scholarly journals Evidence that binding of CTP:phosphocholine cytidylyltransferase to membranes in rat hepatocytes is modulated by the ratio of bilayer- to non-bilayer-forming lipids

1993 ◽  
Vol 291 (2) ◽  
pp. 419-427 ◽  
Author(s):  
H Jamil ◽  
G M Hatch ◽  
D E Vance
Keyword(s):  
Phospholipase A2 ◽  
Phospholipase C ◽  
Cultured Cells ◽  
Normal Values ◽  
Common Factor ◽  
Rat Hepatocytes ◽  
Cellular Membranes ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Cellular Concentration

The mechanism by which phospholipase C (PLC) digestion of cultured cells mediates binding of CTP:phosphocholine cytidylyltransferase to cellular membranes was investigated. Incubation of choline-depleted rat hepatocytes with PLC caused a translocation of enzyme from cytosol to membranes concomitant with a decrease in the concentration of phosphatidylcholine with no effect on the concentration of other phospholipids. Removal of PLC and supplementation with choline restored the amount of phosphatidylcholine in the cells and translocated cytidylyltransferase to the cytosol. However, when phosphatidylcholine levels were decreased by incubation with phospholipase A2 (PLA2), there was no significant redistribution of cytidylyltransferase activity. With PLA2 the concentration of phosphatidylethanolamine, as well as of phosphatidylcholine, was significantly decreased. Since PLC, but not phospholipase A2, raised the cellular concentration of diacylglycerol, possibly diacylglycerol mediated the binding of cytidylyltransferase to membranes. This possibility was examined, but is unlikely, since addition of lysophosphatidylcholine to PLC-treated cells restored the concentration of phosphatidylcholine and released cytidylyltransferase into the cytosol, but did not lower diacylglycerol levels to normal values. Studies in vitro, incubations of cells with choline analogues and a survey of the literature suggested that the over-riding common factor in regulation of cytidylyltransferase binding to membranes may be the ratio of bilayer to non-bilayer lipids in that membrane.

scholarly journals Phospholipase C activation by ethanol in rat hepatocytes is unaffected by chronic ethanol feeding

1990 ◽  
Vol 272 (1) ◽  
pp. 59-64 ◽  
Author(s):  
J B Hoek ◽  
T F Taraschi ◽  
K Higashi ◽  
E Rubin ◽  
A P Thomas
Keyword(s):  
Phospholipase C ◽  
Order Parameter ◽  
Plasma Membranes ◽  
Structural Changes ◽  
Rat Hepatocytes ◽  
Maximal Response ◽  
Molecular Order ◽  
Transient Activation ◽  
Ethanol Feeding

The activation of phosphoinositide-specific phospholipase C by ethanol was compared in hepatocytes isolated from ethanol-fed rats and from pair-fed control animals. Ethanol (100-300 mM) caused a dose-dependent transient increase in cytosolic free Ca2+ levels in indo-1-loaded hepatocytes from both groups of animals. The rate of Ca2+ increase was similar in hepatocytes from control and ethanol-fed rats, but the decay of the Ca2+ increase was somewhat slower in the latter preparation. The ethanol-induced Ca2+ increase caused activation of glycogen phosphorylase, with 50% response at 50 mM-ethanol and a maximal response at 150-200 mM-ethanol, not significantly different in hepatocytes from control and ethanol-fed animals. Ins(1,4,5)P3 formation in response to ethanol (300 mM) or vasopressin (2 nM or 40 nM) was also similar in the two preparations. It is concluded that long-term ethanol feeding does not lead to an adaptive response with respect to the ethanol-induced phospholipase C activation in rat hepatocytes. The ability of ethanol in vitro to decrease membrane molecular order in liver plasma membranes from ethanol-fed and control rats was measured by e.s.r. Membranes from ethanol-fed animals had a significantly lower baseline order parameter compared with control preparations (0.313 and 0.327 respectively), indicative of decreased membrane molecular order. Addition of 100 mM-ethanol significantly decreased the order parameter in control preparations by 2.1%, but had no effect on the order parameter of plasma membranes from ethanol-fed rats, indicating that the plasma membranes had developed tolerance to ethanol, similar to other membranes in the liver. Thus the membrane structural changes associated with this membrane tolerance do not modify the ethanol-induced activation of phospholipase C. The transient activation of phospholipase C by ethanol in hepatocytes may play a role in maintaining an adaptive phenotype in rat liver.

Muscarinic Ciliostimulation Requires Endogenous Prostaglandin Production

1998 ◽  
Vol 12 (3) ◽  
pp. 203-208 ◽  
Author(s):  
Scott M. Gayner ◽  
Thomas V. McCaffrey
Keyword(s):  
Phospholipase A2 ◽  
Phospholipase C ◽  
Beat Frequency ◽  
Ciliary Beat Frequency ◽  
Pge2 Production ◽  
Ciliary Activity ◽  
Frequency Increase ◽  
Prostaglandin Production ◽  
Ciliary Beat

Prostaglandin E2 (PGE2) is a known modulator in upper airway ciliary activity and may be involved in the transduction of the muscarinic acetylcholine receptor signal. We studied the in vitro effects of muscarinic ciliostimulation on ciliary beat frequency (CBF) and PGE2 in human adenoid explants to determine whether PGE2 production is an essential step in the signal transduction mechanism. Methacholine applied to adenoid explants significantly increased ciliary beat frequency. This effect was blocked by the application of diclofenac, a cyclooxygenase inhibitor. Using radioimmunoassay, PGE2 production was measured during ciliostimulation with methacholine. Methacholine produced a significant increase in production in PGE2 during ciliostimulation. The roles of phospholipase C and phospholipase A2 in prostaglandin production were investigated by inhibiting these enzymes. D609, a phospholipase C inhibitor, significantly inhibited ciliary beat frequency increase and PGE2 production during methacholine stimulation. However, PACOCF3, a phospholipase A2 inhibitor, did not block ciliary beat frequency increase or PGE2 production in response to methacholine. These data show that phospholipase C is required for PGE2 production and ciliostimulation.

scholarly journals Exogenous phospholipase enzymes mimic effects of phenylephrine on Ca2+ transport in hepatocytes

1983 ◽  
Vol 210 (1) ◽  
pp. 115-119 ◽  
Author(s):  
G J Barritt ◽  
J A Whiting
Keyword(s):  
Plasma Membrane ◽  
Phospholipase A2 ◽  
Phospholipase C ◽  
Time Course ◽  
Initial Rate ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Glucose Release ◽  
Significant Damage ◽  
Isolated Rat

Phospholipase C from Clostridium perfringens induced the release of 45Ca2+ from isolated rat hepatocytes incubated at 0.1 mM extracellular Ca2+ with a time course similar to that for the action of phenylephrine. Under the conditions of these experiments, no significant damage to the plasma membrane was detected in the presence of phospholipase C. Little 45Ca2+ release was induced by bee venom phospholipase A2. At 1.3 mM extracellular Ca2+, both phospholipase enzymes stimulated the initial rate of 45Ca2+ exchange. Concentrations of phospholipase C comparable with those that stimulated 45Ca2+ release increased the rates of glucose release and O2 utilization by 70 and 20% respectively. An increase in the rate of O2 utilization but not glucose release was observed after the addition of phospholipase A2 to hepatocytes. The possible role for a cellular phospholipase C in the mechanism by which phenylephrine stimulates glycogenolysis in the liver cell is briefly discussed.

Silencing of phospholipase C gamma 2 promotes proliferation of rat hepatocytes in vitro

2018 ◽  
Vol 119 (5) ◽  
pp. 4085-4096
Author(s):  
Xiaoguang Chen ◽  
Xuemin Zhu ◽  
Yumei Liu ◽  
Qiongxia Lv ◽  
Jun Ma
Keyword(s):  
Phospholipase C ◽  
Rat Hepatocytes ◽  
Phospholipase C Gamma

scholarly journals Hormonal regulation of glutathione S-transferase expression in co-cultured adult rat hepatocytes

2000 ◽  
Vol 166 (2) ◽  
pp. 363-371 ◽  
Author(s):  
S Coecke ◽  
T Vanhaecke ◽  
A Foriers ◽  
IR Phillips ◽  
A Vercruysse ◽  
...  
Keyword(s):  
Hormonal Regulation ◽  
Cultured Cells ◽  
Experimental System ◽  
Human Growth ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Adult Rat ◽  
Adult Rat Hepatocytes ◽  
Translational Level

Glutathione S-transferases (GSTs) are subject to regulation by thyroid and sex hormones and by GH. We have used an in vitro experimental system comprising adult rat hepatocytes co-cultured with rat liver epithelial cells of primitive biliary origin, to distinguish between direct and indirect effects of various hormones on GSTs; to identify the GST subunits affected by individual hormones; and to investigate the level at which the hormones act. Tri-iodothyronine (T3), thyroxine (T4) and 17beta-oestradiol (OE2) reduced GST activities, whereas testosterone, dihydrotestosterone, and human growth hormone (hGH) had little effect on total GST activity. HPLC separation of the various GST subunits revealed that T3 and T4 reduced total GST content, in particular the abundance of subunits M1 and M2. The amount of the Pi-class subunit P1 was reduced by OE2. Treatment of the co-cultured cells with this hormone altered the GST subunit profile to one that is more similar to that observed in freshly isolated hepatocytes. Analysis of mRNAs demonstrated that some of the hormones act at a pre-translational level, whereas others act at a translational or post-translational level to regulate the expression of various GST subunits.

scholarly journals Head-group specificity for feedback regulation of CTP:phosphocholine cytidylyltransferase

1990 ◽  
Vol 270 (3) ◽  
pp. 749-754 ◽  
Author(s):  
H Jamil ◽  
D E Vance
Keyword(s):  
Feedback Regulation ◽  
Rat Hepatocytes ◽  
Fold Increase ◽  
Maximum Amount ◽  
Head Group ◽  
Maximal Effect ◽  
Cellular Membranes ◽  
Phosphocholine Cytidylyltransferase ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Phosphatidylcholine Biosynthesis

The specificity of the phospholipid head-group for feedback regulation of CTP: phosphocholine cytidylyltransferase was examined in rat hepatocytes. In choline-deficient cells there is a 2-fold increase in binding of cytidylyltransferase to cellular membranes, compared with choline-supplemented cells. Supplementation of choline-deficient cells with choline, dimethylethanolamine, monomethylethanolamine or ethanolamine resulted in an increase in the concentration of the corresponding phospholipid. Release of cytidylyltransferase into cytosol was only observed in hepatocytes supplemented with choline or dimethylethanolamine. The apparent EC50 values (concn. giving half of maximal effect) for cytidylyltransferase translocation were similar for choline and dimethylethanolamine (25 and 27 microM respectively). The maximum amount of cytidylyltransferase released into cytosol with choline supplementation (1.13 m-units/mg membrane protein) was twice that (0.62) observed with dimethylethanolamine. Supplementation of choline-deficient hepatocytes with NN′-diethylethanolamine, N-ethylethanolamine or 3-aminopropanol also did not cause release of cytidylyltransferase from cellular membranes. The translocation of cytidylyltransferase appeared to be mediated by the concentration of phosphatidylcholine in the membranes and not the ratio of phosphatidylcholine to phosphatidylethanolamine. The results provide further evidence for feedback regulation of phosphatidylcholine biosynthesis by phosphatidylcholine.

Immunoenzymatic demonstration of the simultaneous presence of transferrin, hemopexin and albumin in a same hepatocyte and their ultrastructural localization

1978 ◽  
Vol 36 (2) ◽  
pp. 88-89
Author(s):  
M. Kraemer ◽  
J. Foucrier ◽  
J. Vassy ◽  
M.T. Chalumeau
Keyword(s):  
Plasma Proteins ◽  
Rat Hepatocytes ◽  
Ultrastructural Localization ◽  
Carrier Proteins ◽  
Normal Cells ◽  
Adult Rat ◽  
Adult Rat Hepatocytes ◽  
Monospecific Antisera ◽  
Different Levels

Some authors using immunofluorescent techniques had already suggested that some hepatocytes are able to synthetize several plasma proteins. In vitro studies on normal cells or on cells issued of murine hepatomas raise the same conclusion. These works could be indications of an hepatocyte functionnal non-specialization, meanwhile the authors never give direct topographic proofs suitable with this hypothesis.The use of immunoenzymatic techniques after obtention of monospecific antisera had seemed to us useful to bring forward a better knowledge of this problem. We have studied three carrier proteins (transferrin = Tf, hemopexin = Hx, albumin = Alb) operating at different levels in iron metabolism by demonstrating and localizing the adult rat hepatocytes involved in their synthesis.Immunological, histological and ultrastructural methods have been described in a previous work.

Ultrastructural Correlations between Clonal Human Tumor Colonies and in Vivo Neoplasms

1982 ◽  
Vol 40 ◽  
pp. 210-211
Author(s):  
M.J. Murphy ◽  
R.R. Price ◽  
J.C. Sloman
Keyword(s):  
Cultured Cells ◽  
Human Tumor ◽  
Cell Type ◽  
Tumor Mass ◽  
Initial Cell ◽  
Cloning Assay ◽  
Human Tumor Cloning ◽  
The Relationship

The in vitro human tumor cloning assay originally described by Salmon and Hamburger has been applied recently to the investigation of differential anti-tumor drug sensitivities over a broad range of human neoplasms. A major problem in the acceptance of this technique has been the question of the relationship between the cultured cells and the original patient tumor, i.e., whether the colonies that develop derive from the neoplasm or from some other cell type within the initial cell population. A study of the ultrastructural morphology of the cultured cells vs. patient tumor has therefore been undertaken to resolve this question. Direct correlation was assured by division of a common tumor mass at surgical resection, one biopsy being fixed for TEM studies, the second being rapidly transported to the laboratory for culture.

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