scholarly journals Prostaglandins and muscarinic agonists induce cyclic AMP attenuation by two distinct mechanisms in the pregnant-rat myometrium. Interaction between cyclic AMP and Ca2+ signals

1990 ◽  
Vol 271 (3) ◽  
pp. 667-673 ◽  
Author(s):  
O Goureau ◽  
Z Tanfin ◽  
S Harbon
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Pertussis Toxin ◽  
Inositol Phosphates ◽  
Indirect Evidence ◽  
Maximal Response ◽  
Muscarinic Agonist ◽  
Phosphodiesterase Activity ◽  
Pregnant Rat ◽  
Cyclic Amp Accumulation

In pregnant-rat myometrium (day 21 of gestation), isoprenaline-induced cyclic AMP accumulation, resulting from receptor-mediated activation of adenylate cyclase, was negatively regulated by prostaglandins [PGE2, PGF2 alpha; EC50 (concn. giving 50% of maximal response) = 2 nM] and by the muscarinic agonist carbachol (EC50 = 2 microM). PG-induced inhibition was prevented by pertussis-toxin treatment, supporting the idea that it was mediated by the inhibitory G-protein Gi through the inhibitory pathway of the adenylate cyclase. Both isoprenaline-induced stimulation and PG-evoked inhibition of cyclic AMP were insensitive to Ca2+ depletion. By contrast, carbachol-evoked attenuation of cyclic AMP accumulation was dependent on Ca2+ and was insensitive to pertussis toxin. The inhibitory effect of carbachol was mimicked by ionomycin. Indirect evidence was thus provided for the enhancement of cyclic AMP degradation by a Ca2(+)-dependent phosphodiesterase activity in the muscarinic-mediated effect. The attenuation of cyclic AMP elicited by carbachol coincided with carbachol-stimulated inositol phosphate (InsP3, InsP2 and InsP) generation, which displayed an almost identical EC50 (3 microM) and was similarly unaffected by pertussis toxin. Both carbachol effects were reproduced by oxotremorine, whereas pilocarpine (a partial muscarinic agonist) failed to induce any decrease in cyclic AMP accumulation and concurrently was unable to stimulate the generation of inositol phosphates. These data support our proposal for a carbachol-mediated enhancement of a Ca2(+)-dependent phosphodiesterase activity, compatible with the rises in Ca2+ associated with muscarinic-induced increased generation of inositol phosphates. They further illustrate that a cross-talk between the two major transmembrane signalling systems contributed to an ultimate decrease in cyclic AMP in the pregnant-rat myometrium near term.

scholarly journals Cross-talk between glucagon- and adenosine-mediated signalling systems in rat hepatocytes: effects on cyclic AMP-phosphodiesterase activity

1995 ◽  
Vol 312 (3) ◽  
pp. 763-767 ◽  
Author(s):  
M Robles-Flores ◽  
G Allende ◽  
E Piña ◽  
J A García-Sáinz
Keyword(s):  
Cyclic Amp ◽  
Pertussis Toxin ◽  
Plasma Membranes ◽  
Rat Hepatocytes ◽  
Dependent Manner ◽  
Phosphodiesterase Activity ◽  
Cyclic Amp Phosphodiesterase ◽  
Cyclic Amp Accumulation ◽  
A1 Adenosine Receptors ◽  
Dose Dependent

The effect of adenosine analogues on glucagon-stimulated cyclic AMP accumulation in rat hepatocytes was explored. N6-Cyclopentyladenosine (CPA), 5′-N-ethylcarboxamidoadenosine and N6-(R-phenylisopropyl)adenosine inhibited in a dose-dependent manner the cyclic AMP accumulation induced by glucagon. This effect seems to be mediated through A1 adenosine receptors. Pertussis toxin completely abolished the effect of CPA on glucagon-stimulated cyclic AMP accumulation in whole cells which suggested that a pertussis-toxin-sensitive G-protein was involved. On the other hand, this action of adenosine analogues on glucagon-induced cyclic AMP accumulation was reverted by the selective low-Km cyclic AMP-phosphodiesterase inhibitor Ro 20-1724. Analysis of cyclic AMP-phosphodiesterase activity in purified hepatocyte plasma membranes showed that glucagon in the presence of GTP inhibited basal PDE activity by 45% and that CPA reverted this inhibition in dose-dependent manner. In membranes derived from pertussis-toxin-treated rats, we observed no inhibition of cyclic AMP-phosphodiesterase activity by glucagon in the absence or presence of CPA. Our results indicate that in hepatocyte plasma membranes, stimulation of adenylate cyclase activity and inhibition of a low-Km cyclic AMP phosphodiesterase activity are co-ordinately regulated by glucagon, and that A1 adenosine receptors can inhibit glucagon-stimulated cyclic AMP accumulation by blocking glucagon's effect on phosphodiesterase activity.

scholarly journals Parathyroid hormone induces protein kinase C but not adenylate cyclase in adult cardiomyocytes and regulates cyclic AMP levels via protein kinase C-dependent phosphodiesterase activity

1995 ◽  
Vol 310 (2) ◽  
pp. 439-444 ◽  
Author(s):  
K D Schlüter ◽  
M Weber ◽  
H M Piper
Keyword(s):  
Protein Kinase C ◽  
Parathyroid Hormone ◽  
Protein Kinase ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Phosphodiesterase Activity ◽  
Beta Adrenoceptor ◽  
Kinase C ◽  
Adult Cardiomyocytes ◽  
Cyclic Amp Accumulation

Adult ventricular cardiomyocytes have been identified as target cells for parathyroid hormone (PTH) but little is known about its signal transduction in these cells. In the present study the influence of PTH on cyclic AMP accumulation and the activity of protein kinase C (PKC) in cardiomyocytes was evaluated. A mid-regional synthetic fragment of PTH, PTH-(28-48), which exerts a hypertrophic effect on cardiomyocytes, increased the activity of membrane-associated PKC in a dose-dependent manner (1-100 nM). Activated membranous PKC was dependent on Ca2+ and sensitive to an inhibitor of Ca(2+)-dependent isoforms of PKC. When adenylate cyclase was stimulated by the addition of isoprenaline, a beta-adrenoceptor agonist, PTH-(28-48) antagonized cyclic AMP accumulation. This antagonistic effect of PTH-(28-48) could be mimicked by activation of PKC with a phorbol ester and inhibited by isobutylmethylxanthine, a phosphodiesterase inhibitor. An N-terminal synthetic fragment, PTH-(1-34), which includes an adenylate cyclase-activating domain, did not stimulate the accumulation of cyclic AMP in cardiomyocytes. The results demonstrate that in adult cardiomyocytes PTH (1) is able to stimulate PKC, (2) is not able to cause accumulation of cyclic AMP and (3) functionally antagonizes the effect of beta-adrenoceptor stimulation to increase cellular cyclic AMP concentrations via PKC-dependent phosphodiesterase activity.

scholarly journals Influence of bacterial toxins and forskolin upon vasopressin-induced inositol phosphate accumulation in WRK 1 cells

1989 ◽  
Vol 260 (3) ◽  
pp. 665-672 ◽  
Author(s):  
G Guillon ◽  
M N Balestre ◽  
C Lombard ◽  
F Rassendren ◽  
C J Kirk
Keyword(s):  
Cyclic Amp ◽  
Cholera Toxin ◽  
Pertussis Toxin ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Binding Capacity ◽  
Specific Binding ◽  
Phosphate Accumulation ◽  
Cyclic Amp Accumulation ◽  
Inositol Phosphate Accumulation

The accumulation of inositol phosphates in WRK 1 cells, stimulated with a range of vasopressin concentrations, was diminished by prior exposure to cholera toxin or forskolin, whilst that observed in the presence of maximal concentrations of the hormone was enhanced in pertussis-toxin-treated cells. In the presence of [32P]NAD+, both cholera toxin and pertussis toxin provoked the labelling of peptides with approximate Mrs of 45,000 and 41,000 respectively in the membranes of WRK 1 cells. Exposure to cholera toxin or forskolin for 15-18 h enhanced cyclic AMP accumulation in these cells. The concentrations of these agents which provoked half-maximal cyclic AMP accumulation were similar to those required to diminish receptor-mediated inositol phosphate accumulation by 50%. In contrast, half-maximal ADP-ribosylation of the 45,000Mr peptide needed 100-fold greater concentrations of the toxin than were effective in provoking half-maximal inhibition of inositol phosphate accumulation. Cholera toxin or forskolin also reduced the maximal specific binding, to intact WRK 1 cells, of both [3H][Arg8]vasopressin and the V1a antagonist [3H][beta-mercapto-beta,beta-cyclopentamethylenepropionic acid,O-methyl-Tyr2, Arg8]vasopressin. The kinetics for the loss of this binding capacity following cholera-toxin treatment were very similar to those describing the diminution of vasopressin-stimulated inositol phosphate accumulation in the same cells.

scholarly journals Regulation of GH3 pituitary tumour-cell adenylate cyclase activity by activators of protein kinase C

1989 ◽  
Vol 262 (3) ◽  
pp. 829-834 ◽  
Author(s):  
L A Quilliam ◽  
P R M Dobson ◽  
B L Brown
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Maximal Response ◽  
Kinase C ◽  
Cyclic Amp Accumulation ◽  
Stimulation Of

The influence of protein kinase C (PKC) activation on cyclic AMP production in GH3 cells has been studied. The stimulation of cyclic AMP accumulation induced by forskolin and cholera toxin was potentiated by 4 beta-phorbol 12,13-dibutyrate (PDBu). Moreover, PDBu, which causes attenuation of the maximal response to vasoactive intestinal polypeptide (VIP), also induced a small right shift in the dose-response curve for VIP-induced cyclic AMP accumulation. PDBu-stimulated cyclic AMP accumulation was unaffected by pretreatment of cells with pertussis toxin or the inhibitory muscarinic agonist, oxotremorine. PDBu stimulation of adenylate cyclase activity required the presence of a cytosolic factor which appeared to translocate to the plasma membrane in response to the phorbol ester. The diacylglycerol-generating agents thyroliberin, bombesin and bacterial phospholipase C each stimulated cyclic AMP accumulation, but, unlike PDBu, did not attenuate the stimulation induced by VIP. These results suggest that PKC affects at least two components of the adenylate cyclase complex. Stimulation of cyclic AMP accumulation is probably due to modification of the catalytic subunit, whereas attenuation of VIP-stimulated cyclic AMP accumulation appears to be due to the phosphorylation of a different site, which may be the VIP receptor.

scholarly journals Parathyroid hormone and prostaglandin E2 stimulate both inositol phosphates and cyclic AMP accumulation in mouse osteoblast cultures

1988 ◽  
Vol 252 (1) ◽  
pp. 263-268 ◽  
Author(s):  
R W Farndale ◽  
J R Sandy ◽  
S J Atkinson ◽  
S R Pennington ◽  
S Meghji ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Prostaglandin E2 ◽  
Intracellular Calcium ◽  
Bone Cells ◽  
Inositol Phosphates ◽  
Bone Matrix ◽  
Bone Cell ◽  
Cyclic Amp Accumulation

Parathyroid hormone (PTH) and prostaglandin E2 (PGE2) are physiological agonists which stimulate bone cells to resorb bone, a process by which the mineralized extracellular bone matrix is dissolved. Bone resorption has a key role in the maintenance of plasma calcium levels. It has been established that both PTH and PGE2 activate adenylate cyclase in osteoblasts, but it is apparent that (1) the two agents have qualitatively different effects on osteoblasts, and (2) the generation of cyclic AMP cannot account for all the effects of PTH on bone cell metabolism. Others have demonstrated that PTH and PGE2 may also elevate intracellular calcium levels, but the mechanism by which this is achieved has not been fully defined. Here we have investigated the effects of PTH on neonatal mouse osteoblasts in culture and shown that physiological concentrations of the hormone (50 nM) caused a small increase (22%) in total inositol phosphates accumulation, with a larger increase (40%) in inositol trisphosphate. We found that this activation occurred at lower concentration than was necessary to activate adenylate cyclase. PGE2 was a more effective activator of inositol phosphates accumulation than PTH, causing up to 300% increase in the total inositol phosphates after 30 min. Both PTH and PGE2 stimulated cyclic AMP accumulation, but the activation of adenylate cyclase by forskolin did not enhance inositol phosphates production. We conclude that both PTH and PGE2 stimulate phosphoinositide turnover in mouse osteoblasts and suggest that this mechanism may contribute to their elevation of intracellular calcium in bone cells.

Induction And Potentiation Of Platelet Aggregation By Clonidine And 7ρ-Aminoclonidine, Partial Agonists Of The α2-Receptor Which Regulates Platelet Adenylate Cyclase

1981 ◽  
Author(s):  
David C Stump ◽  
Donald E Macfarlane
Keyword(s):  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Specific Binding ◽  
Phase 1 ◽  
Intrinsic Activity ◽  
Second Phase ◽  
Adrenergic Agents ◽  
Cyclic Amp Accumulation ◽  
Induced Aggregation

Epinephrine induces platelet aggregation, potentiates aggregation by other agents, and blocks the stimulation of the adenylate cyclase by prostaglandins. Synthetic α-adrenergic agents have not been shown to induce aggregation. The effects of clonidine, an α2-agonist, and ρ-aminoclonidine on platelets were examined. Clonidine potentiated aggregation induced by 0.5μM ADP by 1.4-fold (1/2 max 0.5μM). It did not induce significant aggregation itself, and it inhibited aggregation induced by 5μM epinephrine (1/2 max lμM). It inhibited cyclic AMP accumulation induced by PGE1 by a maximum of 25% (1/2 max O.lμM) and it blocked inhibition by epinephrine. No significant specific binding of [3H] clonidine was observed to intact platelets. ρ-Aminoclonidine induced aggregation with delayed second phase (1/2 max 0.2μM), and potentiated ADP aggregation by 2-fold (1/2 max 0.2μM). Aggregation induced by epinephrine was more rapid, and was partially inhibited by ρ-aminoclonidine. It inhibited cyclic AMP accumulation by 50% max (1/2 max O.lμM) and attenuated epinephrine’s effect to the same level. The direct effects of ρ-aminoclonidine were blocked by lμM yohimbine, a selective α2-antagonist. Both clonidine and ρ—aminoclonidine blocked the specific binding of [3H]yohimbine (1/2 max 0.5μM). These results suggest that the platelet bears an α2-receptor with affinity for epinephrine, ρ-aminoclonidine and clonidine as agonists but that these agents display differing intrinsic activity and/or receptor reserve.

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