scholarly journals Glycogenolytic effects of the calcium ionophore A23187, but not of vasopressin or angiotensin, in foetal-rat hepatocytes

1984 ◽  
Vol 220 (2) ◽  
pp. 441-445 ◽  
Author(s):  
M Freemark ◽  
S Handwerger
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Glycogen Synthesis ◽  
Calcium Ionophore ◽  
Rat Hepatocytes ◽  
Glycogen Metabolism ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Foetal Rat ◽  
20 Nm

Vasopressin, angiotensin and phenylephrine stimulate glycogenolysis in postnatal rat liver by a Ca2+-mediated mechanism not involving cyclic AMP. To determine whether these hormones promote glycogenolysis in foetal liver, we have examined their effects, and those of the Ca2+ ionophore A23187, on glycogen metabolism in cultured foetal-rat hepatocytes. Vasopressin and angiotensin (0.1 nM-0.1 microM) had no effects on either glycogen synthesis (as assessed by [14C]glucose incorporation into glycogen) or phosphorylase a activity. However, A23187 at 1 and 10 microM inhibited glycogen synthesis by 31.3 and 89.1% respectively (both P less than 0.001) and stimulated phosphorylase a activity by 66.9 and 184.1% respectively (both P less than 0.01). Incubation of cells in Ca2+-deficient medium attenuated the effects of 10 microM-A23187 on glycogen synthesis and abolished the effects of 1 microM-A23187. As in postnatal liver, glucagon (1 and 20 nM) and isoprenaline (1 and 10 microM), which activate adenylate cyclase, inhibited glycogen synthesis and stimulated phosphorylase a activity in foetal hepatocytes. The minimal effective concentration of phenylephrine was 10 times that of isoprenaline. These results indicate striking differences in the ontogeny of cyclic AMP-mediated and Ca2+-mediated processes which regulate hepatic glycogenolysis. Since increases in cytosolic Ca2+ induce glycogenolysis in foetal-rat liver, the weak or absent responses to vasopressin, angiotensin and the alpha-adrenergic agonists may result from defects in hormone-receptor binding or in post-receptor events leading to the mobilization of intracellular Ca2+ stores.

Mitogenesis by serum and PDGF is independent of PI degradation and PKC in VSMC

1989 ◽  
Vol 256 (4) ◽  
pp. C886-C892 ◽  
Author(s):  
M. Kihara ◽  
P. J. Robinson ◽  
S. H. Buck ◽  
R. C. Dage
Keyword(s):  
Growth Factor ◽  
Cell Growth ◽  
Growth Control ◽  
Calcium Ionophore ◽  
Rat Aorta ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Pi Turnover ◽  
Fetal Bovine ◽  
20 Nm

Capacities of serum, platelet-derived growth factor (PDGF), and fibroblast growth factor (FGF) on phosphatidylinositol (PI) degradation and cell growth were compared in cultured vascular smooth muscle cells (VSMC) from rat aorta. The role of protein kinase C (PKC) in growth control was also evaluated using polymixin B, a selective inhibitor of PKC. Both dialyzed and nondialyzed fetal bovine serum (FBS) in concentrations from 2 to 20% stimulated [3H]thymidine incorporation into DNA and cell growth without producing corresponding increases in PI turnover. Moreover, both PDGF (40-160 ng/ml) and FGF (6.25-150 ng/ml) also stimulated mitogenesis, but PDGF was more effective although less potent. Mitogenic amounts of PDGF did not stimulate PI turnover, whereas a maximally mitogenic amount of FGF (50 ng/ml) did produce a slight increase. Polymixin B inhibited PKC activity (IC50, 32 microM) from these cells but failed to suppress DNA synthesis produced by 10% FBS or PDGF (50 ng/ml). However, it did suppress that by FGF (50 ng/ml). Angiotensin II (10(-11)-10(-7) M) and phorbol 12,13-dibutyrate (PDB, 1-20 nM) were not mitogenic in the presence or absence of insulin (10 micrograms/ml) or the calcium ionophore A23187 (0.25-4 microM), under serum-free conditions. Instead, PDB inhibited mitogenesis of cells maintained under 0.2% FBS or stimulated with insulin (10 micrograms/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential control of type-I iodothyronine deiodinase expression by the activation of the cyclic AMP and phosphoinositol signalling pathways in cultured human thyrocytes

1995 ◽  
Vol 14 (2) ◽  
pp. 171-177 ◽  
Author(s):  
S G Beech ◽  
S W Walker ◽  
J R Arthur ◽  
D Lee ◽  
G J Beckett
Keyword(s):  
Cyclic Amp ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Signalling Pathways ◽  
Cell Labelling ◽  
Ionophore A23187 ◽  
Type I ◽  
Iodothyronine Deiodinase ◽  
Differential Control ◽  
Stimulation Of

ABSTRACT The effects of TSH and the activation of the cyclic AMP (cAMP) and Ca2+-phosphatidylinositol (Ca2+-PI) cascades on the activity and expression of the selenoenzyme thyroidal type-I iodothyronine deiodinase (ID-I) have been studied using human thyrocytes grown in primary culture. Stimulation of ID-I activity and expression was obtained with TSH and an analogue of cAMP, 8-bromo-cAMP. In the presence or absence of TSH, the addition of the phorbol ester, phorbol 12-myristate 13-acetate (PMA) together with the calcium ionophore A23187, caused a decrease in ID-I activity; a decrease in ID-I expression was also observed as assessed by cell labelling with [75 Se]selenite. PMA alone had no effect on ID-I activity in the presence or absence of TSH. A23187 alone produced a small but significant reduction in ID-I activity, but only in TSH-stimulated cells. These data provide evidence that the expression of thyroidal ID-I is negatively regulated by the Ca2+-PI cascade, and positively regulated by the cAMP cascade.

An investigation of the involvement of calcium in the control of prolactin secretion: studies with low calcium, methoxyverapamil, cobalt and manganese

1984 ◽  
Vol 101 (3) ◽  
pp. 319-325 ◽  
Author(s):  
J. E. Merritt ◽  
B. L. Brown
Keyword(s):  
Cyclic Amp ◽  
Phosphodiesterase Inhibitor ◽  
Calcium Ionophore ◽  
Prolactin Secretion ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Pituitary Cells ◽  
Thyrotrophin Releasing Hormone ◽  
Voltage Dependent

ABSTRACT The possible role of calcium as a primary mediator in the control of prolactin secretion from normal pituitary cells was examined. Basal prolactin secretion, and secretion stimulated by thyrotrophin releasing hormone (TRH), raised K + or the calcium ionophore, A23187, were all dependent on the presence of extracellular Ca2+. The calcium channel antagonists, methoxyverapamil, cobalt and manganese, inhibited basal, TRH- and K+-stimulated prolactin secretion. In addition, prolactin secretion stimulated by a phosphodiesterase inhibitor, isobutylmethylxanthine, which increases cellular cyclic AMP, was inhibited by these Ca2+ antagonists. These observations indicate that Ca2+ may be the primary intracellular mediator in the control of prolactin secretion, with cyclic AMP having a secondary modulatory role on Ca2+ influx, probably on voltage-dependent Ca2+ channels. J. Endocr. (1984) 101, 319–325

cAMP-independent stimulation of glycogen phosphorylase in newborn rat hepatocytes

1985 ◽  
Vol 248 (5) ◽  
pp. E560-E566
Author(s):  
A. Noguchi ◽  
P. A. Jett ◽  
A. H. Gold
Keyword(s):  
Glycogen Phosphorylase ◽  
Calcium Ionophore ◽  
Rat Hepatocytes ◽  
Calcium Ionophore A23187 ◽  
Membrane Receptors ◽  
Ionophore A23187 ◽  
Adrenergic Stimulation ◽  
Adult Rats ◽  
Isolated Rat Hepatocytes ◽  
Beta Adrenergic

Postnatal development of glycogen phosphorylase activation by the cAMP-independent pathway was examined in isolated rat hepatocytes from control and propylthiouracil-treated congenital hypothyroid rat pups. At 5 days postnatum there was complete phosphorylase activation by beta-adrenergic stimulation, glucagon, and the calcium ionophore A23187, but no activation by alpha-adrenergic stimulation. Activation of phosphorylase by angiotensin or vasopressin was less than in hepatocytes from adult rats (P less than 0.01). At 28 days postnatum activation by all of these hormones was complete. In the propylthiouracil-treated group hormone responsiveness was similar to the control at 5 days postnatum. However, alpha-adrenergic (P less than 0.025), angiotensin, and vasopressin (P less than 0.05) activation was decreased at 28 days postnatum, and beta-adrenergic, glucagon, and A23187 activation was complete. The attenuated responses were restored by thyroxine replacement from 15 days postnatum. [32P]Pi incorporation into phosphatidylinositol by epinephrine and vasopressin in 28-day propylthiouracil-treated rats was lower than the control (P less than 0.01). We speculate that the diminished phosphorylase response of hepatocytes to alpha-adrenergic, vasopressin, or angiotensin stimuli in the early neonatal period could be related to low receptor numbers and the weaker phosphoinositide response during this period. Also, the depressed phosphorylase response to alpha-adrenergic, vasopressin, and angiotensin stimulation in congenital hypothyroidism at 28 days postnatum could be related to a decrease in number of plasma membrane receptors for these agonists.

scholarly journals The calcium ionophore A23187 increases the tight-junctional permeability in rat liver

1988 ◽  
Vol 256 (3) ◽  
pp. 1039-1041 ◽  
Author(s):  
K S Kan ◽  
R Coleman
Keyword(s):  
Horseradish Peroxidase ◽  
Rat Liver ◽  
Bile Flow ◽  
Calcium Ionophore ◽  
Peak Height ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Hepatocellular Damage ◽  
Junctional Permeability ◽  
Second Peak

The effect of an increase in intracellular Ca2+ concentration on tight-junctional permeability in rat liver was studied by using the calcium ionophore A23187. Infusion of 100 microliters of dimethyl sulphoxide containing various amounts of A23187 over 30 min into isolated perfused livers was followed by a pulse of horseradish peroxidase (HRP) under single-pass conditions. The first biliary HRP peak, a measure of junctional permeability, was increased 4-fold with 100 micrograms of A23187. There were, however, no significant effects on bile flow or on aspartate aminotransferase leakage as compared with the control at this dosage, and thus the increase in junctional permeability was occurring without evidence of appreciable cholestatic or hepatocellular damage. Higher dosages of A23187, however, caused not only an increase in HRP peak height but also changes in bile flow and increases in aminotransferase leakage, indicating more extensive effects at these higher dosages. A second peak of HRP secretion, occurring 20-25 min after the HRP pulse, was also elevated approx. 3.5-fold; this may indicate that pinocytosis and transcellular movement of HRP are also increased under these conditions.

Phospholipid metabolism and intracellular Ca2+ homeostasis in cultured rat hepatocytes intoxicated with cyanide

1992 ◽  
Vol 263 (3) ◽  
pp. C684-C690 ◽  
Author(s):  
I. Sakaida ◽  
A. P. Thomas ◽  
J. L. Farber
Keyword(s):  
Cytochalasin B ◽  
Calcium Ionophore ◽  
Rat Hepatocytes ◽  
Phospholipid Metabolism ◽  
Calcium Ionophore A23187 ◽  
Free Calcium ◽  
Ionophore A23187 ◽  
Cultured Hepatocytes ◽  
Extracellular Acidosis ◽  
Phospholipid Degradation

The killing of cultured hepatocytes by 1 mM sodium cyanide was reduced by 100 microM chlorpromazine or cytochalasin B (25 micrograms/ml) or by lowering the pH of the culture medium to 6.0. In each case, ATP was depleted despite the decreased number of dead cells. The cell killing by cyanide was accompanied by an accelerated release of 3H-labeled arachidonate from phospholipids. Depletion of ATP by oligomycin did not accelerate phospholipid degradation or kill the hepatocytes. Chlorpromazine, cytochalasin B, and extracellular acidosis reduced the rate of phospholipid degradation in control cells as well as the increase that occurred with cyanide. The calcium ionophore A23187 increased phospholipid degradation and killed the hepatocytes. Chlorpromazine and extracellular acidosis, but not cytochalasin B, protected the cells and prevented the increased lipid degradation in response to A23187. After addition of cyanide, cytosolic free calcium ([Ca2+]i) did not change for 71 +/- 8 min, at which time it rose to a plateau of 683 +/- 210 nM within 10 min. A second and larger rise occurred after 84 +/- 8 min and before the death of the cells at 89 +/- 8 min. Treatment with 3.5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, as well as removal of extracellular calcium, prevented these late increases in [Ca2+]i without affecting the loss of viability. It is concluded that cyanide kills cultured hepatocytes by a mechanisms that is likely related to an accelerated degradation of phospholipids. This change in lipid metabolism is not mediated by a rise in [Ca2+]i but rather may relate to an alteration in the interaction between the cytoskeleton and the plasma membrane.

Cyclic AMP and calcium in mouse mammary tumour virus expression: effects and post-transcriptional site of action

1990 ◽  
Vol 5 (1) ◽  
pp. 27-31 ◽  
Author(s):  
F. F. Bolander ◽  
M. E. Blackstone ◽  
B. M. Bradham
Keyword(s):  
Cyclic Amp ◽  
Second Messengers ◽  
Calcium Ionophore ◽  
Mammary Epithelium ◽  
Calcium Ionophore A23187 ◽  
Mammary Tumour ◽  
Ionophore A23187 ◽  
Mouse Mammary Tumour Virus ◽  
Low Concentrations ◽  
Virus Expression

ABSTRACT The role of cyclic AMP (cAMP), calcium, calmodulin and protein kinase C (PKC) in the expression of both mouse mammary tumour virus (MMTV) RNA and an MMTV glycoprotein, gp58, was investigated in normal mammary epithelium in culture. None of these second messengers had any effect on MMTV RNA. Dibutyryl cAMP alone had no effect on gp58 levels but, at low concentrations (0·05–0·1 mm), it nearly doubled the induction seen with insulin, cortisol and prolactin; higher concentrations were inhibitory. Although a calcium ionophore (A23187), either alone or with hormones, was ineffective, a calcium channel blocker (verapamil) reduced hormonal induction of gp58 by 80%, and a calmodulin inhibitor (W-13) reduced it by 90%. Two PKC activators, a phorbol ester and a diacylglyceride, were ineffective alone, with hormones or with the calcium ionophore. The following conclusions can be made: (1) cAMP, calcium and calmodulin play an important role in MMTV expression, (2) these second messengers all act post-transcriptionally, since they do not affect MMTV RNA, and (3) PKC does not appear to have a role in MMTV production in normal mammary epithelium.

scholarly journals Cystine transport in purified rat liver lysosomes

1986 ◽  
Vol 236 (3) ◽  
pp. 671-677 ◽  
Author(s):  
A J Jonas
Keyword(s):  
Rat Liver ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Proton Pumping ◽  
Proton Gradient ◽  
Ionophore A23187 ◽  
Ph Gradients ◽  
Bivalent Cations ◽  
Liver Lysosomes ◽  
Rat Liver Lysosomes

Amino acid efflux from highly purified rat liver lysosomes exposed to the methyl ester derivatives of leucine, methionine, tyrosine and cystine was examined. The lysosomal efflux of leucine, methionine and tyrosine was unaffected by the presence of MgATP, whereas cystine efflux was stimulated by MgATP. Exposure of lysosomes to 2 mM-MgATP resulted in lysosomal acidification and a 0.5 pH unit increase in the lysosomal pH gradient through the action of a proton-pumping ATPase. Cystine efflux was also stimulated when the lysosomal proton gradient was increased through changes in buffer pH. Decreasing the lysosomal proton gradient with ionophores resulted in diminished cystine efflux. Bivalent cations had no effect on the lysosomal efflux of leucine, methionine and tyrosine. However, cystine efflux was stimulated by the presence of bivalent cations even when the lysosomal proton gradient was minimized. Cation-stimulated cystine efflux was inhibited by the presence of the calcium ionophore A23187, which altered the lysosomal membrane potential. Cystine efflux from lysosomes appears to be uniquely dependent on pH gradients and cation concentrations.

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