scholarly journals Mechanism of activation of glycogen phosphorylase by fructose in the liver. Stimulation of phosphorylase kinase related to the consumption of adenosine triphosphate

1979 ◽  
Vol 178 (1) ◽  
pp. 119-126 ◽  
Author(s):  
G Van de Werve ◽  
H G Hers
Keyword(s):  
High Speed ◽  
Glycogen Phosphorylase ◽  
Isolated Hepatocytes ◽  
Phosphorylase Kinase ◽  
Free Medium ◽  
Histone Kinase ◽  
Dose Dependent ◽  
High Speed Supernatant ◽  
Stimulation Of

1. A dose-dependent activation of phosphorylase and consumption of ATP was observed in isolated hepatocytes incubated in the presence of fructose; histone kinase and phosphorylase kinase activities were unchanged at doses of this sugar that were fully effective on phosphorylase. The activation of phosphorylase by fructose was also observed in cells incubated in a Ca2+-free medium as well as in the livers of rats in vivo. 2. In a liver high-speed supernatant, fructose, tagatose and sorbose stimulated the activity of phosphorylase kinase; this effect was dependent on the presence of K+ ions, which are required for the activity of fructokinase; it was accompanied by the transformation of ATP into ADP. In the presence of hexokinase, glucose also stimulated phosphorylase kinase, both in an Na+ or a K+ medium. 3. The activities of partially purified muscle or liver phosphorylase kinase were unchanged in the presence of fructose. 4. Some properties of liver phosphorylase kinase are described, including a high molecular weight and an inhibition at ATP/Mg ratios above 0.5, as well as an effect of ATP concentration on the hysteretic behaviour of this enzyme. 5. The effect of fructose on the activation of phosphorylase is discussed in relation to the comsumption of ATP.

scholarly journals The ability of adenosine to decrease the concentration of fructose 2,6-bisphosphate in isolated hepatocytes. A cyclic AMP-mediated effect

1984 ◽  
Vol 218 (1) ◽  
pp. 157-163 ◽  
Author(s):  
R Bartrons ◽  
E Van Schaftingen ◽  
H G Hers
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Pyruvate Kinase ◽  
High Speed ◽  
Opposite Effect ◽  
Marked Decrease ◽  
Isolated Hepatocytes ◽  
Adenosine Transport ◽  
High Speed Supernatant ◽  
Stimulation Of

The presence of adenosine (25-250 microM) or of 2-chloroadenosine (2.5-100 microM) in the incubation medium caused a marked decrease in the concentration of fructose 2,6-bisphosphate in isolated hepatocytes. This effect was accompanied by an increase in the concentration of cyclic AMP, an activation of phosphorylase and of fructose 2,6-bisphosphatase, and an inactivation of pyruvate kinase and of 6-phosphofructo-2-kinase. As a rule, the changes in the fructose 2,6-bisphosphate-modifying system were slower but more persistent than those in the activities of phosphorylase and pyruvate kinase. The effect of the nucleoside to decrease the concentration of fructose 2,6-bisphosphate was not affected by an inhibitor of adenosine transport and could not be obtained in a liver high-speed supernatant. These data indicate that the effect of adenosine to decrease the concentration of fructose 2,6-bisphosphate is mediated by the stimulation of adenylate cyclase, secondary to the binding of adenosine to membranous receptors. Like glucagon, 2-chloroadenosine stimulated gluconeogenesis in isolated hepatocytes, whereas adenosine had an opposite effect.

scholarly journals Hormonal and ionic control of the glycogenolytic cascade in rat liver

1977 ◽  
Vol 162 (1) ◽  
pp. 135-142 ◽  
Author(s):  
G van de Werve ◽  
L Hue ◽  
H G Hers
Keyword(s):  
Rat Liver ◽  
Incubation Medium ◽  
Liver Extract ◽  
Isolated Hepatocytes ◽  
Phosphorylase Kinase ◽  
High Concentration ◽  
Unanesthetized Animals ◽  
Histone Kinase ◽  
Dose Dependent

1. A parallel dose-dependent activation of histone kinase, phosphorylase kinase and phosphorylase was observed in isolated hepatocytes incubated in the presence of glucagon; the effect of suboptimal concentrations of glucagon was antagonized by insulin. 2. An activation of phosphorylase which was not accompanied by a stable change in the activity of phosphorylase kinase was observed in hepatocytes incubated with phenylephrine, isoproterenol or vasopressin as well as on decapitation of unanesthetized animals. A dissociation of the two enzymic activities was also observed in hepatocytes incubated in the presence of a high concentration of glucose, in which phosphorylase was strongly inactivated with no change in the activity of phosphorylase kinase. 3. The activation of phosphorylase by phenylephrine in isolated hepatocytes was counteracted by insulin, greatly decreased by the absence of Ca2+ from the incubation medium, and completely suppressed by the replacement of Na+ by K+. 4. In a liver extract, phosphorylase kinase could also be activated by trypsin. Control, glucagon-activated or trypsin-activated phosphorylase kinase was inhibited by about 70% by EGTA and the activity was restored by the addition of Ca2+. 5. The mechanisms that control the activity of phosphorylase kinase and of phosphorylase are discussed.

scholarly journals Stimulation of collagen galactosyltransferase and glucosyltransferase activities by lysophosphatidylcholine

1976 ◽  
Vol 160 (1) ◽  
pp. 29-35 ◽  
Author(s):  
H Anttinen
Keyword(s):  
Chick Embryo ◽  
High Speed ◽  
Membrane Structures ◽  
Embryo Extract ◽  
Chick Embryo Extract ◽  
Triton X ◽  
Regulatory Significance ◽  
Stimulation Of

Lysophosphatidylcholine stimulated the activities of collagen galactosyl- and glucosyl-transferases in chick-embryo extract and its particulate fractions in vitro, whereas essentially no stimulation was noted in the high-speed supernatant, where the enzymes are soluble and membrane-free. The stimulatory effect of lysophosphatidylcholine was masked by 0.1% Triton X-100. In kinetic experiments lysophosphatidylcholine raised the maximum velocities with respect to the substrates and co-substrates, whereas no changes were observed in the apparant Km values. Phospholipase A preincubation of the chick-embryo extract resulted in stimulation of both transferase activities, probably gy generating lysophosphatides from endogenous phospholipids. No stimulation by lysophosphatidylcholine was found when tested with 500-fold-purified glycosyltransferase. The results suggest that collagen glycosyltransferases must be associated with the membrane structures of the cell in order to be stimulated by lysophosphatidylcholine. Lysophosphatidylcholine could have some regulatory significance in vivo, since its concentration in the cell is comparable with that which produced marked stimulation in vitro.

Dose-dependent shifts in the sulfation and glucuronidation of phenolic compounds in the rat in vivo and in isolated hepatocytes

1981 ◽  
Vol 30 (18) ◽  
pp. 2569-2575 ◽  
Author(s):  
Henk Koster ◽  
Ina Halsema ◽  
Egbert Scholtens ◽  
Marjan Knippers ◽  
Gerard J. Mulder
Keyword(s):  
Phenolic Compounds ◽  
Isolated Hepatocytes ◽  
Dose Dependent

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.

Changes in skeletal muscle glycogenolysis after prolonged cold exposure and repeated injections with isoproterenol

1979 ◽  
Vol 57 (9) ◽  
pp. 938-943 ◽  
Author(s):  
M. C. Thibault ◽  
C. Côté ◽  
J. Vallières
Keyword(s):  
Adenylate Cyclase ◽  
Cold Stress ◽  
Tibialis Anterior ◽  
Skeletal Muscles ◽  
Glycogen Phosphorylase ◽  
Phosphorylase Kinase ◽  
Adenylate Cyclase System ◽  
Great Capacity ◽  
Contracting Muscle

Wistar rats were either given daily injections of isoproterenol (ISO) (15 μg/100 g per day) or exposed to 6 °C for 4 or 12 weeks (cold acclimated (CA)). After a 4-week exposure to cold and to ISO, acute cold stress (4 h at –18 °C) produced a 48% depletion of glycogen in the tibialis anterior of control rats while it did not significantly affect the levels in ISO-treated and CA animals. ISO treatment enhanced the in vivo response of phosphorylase kinase and glycogen phosphorylase to epinephrine (EPI) in the tibialis anterior, a fast contracting muscle. In the soleus, a slow contracting muscle known to be more sensitive to catecholamines, chronic treatment with ISO also resulted in increased basal and EPI-stimulated adenylate cyclase activity. No evidence could be found for an alteration of the glycogenolytic pathway (adenylate cyclase system, phosphorylase kinase, and glycogen phosphorylase) in fast contracting skeletal muscles of CA rats. It is concluded that ISO-treated and CA rats, which have a great capacity for nonshivering thermogenesis, do not rely on their muscle carbohydrate reserves during cold stress. It might be suggested that plasma levels of catecholamines higher than those produced by exposure to 6 °C are required to alter glycogenolytic mechanisms in fast contracting rat skeletal muscles.

scholarly journals An in Vitro Model of Post-Exercise Hepatic Gluconeogenesis in the Gulf Toadfish Opsanus Beta

1989 ◽  
Vol 147 (1) ◽  
pp. 393-406 ◽  
Author(s):  
PATRICK J. WALSH
Keyword(s):  
Isolated Hepatocytes ◽  
Blood Parameters ◽  
Strenuous Exercise ◽  
Hepatic Gluconeogenesis ◽  
Post Exercise ◽  
Opsanus Beta ◽  
Stimulation Of ◽  
Gulf Toadfish

During strenuous exercise, fish develop substantial proton and lactate loads. Although acidosis is usually rapidly corrected during recovery (1–2 h), lactate levels often remain elevated for up to 8–12 h. The quantitative role of the liver in clearance of the lactate load during recovery from exercise in fish has received little direct examination. The purposes of this study were (1) to attempt to quantify hepatic contribution to lactate clearance, and (2) to identify factors that regulate hepatic gluconeogenesis during recovery from exercise in fish. Both in vivo and in vitro (isolated hepatocytes) approaches were used. Important blood parameters (pHe, Ccoco2, [lactate], [glucose], [epinephrine] and [norepinephrine]) were measured in the gulf toadfish (Opsanus beta Goode and Bean) during recovery from strenuous exercise, and they conformed to the general patterns for sluggish benthic species noted in earlier studies. When toadfish hepatocytes wereexposed to simulated post-exercise conditions in vitro, gluconeogenesis from lactate was stimulated by over 2.5-fold in ‘0–1 h-’ and ‘l-2h-post-exercise periods’. Variation of the extracellular parameters in controlled combinations indicated that exercise-induced changes in [glucose], [epinephrine], [norepinephrine], Pcoco2 and [HCO3−] had no significant effects on rates of gluconeogenesis.The observed stimulation of gluconeogenesis could be induced independently byeither decreased pH (which lowered Km for lactate) or increased [lactate] (bysimple hyperbolic kinetic effects), but the effects were not additive. Despite thispotentially adaptive stimulation of gluconeogenesis, I estimate, based on observedin vitro rates and in vivo estimates of lactate load, that hepatic gluconeogenesisaccounts for less than 2% of the lactate load clearance in toadfish.

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