepatocytes

1988 ◽  
Vol 255 (4) ◽  
pp. G403-G408 ◽  
Author(s):  
J. C. Fernandez-Checa ◽  
C. Ren ◽  
T. Y. Aw ◽  
M. Ookhtens ◽  
N. Kaplowitz
Keyword(s):  
Membrane Potential ◽  
High Performance ◽  
Direct Relationship ◽  
Rat Hepatocytes ◽  
Antimycin A ◽  
Total Glutathione ◽  
Rat Hepatocyte ◽  
Isolated Rat Hepatocytes ◽  
Carbonyl Cyanide ◽  
Isolated Rat

total glutathione (GSH) efflux was studied in isolated rat hepatocyte suspensions at repleted GSH content (45-55 nmol/10(6) cells). The increase in concentrations of medium K+ in place of Na+ caused a parallel fall in membrane potential and total GSH efflux. Ouabain (1 mM) and replacement of Na+ with choline caused a gradual fall in membrane potential and GSH efflux. Hyperpolarization of hepatocytes with lipophilic anions, thiocyanate, and nitrate was associated with significantly increased efflux. Total GSH efflux was inhibited by increasing concentrations of fructose, antimycin A, and carbonyl cyanide p-trifluoromethoxyphenylhydrazone, and there was a direct relationship between the rate of efflux and cellular ATP. Changes in total GSH efflux were paralleled by changes in GSH determined by high-performance liquid chromatography. Vanadate markedly inhibited efflux but caused only a modest decrease in cellular ATP. Fructose, antimycin A, and vanadate did not affect membrane potential or cell volume under the conditions at which efflux was inhibited. These results suggest independent requirements for both membrane potential and ATP in the transport of GSH.

scholarly journals Calcium rather than cyclic AMP is an intracellular messenger of parathyroid hormone action on glycogen metabolism in isolated rat hepatocytes

1989 ◽  
Vol 258 (3) ◽  
pp. 889-894 ◽  
Author(s):  
T Mine ◽  
I Kojima ◽  
E Ogata
Keyword(s):  
Parathyroid Hormone ◽  
Cyclic Amp ◽  
Glucose Production ◽  
Rat Hepatocytes ◽  
Free Calcium ◽  
Dependent Manner ◽  
Isolated Rat Hepatocytes ◽  
Glucose Output ◽  
Dose Dependent ◽  
Isolated Rat

The synthetic 1-34 fragment of human parathyroid hormone (1-34hPTH) stimulated glucose production in isolated rat hepatocytes. The effect of 1-34hPTH was dose-dependent and 10(10) M-1-34 hPTH elicited the maximum glucose output, which was approx. 80% of that by glucagon. Although 1-34hPTH induced a small increase in cyclic AMP production at concentrations higher than 10(-9) M, 10(-10) M-1-34hPTH induced the maximum glucose output without significant elevation of cyclic AMP. This is in contrast to the action of forskolin, which increased glucose output to the same extent as 10(-10) M-1-34hPTH by causing a 2-fold elevation of cyclic AMP. In addition to increasing cyclic AMP, 1-34hPTH caused an increase in cytoplasmic free calcium concentration ([Ca2+]c). When the effect of 1-34hPTH on [Ca2+]c was studied in aequorin-loaded cells, low concentrations of 1-34hPTH increased [Ca2+]c: the 1-34hPTH effect on [Ca2+]c was detected at as low as 10(-12) M and increased in a dose-dependent manner. 1-34hPTH increased [Ca2+]c even in the presence of 1 microM extracellular calcium, suggesting that PTH mobilizes calcium from an intracellular pool. In line with these observations, 1-34hPTH increased the production of inositol trisphosphate. These results suggest that: (1) PTH activates both cyclic AMP and calcium messenger systems and (2) PTH stimulates glycogenolysis mainly via the calcium messenger system.

Diet and diabetic state modify glycogen synthase activity and expression in rat hepatocytes

2001 ◽  
Vol 12 (8) ◽  
pp. 458-464 ◽  
Author(s):  
Yael Libal-Weksler ◽  
Olga Gotlibovitz ◽  
Aliza H. Stark ◽  
Zecharia Madar
Keyword(s):  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Diabetic State ◽  
Glycogen Synthase Activity

scholarly journals Metabolism of exogenous S-adenosylmethionine in isolated rat hepatocyte suspensions: methylation of plasma-membrane phospholipids without intracellular uptake

1997 ◽  
Vol 327 (2) ◽  
pp. 383-389 ◽  
Author(s):  
Fran¸oise BONTEMPS ◽  
Georges VAN DEN BERGHE
Keyword(s):  
Plasma Membrane ◽  
Animal Models ◽  
Rat Hepatocytes ◽  
Intracellular Uptake ◽  
Membrane Phospholipids ◽  
Rat Hepatocyte ◽  
Isolated Rat Hepatocytes ◽  
Liver Disorders ◽  
Slight Elevation ◽  
Isolated Rat

Administration of S-adenosylmethionine (AdoMet), the main biological methyl donor, has been shown to exert favourable effects on liver disorders in man and animal models. The mechanism of action of AdoMet has, however, remained elusive, mainly owing to controversies with respect to its capacity to enter intact liver cells. Incubation of isolated rat hepatocytes with 2 or 50 μM [methyl-14C]AdoMet showed that it was utilized predominantly to methylate cellular phospholipids, forming mainly phosphatidylcholine, although less than 0.2% of labelled AdoMet was found inside the cells. The concentration of neither AdoMet nor S-adenosylhomocysteine (AdoHcy), its demethylation product, was significantly elevated inside the cells. A slight elevation of intracellular AdoMet was only recorded on incubation with concentrations of AdoMet above 200 μM. AdoHcy, which does not penetrate cells, inhibited phospholipid methylation from [methyl-14C]AdoMet but not from [methyl-14C]Met. Elevation of intracellular AdoHcy by adenosine dialdehyde, an inhibitor of AdoHcy hydrolase, inhibited phospholipid methylation from [methyl-14C]Met, but virtually not at all from [methyl-14C]AdoMet. Taken together, these data indicate that exogenous AdoMet does not penetrate hepatocytes significantly but is utilized for phospholipid methylation on the outer surface of the plasma membrane.

scholarly journals Stimulatory effect of the intestinal peptide PHI on glycogenolysis and gluconeogenesis in isolated rat hepatocytes

1983 ◽  
Vol 214 (3) ◽  
pp. 999-1002 ◽  
Author(s):  
J E Felíu ◽  
J Marco
Keyword(s):  
Cyclic Amp ◽  
Pyruvate Kinase ◽  
Glycogen Phosphorylase ◽  
Rat Hepatocytes ◽  
Fold Increase ◽  
Isolated Rat Hepatocytes ◽  
Mediated Effects ◽  
Dose Dependent ◽  
Isolated Rat ◽  
Stimulation Of

The newly isolated peptide PHI provoked a dose-dependent stimulation of glycogenolysis and gluconeogenesis in isolated rat hepatocytes; at 1 microM-PHI, both processes were increased 1.6-fold as compared with basal values. These PHI-mediated effects were accompanied by the activation of glycogen phosphorylase and the inactivation of pyruvate kinase. PHI (1 microM) also caused a 2-fold increase in hepatocyte cyclic AMP.

Overexpression or ablation of JNK in skeletal muscle has no effect on glycogen synthase activity

2004 ◽  
Vol 287 (1) ◽  
pp. C200-C208 ◽  
Author(s):  
Nobuharu Fujii ◽  
Marni D. Boppart ◽  
Scott D. Dufresne ◽  
Patricia F. Crowley ◽  
Alison C. Jozsi ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Contraction ◽  
Glycogen Synthase ◽  
Contractile Activity ◽  
S6 Kinase ◽  
Jnk Signaling ◽  
Phosphorylation State ◽  
Mouse Skeletal Muscle ◽  
Major Mechanism ◽  
Glycogen Synthase Activity

c-Jun NH2-terminal kinase (JNK) is highly expressed in skeletal muscle and is robustly activated in response to muscle contraction. Little is known about the biological functions of JNK signaling in terminally differentiated muscle cells, although this protein has been proposed to regulate insulin-stimulated glycogen synthase activity in mouse skeletal muscle. To determine whether JNK signaling regulates contraction-stimulated glycogen synthase activation, we applied an electroporation technique to induce JNK overexpression (O/E) in mouse skeletal muscle. Ten days after electroporation, in situ muscle contraction increased JNK activity 2.6-fold in control muscles and 15-fold in the JNK O/E muscles. Despite the enormous activation of JNK activity in JNK O/E muscles, contraction resulted in similar increases in glycogen synthase activity in control and JNK O/E muscles. Consistent with these findings, basal and contraction-induced glycogen synthase activity was normal in muscles of both JNK1- and JNK2-deficient mice. JNK overexpression in muscle resulted in significant alterations in the basal phosphorylation state of several signaling proteins, such as extracellular signal-regulated kinase 1/2, p90 S6 kinase, glycogen synthase kinase 3, protein kinase B/Akt, and p70 S6 kinase, in the absence of changes in the expression of these proteins. These data suggest that JNK signaling regulates the phosphorylation state of several kinases in skeletal muscle. JNK activation is unlikely to be the major mechanism by which contractile activity increases glycogen synthase activity in skeletal muscle.

Dose-Dependent Cytotoxicity of Chlorinated Hydrocarbons in Isolated Rat Hepatocytes

1990 ◽  
Vol 14 (4) ◽  
pp. 833-841
Author(s):  
LENA DAHLSTRÖM-KJNG ◽  
JOHANNE COUTURE ◽  
CLAUDETTE LAMOUREUX ◽  
THÉRÈSE VAILLANCOURT ◽  
GABRIEL L. PLAA
Keyword(s):  
Chlorinated Hydrocarbons ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Dose Dependent ◽  
Isolated Rat
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