scholarly journals Caffeine inhibits cytosolic calcium oscillations induced by noradrenaline and vasopressin in rat hepatocytes

1994 ◽  
Vol 301 (3) ◽  
pp. 737-744 ◽  
Author(s):  
L Combettes ◽  
B Berthon ◽  
M Claret
Keyword(s):  
Cyclic Amp ◽  
Single Cells ◽  
Rat Hepatocytes ◽  
Cytosolic Calcium ◽  
Inhibitory Effect ◽  
Calcium Oscillations ◽  
Direct Inhibition ◽  
Response Curves ◽  
Release Channel ◽  
Induced Changes

The effects of caffeine on agonist-induced changes in intracellular Ca2+ concentration ([Ca2+]i) were studied in single fura 2-loaded cells and suspensions of rat hepatocytes. In single cells, caffeine (5-10 mM) inhibited [Ca2+]i oscillations induced both by noradrenaline (0.1 microM) and by vasopressin (0.1 nM). Caffeine shifted the dose-response curves of the [Ca2+]i rise induced by vasopressin (0.5 to 2 nM) and noradrenaline (from 80 to 580 nM) in suspensions of liver cells loaded with quin2. This inhibitory effect of caffeine was not due to inhibition of phosphodiesterase enzymes and elevation of cyclic AMP levels, because application of 3-isobutyl-1-methylxanthine, forskolin or 8-bromo cyclic AMP had no inhibitory effect on the intracellular Ca2+ rise induced by inositol 1,4,5-trisphosphate (InsP3)-dependent agonists. We demonstrate that the inhibitory effect of caffeine may result from at least three actions of caffeine: (1) inhibition of receptor-stimulated InsP3 formation; (2) inhibition of agonist-stimulated Ca2+ influx; and (3) direct inhibition of the InsP3-sensitive Ca(2+)-release channel.

scholarly journals Inositol trisphosphate analogues selective for types I and II inositol trisphosphate receptors exert differential effects on vasopressin-stimulated Ca2+ inflow and Ca2+ release from intracellular stores in rat hepatocytes

2004 ◽  
Vol 381 (2) ◽  
pp. 519-526 ◽  
Author(s):  
Roland B. GREGORY ◽  
Rachael HUGHES ◽  
Andrew M. RILEY ◽  
Barry V. L. POTTER ◽  
Robert A. WILCOX ◽  
...  
Keyword(s):  
Single Cells ◽  
Inositol Trisphosphate ◽  
Rat Hepatocytes ◽  
Small Region ◽  
Cell Periphery ◽  
Type I ◽  
Response Curves ◽  
Maximal Stimulation ◽  
Adenophostin A ◽  
Stimulation Of

Previous studies have shown that adenophostin A is a potent initiator of the activation of SOCs (store-operated Ca2+ channels) in rat hepatocytes, and have suggested that, of the two subtypes of Ins(1,4,5)P3 receptor predominantly present in rat hepatocytes [Ins(1,4,5)P3R1 (type I receptor) and Ins(1,4,5)P3R2 (type II receptor)], Ins(1,4,5)P3R1s are required for SOC activation. We compared the abilities of Ins(1,4,6)P3 [with higher apparent affinity for Ins(1,4,5)P3R1] and Ins(1,3,6)P3 and Ins(1,2,4,5)P4 [with higher apparent affinities for Ins(1,4,5)P3R2] to activate SOCs. The Ins(1,4,5)P3 analogues were microinjected into single cells together with fura 2, and dose–response curves for the activation of Ca2+ inflow and Ca2+ release from intracellular stores obtained for each analogue. The concentration of Ins(1,4,6)P3 which gave half-maximal stimulation of Ca2+ inflow was substantially lower than that which gave half-maximal stimulation of Ca2+ release. By contrast, for Ins(1,3,6)P3 and Ins(1,2,4,5)P3, the concentration which gave half-maximal stimulation of Ca2+ inflow was substantially higher than that which gave half-maximal stimulation of Ca2+ release. The distribution of Ins(1,4,5)P3R1 and Ins(1,4,5)P3R2 in rat hepatocytes cultured under the same conditions as those employed for the measurement of Ca2+ inflow and release was determined by immunofluorescence. Ins(1,4,5)-P3R1s were found predominantly at the cell periphery, whereas Ins(1,4,5)P3R2s were found at the cell periphery, the cell interior and nucleus. It is concluded that the idea that a small region of the endoplasmic reticulum enriched in Ins(1,4,5)P3R1 is required for the activation of SOCs is consistent with the present results for hepatocytes.

scholarly journals Regulation of heparan sulphate metabolism by adenosine 3′:5′-cyclic monophosphate in hepatocytes in culture

1980 ◽  
Vol 192 (2) ◽  
pp. 395-402 ◽  
Author(s):  
Perumana R. Sudhakaran ◽  
Wolfgang Sinn ◽  
Kurt von Figura
Keyword(s):  
Cyclic Amp ◽  
Heparan Sulphate ◽  
Molecular Size ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Dibutyryl Cyclic Amp ◽  
Isolated Rat Hepatocytes ◽  
Intracellular Compartments ◽  
Sulphated Glycosaminoglycans ◽  
Chain Synthesis

Freshly isolated rat hepatocytes maintained as monolayers in a serum-free medium synthesize sulphated glycosaminoglycans, most of which behave as heparan sulphate and are mainly distributed into intracellular compartments. Cyclic AMP, dibutyryl cyclic AMP, glucagon, noradrenaline, prostaglandin E1, and theophylline, all drugs and hormones known to increase intracellular cyclic AMP concentrations, decreased the incorporation of 35SO42− into heparan sulphate of intra-, extra- and peri-cellular pools. The inhibition mediated by dibutyryl cyclic AMP was dose-dependent and observed as early as 2h after exposure to the drug. In the presence of 1mm-dibutyryl cyclic AMP, incorporation of 35SO42− or [14C]glucosamine into heparan sulphate was decreased to 40–50%, suggesting that dibutyryl cyclic AMP interfered with the synthesis of heparan sulphate. This was further supported by pulse–chase experiments, where dibutyryl cyclic AMP had no effect on the degradation of sulphated glycosaminoglycans. Heparan sulphates synthesized and secreted into the extracellular pool in the presence of dibutyryl cyclic AMP were smaller in size, whereas the degree of sulphation and molecular size of the heparan sulphate chains released by β-elimination from these proteoglycans were not different from control values. In the presence of 1mm-cycloheximide, 35SO42− incorporation was decreased to 5%. Addition of p-nitrophenyl β-d-xyloside, an artificial acceptor of glycosaminoglycan chain synthesis, enhanced this incorporation to 18%. Dibutyryl cyclic AMP did not have any inhibitory effect on the synthesis of chains initiated on p-nitrophenyl β-d-xylosides. Incorporation of [3H]serine into heparan sulphate was not affected by dibutyryl cyclic AMP, whereas the degree of substitution of serine residues with heparan sulphate chains was less in heparan sulphate synthesized in the presence of dibutyryl cyclic AMP, suggesting that cyclic AMP exerts its effect on the metabolism of sulphated glycosaminoglycans by affecting the transfer of xylose on to the protein core.

cGMP abolishes agonist-induced [Ca2+]ioscillations in human bladder epithelial cells

2001 ◽  
Vol 281 (6) ◽  
pp. F1067-F1074 ◽  
Author(s):  
H. Y. Kwan ◽  
Y. Huang ◽  
S. K. Kong ◽  
X. Yao
Keyword(s):  
Epithelial Cells ◽  
Prolonged Exposure ◽  
Specific Inhibitor ◽  
Cytosolic Calcium ◽  
Inhibitory Effect ◽  
Calcium Oscillations ◽  
Protein Kinase G ◽  
Human Bladder ◽  
Inositol 1,4,5 Trisphosphate ◽  
Intracellular Ca

First published August 9, 2001; 10.1152/ajprenal.00031.2001.—Cytosolic calcium oscillations may permit cells to respond to information provided by increases in intracellular Ca2+ concentration ([Ca2+]i ) while avoiding prolonged exposure to constantly elevated [Ca2+]i. In this study, we demonstrated that agonists could induce Ca2+oscillations in human bladder epithelial cells. Application of 10 μM acetylcholine or 200 nM bradykinin triggered an initial Ca2+ transient that was followed by periodic [Ca2+]i oscillations. The oscillations did not depend on extracellular Ca2+. 8-Bromoguanosine 3′,5′-cyclic monophosphate abolished acetylcholine- or bradykinin-induced oscillations. Elevation of cellular cGMP by dipyridamole, an inhibitor of cGMP-specific phosphodiesterase, also terminated the [Ca2+]i oscillations. The inhibitory effect of cGMP could be reversed by KT-5823, a highly specific inhibitor of protein kinase G (PKG), suggesting that the action of cGMP was mediated by PKG. Comparison of the effect of cGMP with that of xestospongin C, an inhibitor of the inositol 1,4,5-trisphosphate (IP3) receptor, revealed similarities between the action of cGMP and xestospongin C. Therefore, it is likely that cGMP and PKG may target a signal transduction step(s) linked to IP3 receptor-mediated Ca2+ release.

scholarly journals An investigation of the involvement of adenosine 3′:5′-cyclic monophosphate in steroidogenesis by using isolated adrenal cell column perfusion

1975 ◽  
Vol 148 (3) ◽  
pp. 539-544 ◽  
Author(s):  
A M Hudson ◽  
C McMartin
Keyword(s):  
Cyclic Amp ◽  
Inverse Relationship ◽  
Time Lag ◽  
Inhibitory Effect ◽  
Cell Column ◽  
Response Curves ◽  
Steroid Production ◽  
Adrenal Cell ◽  
Narrow Concentration Range ◽  
Range Variation

The involvement of cyclic AMP in corticosteroidogenesis was investigated by using isolated adrenal cell column perfusion. Steroids were produced in response to 0.5, 1.0 and 5.0 mg of cyclic AMP/ml. Analysis of the shape of the response curves indicated an inverse relationship between rate of onset of steroid production and dose. A further increase in steroid production during the washout period after the 5 mg/ml dose was considered to indicate an intracellular inhibitory effect of cyclic AMP. Release of cyclic AMP into the perfusate only occurred in response to supramaximal steroidogenic doses of ACTH (adrenocorticotrophin). A connexion between dose and response was demonstrated over a narrow concentration range. Variation in the time-lag before cyclic AMP production and in the duration of the response was marked; further, no reproducible ratio of steroid output to cyclic AMP output was shown at any level of stimulation. These results are discussed together with those of other recent investigations. It is considered that these findings do not support an obligatory role for cyclic AMP as mediator of ACTH action in the adrenal.

Antagonistic control of fluid secretion by the Malpighian tubules ofTenebrio molitor: effects of diuretic and antidiuretic peptides and their second messengers

2002 ◽  
Vol 205 (4) ◽  
pp. 493-501 ◽  
Author(s):  
U. I. M. Wiehart ◽  
S. W. Nicolson ◽  
R. A. Eigenheer ◽  
D. A. Schooley
Keyword(s):  
Cyclic Amp ◽  
Cyclic Gmp ◽  
Second Messengers ◽  
Fluid Secretion ◽  
Tenebrio Molitor ◽  
Inhibitory Effect ◽  
Malpighian Tubules ◽  
Dependent Manner ◽  
Response Curves

SUMMARYFluid secretion by insect Malpighian tubules is controlled by haemolymph-borne factors. The mealworm Tenebrio molitor provides the first known example of antagonistic interactions between endogenous neuropeptides acting on Malpighian tubules. The two corticotropin-releasing-factor (CRF)-related diuretic peptides previously isolated from Tenebrio molitor, Tenmo-DH37 and Tenmo-DH47, were found to stimulate Tenebrio molitor tubules in vitro in a dose-dependent manner with EC50 values of 0.12 nmol l–1 and 26 nmol l–1 respectively. However, no synergistic or additive effect was observed when these two peptides were tested simultaneously. We then investigated antagonism between second messengers: dose–response curves were constructed for stimulation of Tenebrio molitor tubules by cyclic AMP and their inhibition by cyclic GMP. When both cyclic nucleotides were included in the bathing Ringer, the stimulatory effect of cyclic AMP was neutralised by cyclic GMP. Similarly, the stimulatory effect of Tenmo-DH37 was reversed on addition of an antidiuretic peptide (Tenmo-ADF), which was recently isolated from Tenebrio molitor and acts via cyclic GMP. The cardioacceleratory peptide CAP2b, originally isolated from Manduca sexta, also increases intracellular cyclic GMP levels and inhibited fluid secretion by Tenebrio molitor tubules, with an EC50 value of 85 nmol l–1. This inhibitory effect was reversed by Tenmo-DH37. Endogenous diuretic and antidiuretic peptides, effective at low concentrations and acting via antagonistic second messengers, have the potential for fine control of secretion rates in the Malpighian tubules of Tenebrio molitor.

Effect of hepatocyte swelling on microtubule stability and tubulin mRNA levels

1994 ◽  
Vol 72 (1-2) ◽  
pp. 12-19 ◽  
Author(s):  
Dieter Häussinger ◽  
Barbara Stoll ◽  
Stephan vom Dahl ◽  
Panayiotis A. Theodoropoulos ◽  
Emmanuel Markogiannakis ◽  
...  
Keyword(s):  
Cell Function ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Inhibitory Effect ◽  
Cell Swelling ◽  
Mrna Levels ◽  
Microtubule Network ◽  
Isolated Rat Hepatocytes ◽  
Tubulin Mrna ◽  
Induced Changes

Incubation of isolated rat hepatocytes under conditions known to induce cell swelling caused several alterations in microtubule physiology. As shown by immunofluorescence microscopy experiments in the absence and presence of triethyllead or colchicine (two well-established microtubule inhibitors), an apparent stabilization of the microtubule network became evident in hepatocytes exposed to hypotonic (190 mosmol/L) conditions. A similar stabilizing effect was also observed upon cell swelling induced by addition of insulin (100 nmol/L) or glutamine (10 mmol/L). The differential microtubule stabilities were not attributed to a differential incorporation of the antimicrotubular agents into hepatocytes as shown by [3H]colchicine-uptake experiments. The swelling-induced alterations of microtubules may contribute to the swelling-induced changes of liver cell function: in perfused rat liver it was found that the established inhibitory effect of hypotonic cell swelling on hepatic proteolysis was largely abolished in presence of colchicine. Tubulin mRNA levels increased by 1.9-, 2.1- and 2.7-fold in isolated hepatocytes being exposed for 120 min to hypotonic medium, insulin, or glutamine, respectively. The results suggest an involvement of microtubular structures in the regulation of liver metabolism in response to alterations of the cellular hydration state.Key words: microtubules, cell swelling, glutamine, gene expression, proteolysis.

scholarly journals Adenosine Triphosphate-Evoked Cytosolic Calcium Oscillations in Human Granulosa-Luteal Cells: Role of Protein Kinase C1

2001 ◽  
Vol 86 (2) ◽  
pp. 773-777 ◽  
Author(s):  
Chen-Jei Tai ◽  
Sung Keun Kang ◽  
Peter C. K. Leung
Keyword(s):  
Protein Kinase ◽  
Calcium Influx ◽  
Purinergic Receptor ◽  
Cytosolic Calcium ◽  
Inhibitory Effect ◽  
Calcium Oscillations ◽  
Dependent Manner ◽  
Luteal Cells

ATP has been shown to modulate progesterone production in human granulosa-luteal cells (hGLCs) in vitro. After binding to a G protein-coupled P2 purinergic receptor, ATP stimulates phospholipase C. The resultant production of diacylglycerol and inositol triphosphate activates protein kinase C (PKC) and intracellular calcium [Ca2+]i mobilization, respectively. In the present study, we examined the potential cross-talk between the PKC and Ca2+ pathway in ATP signal transduction. Specifically, the effect of PKC on regulating ATP-evoked[ Ca2+]i oscillations were examined in hGLCs. Using microspectrofluorimetry, [Ca2+]i oscillations were detected in Fura-2 loaded hGLCs in primary culture. The amplitudes of the ATP-triggered [Ca2+]i oscillations were reduced in a dose-dependent manner by pretreating the cells with various concentrations (1 nm to 10μ m) of the PKC activator, phorbol-12-myristate-13-acetate (PMA). A 10 μm concentration of PMA completely suppressed 10 μm ATP-induced oscillations. The inhibitory effect occurred even when PMA was given during the plateau phase of ATP evoked [Ca2+]i oscillations, suggesting that extracellular calcium influx was inhibited. The role of PKC was further substantiated by the observation that, in the presence of a PKC inhibitor, bisindolylmaleimide I, ATP-induced[ Ca2+]i oscillations were not completely suppressed by PMA. Furthermore, homologous desensitization of ATP-induced calcium oscillations was partially reversed by bisindolylmaleimide I, suggesting that activated PKC may be involved in the mechanism of desensitization. These results demonstrate that PKC negatively regulates the ATP-evoked [Ca2+]i mobilization from both intracellular stores and extracellular influx in hGLCs and further support a modulatory role of ATP and P2 purinoceptor in ovarian steroidogenesis.

scholarly journals Inhibition of phosphatidylethanolamine synthesis by glucagon in isolated rat hepatocytes

1989 ◽  
Vol 257 (3) ◽  
pp. 645-650 ◽  
Author(s):  
L B M Tijburg ◽  
M Houweling ◽  
M J H Geelen ◽  
L M G Van Golde
Keyword(s):  
Cyclic Amp ◽  
De Novo ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Isolated Rat Hepatocytes ◽  
Ethanolamine Phosphate ◽  
Isolated Rat

Exposure of isolated rat hepatocytes to glucagon or chlorophenylthio cyclic AMP led to an inhibition of the incorporation of [1,2-14C]ethanolamine into phosphatidylethanolamine. Pulse-chase experiments and measurement of the activities of the enzymes involved in the CDP-ethanolamine pathway provided evidence that the inhibitory effect of glucagon on the synthesis de novo of phosphatidylethanolamine was not caused by a diminished conversion of ethanolamine phosphate into CDP-ethanolamine. The observations suggested that the glucagon-induced inhibition of the biosynthesis of phosphatidylethanolamine is probably due to a decreased supply of diacylglycerols, resulting in a decreased formation of phosphatidylethanolamine from CDP-ethanolamine and diacylglycerols.

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