scholarly journals Sugar uptake by fluid-phase pinocytosis and diffusion in isolated rat hepatocytes

1987 ◽  
Vol 243 (3) ◽  
pp. 655-660 ◽  
Author(s):  
P B Gordon ◽  
H Høyvik ◽  
P O Seglen
Keyword(s):  
Plasma Membrane ◽  
Fluid Phase ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Free Sugar ◽  
Sugar Uptake ◽  
Isolated Rat Hepatocytes ◽  
Fluid Phase Endocytosis ◽  
And Diffusion ◽  
Isolated Rat

Measurements of sugar pinocytosis (fluid-phase endocytosis of radiolabelled sucrose, lactose and raffinose) in freshly isolated rat hepatocytes are disturbed by sugar diffusing into the cells through plasma-membrane blebs. Non-pinocytic entry may be even more pronounced at 0 degrees C, and is a major contributor to ‘background’ radioactivity. By electrodisruption of the plasma membrane, a distinction can be made between pinocytotically sequestered sugar and free sugar that has entered the cytosol by diffusion. Pinocytosis proceeds at a rate of 2%/h (relative to the intracellular fluid volume), whereas the rate of sucrose entry by diffusion is more than twice as high. Three pinocytotic compartments are distinguishable in isolated hepatocytes: (1) a rapidly recycling compartment, which is completely destroyed by electrodisruption, and which may represent pinocytic channels continuous with the plasma membrane; (2) a non-recycling (or very slowly recycling) electrodisruption-resistant compartment, which allows accumulation of the lysosomally hydrolysable sugar lactose, and which therefore must represent non-lysosomal vacuoles (endosomes?); (3) a lysosomal compartment (non-recycling, electrodisruption-resistant), which accumulates raffinose and sucrose, but which hydrolyses lactose. The last two compartments can be partially resolved in metrizamide/sucrose density gradients by the use of different sugar probes.

Time course of ethanol-induced impairment in fluid-phase endocytosis in isolated rat hepatocytes

Hepatology ◽  
1993 ◽  
Vol 17 (4) ◽  
pp. 661-667 ◽  
Author(s):  
Kenneth B. Camacho ◽  
Carol A. Casey ◽  
Robert L. Wiegert ◽  
Michael F. Sorrell ◽  
Dean J. Tuma
Keyword(s):  
Time Course ◽  
Fluid Phase ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Fluid Phase Endocytosis ◽  
Isolated Rat

scholarly journals Novel evidence for an ecto-phospholipid methyltransferase in isolated rat hepatocytes

1998 ◽  
Vol 330 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Françoise BONTEMPS ◽  
Georges VAN DEN BERGHE
Keyword(s):  
Plasma Membrane ◽  
Phospholipase C ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Methyl Group ◽  
Methyl Donor ◽  
External Face ◽  
Subsequent Addition ◽  
Isolated Rat

Phospholipids of isolated rat hepatocytes were labelled by preincubation with either 2 μM [methyl-14C]S-adenosylmethionine (AdoMet) or 2 μM [methyl-14C]methionine. Subsequent addition of phospholipase C to the suspension removed 95% of the radioactivity from phospholipids methylated by [methyl-14C]AdoMet within a few minutes, but was without effect on phospholipids methylated by [methyl-14C]methionine radioactivity from the latter could, nevertheless, be removed by phospholipase C after permeabilization of the cells with digitonin. The results clearly show that the methyl group of exogenous AdoMet, contrary to that of methionine, is transferred on to phospholipids located on the external face of the plasma membrane. Accordingly, pretreatment of isolated hepatocytes with trypsin prevented the methylation of phospholipids from exogenous AdoMet by 60-80%, whereas it was almost without effect when exogenous methionine was the methyl donor. Our data corroborate previous work [Bontemps and Van den Berghe (1997) Biochem. J. 327, 383-389], which indicated that AdoMet methylates hepatocyte phospholipids without penetrating the cells.

Inhibition of gluconeogenesis by extracellular ATP in isolated rat hepatocytes

1991 ◽  
Vol 261 (6) ◽  
pp. R1522-R1526 ◽  
Author(s):  
M. Asensi ◽  
A. Lopez-Rodas ◽  
J. Sastre ◽  
J. Vina ◽  
J. M. Estrela
Keyword(s):  
Plasma Membrane ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Extracellular Atp ◽  
Structural Analogue ◽  
Isolated Rat Hepatocytes ◽  
Lactate And Pyruvate ◽  
Alpha Beta ◽  
High Concentrations ◽  
Isolated Rat

The aim of this study was to determine the effect of externally added ATP on gluconeogenesis by isolated hepatocytes from starved rats. High concentrations of extracellular ATP inhibited gluconeogenesis from lactate and pyruvate but not from glycerol or fructose. This inhibition was associated with an increase in intracellular adenosine contents. ADP, AMP, or adenosine but not guanosine 5'triphosphate, inosine 5' triphosphate, or adenine also inhibited gluconeogenesis. alpha, beta-Methylene-ATP, a nonmetabolizable structural analogue of ATP, did not affect the rate of gluconeogenesis. Intracellular ATP levels were increased by externally added ATP or adenosine, but ATP-to-ADP ratios in the cytosolic and mitochondrial compartments were diminished. Malate and phosphoenolpyruvate contents were decreased by extracellular ATP or adenosine. Our results show that inhibition of gluconeogenesis by high levels of extracellular ATP may be mediated by adenosine derived from ATP catabolism at the plasma membrane.

Plasma membrane fluidity in isolated rat hepatocytes: A comparative study using DPH and TMA-DPH as fluorescent probes

1989 ◽  
Vol 4 (3) ◽  
pp. 221-227 ◽  
Author(s):  
ANTONIO BENEDETTI ◽  
GIANNA FERRETTI ◽  
GIOVANNA CURATOLA ◽  
EUGENIO BRUNELLI ◽  
ANNE MARIE JÉZÉQUEL ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Comparative Study ◽  
Membrane Fluidity ◽  
Fluorescent Probes ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Plasma Membrane Fluidity ◽  
Isolated Rat

Agonist-induced internalisation of the angiotensin II-binding sites from plasma membranes of isolated rat hepatocytes

1997 ◽  
Vol 152 (3) ◽  
pp. 407-412 ◽  
Author(s):  
M Montiel ◽  
M C Caro ◽  
E Jiménez
Keyword(s):  
Plasma Membrane ◽  
Angiotensin Ii ◽  
Binding Sites ◽  
Plasma Membranes ◽  
Binding Capacity ◽  
Rat Hepatocytes ◽  
Receptor Complex ◽  
Ang Ii ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

Angiotensin II (Ang II) provokes rapid internalisation of its receptor from plasma membranes in isolated rat hepatocytes. After 10 min stimulation with Ang II, plasma membrane lost about 60% of its 125I-Ang II-binding capacity. Internalisation was blocked by phenylarsine oxide (PhAsO), whereas okadaic acid, which markedly reduced the sustained phase of calcium mobilization, did not have a preventive effect on Ang II–receptor complex sequestration. These data suggest that Ang II receptor internalisation is probably independent of a phosphorylation/dephosphorylation cycle of critical serine/threonine residues in the receptor molecule. To establish a relationship between sequestration of the Ang II receptor and the physical properties of the Ang II-binding sites, 125I-Ang II–receptor complex profiles were analysed by isoelectric focusing. In plasma membrane preparations two predominant Ang II-binding sites, migrating to pI 6·8 and 6·5 were found. After exposure to Ang II, cells lost 125I-Ang II-binding capacity to the Ang II–receptor complex migrating at pI 6·8 which was prevented in PhAsO-treated cells. Pretreatment of hepatocytes with okadaic acid did not modify Ang II–receptor complex profiles, indicating that the binding sites corresponding to pI 6·5 and pI 6·8 do not represent a phosphorylated and/or non-phosphorylated form of the Ang II receptor. The results show that the Ang II–receptor complex isoform at pI 6·8 represents a functional form of the type-1 Ang II receptor. Further studies are necessary to identify the Ang II-related nature of the binding sites corresponding to pI 6·5. Journal of Endocrinology (1997) 152, 407–412

scholarly journals Use of digitonin extraction to distinguish between autophagic-lysosomal sequestration and mitochondrial uptake of [14C]sucrose in hepatocytes

1985 ◽  
Vol 232 (3) ◽  
pp. 773-780 ◽  
Author(s):  
P B Gordon ◽  
H Tolleshaug ◽  
P O Seglen
Keyword(s):  
Rat Hepatocytes ◽  
Amino Acid Mixture ◽  
Sugar Uptake ◽  
Acid Mixture ◽  
Detectable Effect ◽  
Isolated Rat Hepatocytes ◽  
Assay Procedure ◽  
Low Concentrations ◽  
Extraction Step ◽  
Isolated Rat

In isolated rat hepatocytes, electroinjected [14C]sucrose is sequestered both by mitochondria and by autophagosomes/lysosomes. Radioactivity can be selectively extracted from the latter organelles by low concentrations of digitonin, thereby providing a specific bioassay for autophagic sequestration. By including a digitonin extraction step in the assay procedure, autophagic [14C]sucrose sequestration could be shown to be virtually completely (greater than 90%) suppressed by the autophagy inhibitor 3-methyladenine (10 mM), whereas mitochondrial sugar uptake was unaffected. An amino acid mixture likewise suppressed autophagic sequestration very strongly, while having no detectable effect on the mitochondria.

Propranolol metabolism by isolated hepatocytes from normal and cirrhotic rat livers: the effect of albumin

1990 ◽  
Vol 68 (6) ◽  
pp. 657-662 ◽  
Author(s):  
Louise Gariepy ◽  
Daphna Fenyves ◽  
Jean-Luc Petit ◽  
Ginette Raymond ◽  
Jean-Pierre Villeneuve
Keyword(s):  
Free Fraction ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Hepatic Uptake ◽  
Albumin Concentration ◽  
Isolated Rat Hepatocytes ◽  
Subsequent Elimination ◽  
Rat Livers ◽  
Mediated Catalysis ◽  
Isolated Rat

Several recent reports have shown that the hepatic uptake and subsequent elimination of some substrates is faster in the presence of albumin than in its absence, as if some of the substrate bound to albumin was also available for uptake. In the present study, we examined the effect of albumin on the clearance of propranolol by isolated rat hepatocyte suspensions. The clearance of total drug decreased progressively as albumin concentration increased. There was also a progressive decrease in the free fraction of propranolol and the net result was an increase in the clearance of unbound drug (+50% at 40 g/L albumin). This increase was not due to an oncotic pressure effect of albumin, nor to the presence of fatty acids bound to albumin. The clearance of propranolol by isolated hepatocytes from cirrhotic rats was decreased compared with controls (−50%), and albumin also increased propranolol free clearance, albeit to a lesser extent than in control animals. Our results indicate that albumin facilitates the elimination of propranolol by hepatocytes, possibly because of surface-mediated catalysis of the albumin–propranolol complexes.Key words: propranolol clearance, albumin, isolated rat hepatocytes, cirrhosis.

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