scholarly journals Stimulation of glycogenolysis in isolated hepatocytes by adenosine and one of its analogues is inhibited by caffeine

1987 ◽  
Vol 247 (3) ◽  
pp. 779-783 ◽  
Author(s):  
J C Stanley ◽  
J Markovic ◽  
A M Gutknecht ◽  
F J Lozeman
Keyword(s):  
Adenosine Receptors ◽  
Glycogen Phosphorylase ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Effective Concentration ◽  
Physiological Concentration ◽  
Endogenous Adenosine ◽  
Phenylisopropyl Adenosine ◽  
Stimulation Of ◽  
A2 Adenosine Receptors

The adenosine analogues 5′-(N-ethyl)carboxamidoadenosine (NECA) and N6-(phenylisopropyl)adenosine (PIA) activate glycogen phosphorylase 5-fold and 4.2-fold respectively in rat hepatocytes incubated in the absence of endogenous adenosine. Half-maximally effective concentrations are 0.5 microM for NECA and 20 microM for PIA, demonstrating the presence of A2-adenosine receptors. Exogenous adenosine activates phosphorylase 4.6-fold, but high rates of adenosine disappearance from the medium render estimates of its half-maximally effective concentration unreliable. These effects of NECA and adenosine are inhibited by 0.1 mM-caffeine. Activation of phosphorylase by a physiological concentration of adenosine (3.3 microM) was 50% inhibited by a physiological concentration of caffeine (35 microM).

scholarly journals Effect of calcium ions on ethanol oxidation and drug glucuronidation in isolated hepatocytes

1979 ◽  
Vol 184 (3) ◽  
pp. 709-711 ◽  
Author(s):  
B Andersson ◽  
D P Jones ◽  
S Orrenius
Keyword(s):  
Drug Metabolism ◽  
Calcium Ions ◽  
Ethanol Oxidation ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Physiological Concentration ◽  
Isolated Rat Hepatocytes ◽  
Similar Dependence ◽  
Isolated Rat ◽  
Stimulation Of

The effect of extracellular Ca2+ concentration on ethanol oxidation and drug metabolism was studied in isolated rat hepatocytes. Both ethanol oxidation and drug glucuronidation showed similar dependence upon Ca2+, which was a stimulation of activity as Ca2+ was increased to physiological concentration, and inhibition at higher concentration.

scholarly journals Characterization of the liver P2-purinoceptor involved in the activation of glycogen phosphorylase

1986 ◽  
Vol 240 (2) ◽  
pp. 367-371 ◽  
Author(s):  
S Keppens ◽  
H De Wulf
Keyword(s):  
Binding Sites ◽  
Glycogen Phosphorylase ◽  
Plasma Membranes ◽  
Specific Binding ◽  
Rank Order ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
P2 Purinoceptors

Evidence has been presented for the existence in rat liver of P2-purinoceptors which are involved in the control of glycogenolysis. Isolated rat hepatocytes and purified liver plasma membranes have been used to study the binding of the ATP analogue adenosine 5′-[alpha- [35S]thio]triphosphate (ATP alpha [35S]) to these postulated P2-purinoceptors. The nucleotide analogue behaves as a full agonist for the activation of glycogen phosphorylase in isolated hepatocytes, 0.3 microM being required for half-maximal activation. Specific binding of ATP alpha [35S] to hepatocytes and plasma membranes occurs within 1 min and is essentially reversible. The analysis of the dose-dependency at equilibrium indicates the presence of binding sites with Kd of 0.23 microM with hepatocytes and Kd of 0.11 microM with plasma membranes. The relative affinities of 10 nucleotide analogues were deduced from competition experiments for ATP alpha [35S] binding to hepatocytes, and these correlated highly with their biological activity (activation of glycogen phosphorylase in hepatocytes). For all the agonists, binding occurs in the same concentration range as the biological effect. These data clearly suggest that the detected binding sites correspond to the physiological P2-purinoceptors involved in the regulation of liver glycogenolysis. The rank order of potency of some ATP analogues suggests that liver possesses the P2Y-subclass of P2-purinoceptors.

scholarly journals Phosphatidylinositol metabolism in rat hepatocytes stimulated by vasopressin

1981 ◽  
Vol 194 (1) ◽  
pp. 155-165 ◽  
Author(s):  
C J Kirk ◽  
R H Michell ◽  
D A Hems
Keyword(s):  
Glycogen Phosphorylase ◽  
Equilibrium Distribution ◽  
Rat Hepatocytes ◽  
Subcellular Fractionation ◽  
Isolated Rat Hepatocytes ◽  
Phosphatidylinositol Metabolism ◽  
Maximal Activation ◽  
Vasopressin Receptors ◽  
Stimulation Of

In isolated rat hepatocytes, vasopressin evoked a large increase in the incorporation of [32P]Pi into phosphatidylinositol, accompanied by smaller increases in the incorporation of [1-14C]oleate and [U-14C]glycerol. Incorporation of these precursors into the other major phospholipids was unchanged during vasopressin treatment. Vasopressin also promoted phosphatidylinositol breakdown in hepatocytes. Half-maximum effects on phosphatidylinositol breakdown and on phosphatidylinositol labelling occurred at about 5 nM-vasopressin, a concentration at which approximately half of the hepatic vasopressin receptors are occupied but which is much greater than is needed to produce half-maximal activation of glycogen phosphorylase. Insulin did not change the incorporation of [32P]Pi into the phospholipids of hepatocytes and it had no effect on the response to vasopressin. Although the incorporation of [32P]Pi into hepatocyte lipids was decreased when cells were incubated in a Ca2+-free medium, vasopressin still provoked a substantial stimulation of phosphatidylinositol labelling under these conditions. Studies with the antagonist [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid),8-arginine]vasopressin indicated that the hepatic vasopressin receptors that control phosphatidylinositol metabolism are similar to those that mediate the vasopressor response in vivo. When prelabelled hepatocytes were stimulated for 5 min and then subjected to subcellular fractionation. The decrease in [3H]phosphatidylinositol content in each cell fraction with approximately in proportion to its original phosphatidylinositol content. This may be a consequence of phosphatidylinositol breakdown at a single site, followed by rapid phosphatidylinositol exchange between membranes leading to re-establishment of an equilibrium distribution.

scholarly journals Prostaglandins E2 and F2α increase fructose 2,6-bisphosphate levels in isolated hepatocytes

1991 ◽  
Vol 274 (1) ◽  
pp. 309-312 ◽  
Author(s):  
A M Gómez-Foix ◽  
J E Rodríguez-Gil ◽  
J J Guinovart ◽  
F Bosch
Keyword(s):  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Glycolytic Flux ◽  
Dependent Manner ◽  
Hepatic Glucose Metabolism ◽  
Prostaglandin F2 Alpha ◽  
Hepatic Glucose ◽  
Dose Dependent ◽  
Prostaglandins E2 And F2α ◽  
Stimulation Of

In hepatocytes isolated from fed rats, prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) increased, in a time- and dose-dependent manner, fructose 2,6-bisphosphate [Fru(2,6)P2] levels and stimulated the glycolytic flux. The rise in Fru(2,6)P2 was related to an increase in glucose 6-phosphate levels which resulted from the stimulation of glycogenolysis. In cells obtained from 24 h-starved rats, no effects of either PGE2 or PGF2 alpha could be observed. In addition, when the stimulation of glycogenolysis was abolished by incubation of fed-rat hepatocytes in a Ca2(+)-depleted medium, Fru(2,6)P2 levels did not increase. Furthermore, no effects of PGs on 6-phosphofructo-2-kinase activity could be observed. These results indicate that PGE2 and PGF2 alpha show similar actions to Ca2(+)-dependent hormones on hepatic glucose metabolism.

Characterization of glucagon and catecholamine effects on isolated sheep hepatocytes

1988 ◽  
Vol 255 (4) ◽  
pp. R539-R546
Author(s):  
C. Morand ◽  
C. Yacoub ◽  
C. Remesy ◽  
C. Demigne
Keyword(s):  
Rat Liver ◽  
Glycogen Phosphorylase ◽  
Plasma Membranes ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Cyclic Monophosphate ◽  
Sheep Liver ◽  
Beta Agonists ◽  
Rat Liver Cells

The purpose of this study was to characterize the glycogenolytic response to catecholamines and glucagon in isolated sheep hepatocytes. In this species, epinephrine appeared to exert its action on hepatic glycogenolysis by altering the cytosolic concentrations of both adenosine 3',5'-cyclic monophosphate (cAMP) and Ca2+. In contrast to results obtained in rat hepatocytes, glucagon failed to induce a rise in free cytosolic Ca2+ in sheep liver. Experiments on isolated hepatocytes or on liver plasma membranes showed that in sheep, glucagon was more efficient than epinephrine in promoting the production of cAMP. In the presence of glucagon or epinephrine, the activation of the glycogen phosphorylase a always appeared greater in sheep than in rat liver cells, whereas the variations in cellular cAMP were quite limited in sheep. The alpha 1- and beta-agonists (phenylephrine and isoproterenol) were alone as efficient as epinephrine in promoting phosphorylase a activation in sheep hepatocytes. All these results indicate the existence in sheep liver of a glycogen phosphorylase highly responsive to hormones.

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.

scholarly journals Insulin stimulates synthesis of soluble proteins in isolated rat hepatocytes

1980 ◽  
Vol 190 (3) ◽  
pp. 615-619 ◽  
Author(s):  
R L Clark ◽  
R J Hansen
Keyword(s):  
Protein Synthesis ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Cellular Protein ◽  
Soluble Proteins ◽  
Leucine Incorporation ◽  
Isolated Rat Hepatocytes ◽  
Hepatic Protein Synthesis ◽  
Isolated Rat ◽  
Stimulation Of

The incorporation of [3H]leucine into soluble cellular protein was measured in isolated hepatocytes at extracellular leucine concentrations ranging from 0.15 to 20.0 mM. Insulin caused a 12—15% stimulation of [3H]leucine incorporation in the presence of high extracellular leucine concentrations. It is concluded that insulin causes a small but significant increase in the rate of hepatic protein synthesis.

scholarly journals Effects of vasopressin and La3+ on plasma-membrane Ca2+ inflow and Ca2+ disposition in isolated hepatocytes. Evidence that vasopressin inhibits Ca2+ disposition

1986 ◽  
Vol 238 (3) ◽  
pp. 793-800 ◽  
Author(s):  
B P Hughes ◽  
S E Milton ◽  
G J Barritt
Keyword(s):  
Plasma Membrane ◽  
Glycogen Phosphorylase ◽  
Subcellular Fractionation ◽  
Isolated Hepatocytes ◽  
Ionophore A23187 ◽  
Phosphorylase Activity ◽  
45Ca Uptake ◽  
Maximal Stimulation ◽  
Glycogen Phosphorylase Activity ◽  
Stimulation Of

Vasopressin caused a 40% inhibition of 45Ca uptake after the addition of 0.1 mM-45Ca2+ to Ca2+-deprived hepatocytes. At 1.3 mM-45Ca2+, vasopressin and ionophore A23187 each caused a 10% inhibition of 45Ca2+ uptake, whereas La3+ increased the rate of 45Ca2+ uptake by Ca2+-deprived cells. Under steady-state conditions at 1.3 mM extracellular Ca2+ (Ca2+o), vasopressin and La3+ each increased the rate of 45Ca2+ exchange. The concentrations of vasopressin that gave half-maximal stimulation of 45Ca2+ exchange and glycogen phosphorylase activity were similar. At 0.1 mM-Ca2+o, La3+ increased, but vasopressin did not alter, the rate of 45Ca2+ exchange. The results of experiments performed with EGTA or A23187 or by subcellular fractionation indicate that the Ca2+ taken up by hepatocytes in the presence of La3+ is located within the cell. The addition of 1.3 mM-Ca2+o to Ca2+-deprived cells caused increases of approx. 50% in the concentration of free Ca2+ in the cytoplasm [(Ca2+]i) and in glycogen phosphorylase activity. Much larger increases in these parameters were observed in the presence of vasopressin or ionophore A23187. In contrast with vasopressin, La3+ did not cause a detectable increase in glycogen phosphorylase activity or in [Ca2+]i. It is concluded that an increase in plasma membrane Ca2+ inflow does not by itself increase [Ca2+]i, and hence that the ability of vasopressin to maintain increased [Ca2+]i over a period of time is dependent on inhibition of the intracellular removal of Ca2+.

scholarly journals Molybdate and tungstate act like vanadate on glucose metabolism in isolated hepatocytes

1992 ◽  
Vol 282 (3) ◽  
pp. 659-663 ◽  
Author(s):  
C Fillat ◽  
J E Rodríguez-Gil ◽  
J J Guinovart
Keyword(s):  
Glucose Metabolism ◽  
Glycogen Phosphorylase ◽  
Kinase Activity ◽  
Glycogen Synthase ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
The Other ◽  
Co2 Production ◽  
Glycolytic Flux ◽  
Dependent Mechanism

In rat hepatocytes, molybdate and tungstate inactivate glycogen synthase by a mechanism independent of Ca2+ and activate glycogen phosphorylase by a Ca(2+)-dependent mechanism. On the other hand, both molybdate and tungstate increase fructose 2,6-bisphosphate levels and counteract the decrease in this metabolite induced by glucagon. These effectors do not directly modify 6-phosphofructo-2-kinase activity, even though they partially counteract the inactivation of this enzyme induced by glucagon. These effects are related to an increase on the glycolytic flux, as indicated by the increase in L-lactate and CO2 production and the decrease in glucose 6-phosphate levels in the presence of glucose. All these effects are similar to those previously reported for vanadate, although molybdate and tungstate are less effective than vanadate. These results could indicate that molybdate, tungstate and vanadate act on glucose metabolism in isolated hepatocytes by a similar mechanism of action.

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