scholarly journals High concentrations of exogenous arachidonate inhibit calcium mobilization in platelets by stimulation of adenylate cyclase

1988 ◽  
Vol 253 (1) ◽  
pp. 255-262 ◽  
Author(s):  
M A Kowalska ◽  
A K Rao ◽  
J Disa
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Inhibitory Effect ◽  
Irreversible Damage ◽  
Fura 2 ◽  
Messenger Molecules ◽  
Thromboxane Production ◽  
High Concentrations ◽  
Stimulation Of

1. Exposure of platelets to exogenous arachidonic acid results in aggregation and secretion, which are inhibited at high arachidonate concentrations. The mechanisms for this have not been elucidated fully. In our studies in platelet suspensions, peak aggregation and secretion occurred at 2-5 microM-sodium arachidonate, with complete inhibition around 25 microM. 2. In platelets loaded with quin2 or fura-2, the cytoplasmic Ca2+ concentration, [Ca2+]i, rose in the presence of 1 mM-CaCl2 from 60-80 nM to 300-500 nM at 2-5 microM-arachidonate, followed by inhibition to basal values at 25-50 microM. Thromboxane production was not inhibited at 25 microM-arachidonate. Cyclic AMP increased in the presence of theophylline, from 3.5 pmol/10(8) platelets in unexposed platelets to 8 pmol/10(8) platelets at 50 microM-arachidonate; all platelet responses were inhibited with doubling of cyclic AMP contents. 3. The adenylate cyclase inhibitor 2′,5′-dideoxyadenosine attenuated the inhibitory effect of arachidonate, suggesting that it is mediated by increased platelet cyclic AMP and that it is unlikely to be due to irreversible damage to platelets. 4. Aspirin or the combined lipoxygenase/cyclo-oxygenase inhibitor BW 755C did not prevent the inhibition by arachidonate of either [Ca2+]i signals or aggregation induced by U46619. 5. Thus high arachidonate concentrations inhibit Ca2+ mobilization in platelets, and this is mediated by stimulation of adenylate cyclase. High arachidonate concentrations influence platelet responses by modulating intracellular concentrations of two key messenger molecules, cyclic AMP and Ca2+.

HIGH CONCENTRATIONS OF EXOGENOUS ARACHIDONATE INHIBIT CALCIUM MOBILIZATION IN PLATELETS

1987 ◽  
Author(s):  
M A Kowalska ◽  
A K Rao ◽  
J Disa
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Adenylate Cyclase ◽  
Calcium Concentration ◽  
Platelet Inhibition ◽  
Cyclooxygenase Inhibitor ◽  
Messenger Molecules ◽  
High Concentrations ◽  
Camp Levels ◽  
Stimulation Of

Exogenous arachidonic acid (AA) induces platelet aggregation and secretion which are inhibited at higher AA concentrations.To define the mechanisms for platelet inhibition at high AA,we studied the effect of itS2$odium salt on cytoplasmic ionized calcium concentration [Ca ]i, a key modulator of several platelet responses. In platelets suspended in Hepes buffer containing no albumin, peak aggregation and secretion occurred at 2-5 pM AA with partial inhibition above 10-15 pM AA and complete inhj^ition around 25-50 pM AA. In platelets ^aded with quin2, [Ca+2 ]i rose, in presence of 1 mM external Ca , from basal levels of 70-80 nM to peak of 300-500 nM at 2-5 μM AA; this was followed by inhibition to basal levels at 25-50 μM AA. At these AA concentrations there was no cell lysis. Thromboxane B. production, measured using a radioimmunoassay, was not inhibited even at 25 pM AA. Elevated celjlar levels of cAMP inhibit platelet responses including Ca2+ signals and were therefore measured using a radioimmunoassay. Platelet cAMP levels rose, in the presence of theophylline (7mM), from basal levels of 3.4 pmol/102+ plat to 5.5 at 5 μM AA and to 6.8 pmol/108 plat at 50 pM AA; Ca signals, aggregation, and secretion were inhibited with doubling of cAMP levels. On incubation of platelets with adenylate cyclase inhibitor, 2'5' dideoxgdenosine (DDA, 200 μM, 2 min) there was enhancement of peak [Ca +2]and aggregation noted with 15 pM AA; at 25 μM AA peak [Ca2+ ]i rose from 126 nM to 205 nM and aggregation was restored. Incubation with SQ 22,536 (500 μM, 5min), another adenylate cyclase inhibitor, also attenuated the inhibition by high AA levels. Treatment of platelets with aspirin or_BW 755C, a combined lipooxygenase/cyclooxygenase inhibitor, did not pryent the inhibition by high AA levels of aggregation and Ca responses induced by thromboxane analog, U46619 In conclusion, high AA concentrations inhibit cytoplasmic Ca+2 mobilization in platelets which is related to elevation of platelet cAMP through stimulation of adenylate cyclase. We propose that high AA levels inhibit aggravation and secretion by modulating cytoplasmic levels of Ca2+ and cAMP, two major messenger molecules in platelets.

Evidence for Two Separate Receptors Mediating The Stimulation of Platelet Adenylate Cyclase By Prostaglandin I2 (PGI2), PGD2 and PGE1

1979 ◽  
Author(s):  
D. C. B. Mils ◽  
D. E. Macfarlane
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Partial Agonist ◽  
Human Platelets ◽  
Intrinsic Activity ◽  
High Dose ◽  
Prostaglandin I2 ◽  
Subsequent Response ◽  
High Concentrations ◽  
Stimulation Of

Prostacyclin (PGI2), and prostaglandins D2 and E1, all inhibit aggregation of human platelets by stimulating adenylate cyclase. in platelets prelabelled with l4C adenine, PGI2 has a higher intrinsic activity than either PGD2 or PGE1, as well as a higher apparent affinity. PGE1 but not PGD2, inhibits the action of high concentrations of PGI2, both when added simultaneously with PGI2 and when added 3 min later. in the latter case the slow spontaneous fall in intracellular cyclic AMP is accelerated by PGE. but not by PGD2. PGF1α, at concentrations up to 100 μM neither stimulated the cyclase 1 by itself, nor did it inhibit the effects of PGI2, PGE1, or PGD2. PGF2α, which did cause a small increase in cyclic AMP, inhibited PGD2 strongly, PGE1 not at all, and PGI2 slightly at high concentrations. N0164, an inhibitor of aggregation induced by bis-enoic prostaglandins, inhibited cyclase stimulation by PGD2 but not by PGE1, PGE2, PGD1 or PGI2, though it reduced PGI2-induced inhibition of platelet aggregation. Preaddition of PGE1, but not of PGI2 or PGD2, at submaximal concentrations, inhibited subsequent response to high dose PGI2. The results suggest that PGE1 and PGD2 probably act on the same enzyme, but through a different receptor. PGE1 acts as a partial agonist for the receptor for PGI2, but in addition causes a tachyphylaxis not seen with PGI2 or with PGD2.

Evidence for two Separate Receptors Mediating the Stimulation of Platelet Adenylate Cyclase by Prostaglandin I2 (PCI2), PGD2 and PCE1

1979 ◽  
Author(s):  
D.C.B. Mills ◽  
D.E. Macfarlane
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Partial Agonist ◽  
Human Platelets ◽  
Intrinsic Activity ◽  
High Dose ◽  
Prostaglandin I2 ◽  
Subsequent Response ◽  
High Concentrations ◽  
Stimulation Of

Prostacyclin (PGI2), and prostaglandins D2 and E1, all inhibit aggregation of human platelets by stimulating adenylate cyclase. In platelets prelabelled with 14C adenine, PGI2 has a higher intrinsic activity than either PGD2 or PGE1α, as well as a higher apparent affinity. PGE1, but not PGD2, inhibits the action of high concentrations of PGI2, both when added simultaneously with PGI2 and when added 3 min later. In the latter case the slow spontaneous fall in intracellular cyclic AMP Is accelerated by PGEj but not by PCD2. PGF2, at concentrations up to 100 μM neither stimulated the cyclase by itself, nor did it Inhibit the effects of PGI2, PCE, or PCD2. PCF2α which did cause a small increase in cyclic AMP, inhibited PGD2 strongly, PGE1 not at all, and PCI2 slightly at high concentrations. N0164, an inhibitor of aggregation induced by bls-enoic prostaglandins, inhibited cyclase stimulation by PGD2 but not by PGE1, PGE2, PGD1, or PGI2, though it reduced PGI2-induced inhibition of platelet aggregation. Preaddition of PGE1, but not of PG2, or PGD2, at submaximal concentrations, inhibited subsequent response to high dose PGI2. The results suggest chat PGE1 and PCD2 probably act on the same enzyme, but through a different receptor. PGE1 acts as a partial agonist for the receptor for PCI2, but In addition causes a tachyphylaxis not seen with PCI2, or with, PGD2.

scholarly journals Mechanism of 3-phenylpyruvate-induced insulin release. Secretory, ionic and oxidative aspects

1983 ◽  
Vol 210 (3) ◽  
pp. 913-919 ◽  
Author(s):  
A Sener ◽  
M Welsh ◽  
P Lebrun ◽  
P Garcia-Morales ◽  
M Saceda ◽  
...  
Keyword(s):  
Amino Acid ◽  
Cyclic Amp ◽  
Insulin Release ◽  
Inhibitory Effect ◽  
Secretory Response ◽  
Acid Transport ◽  
O2 Uptake ◽  
Net Uptake ◽  
High Concentrations ◽  
Stimulation Of

1. 3-Phenylpyruvate caused a dose-related stimulation of insulin release from rat pancreatic islets deprived of exogenous nutrient or incubated in the presence of 5.6 or 8.3 mM-D-glucose. 2. 3-Phenylpyruvate inhibited insulin release evoked by high concentrations of D-glucose (16.7 or 27.8 mM) or 4-methyl-2-oxopentanoate (10.0 mM). This inhibitory effect appeared to be attributable to impairment of 2-oxo-acid transport into the mitochondria, with resulting inhibition of D-glucose, pyruvate or 4-methyl-2-oxopentanoate oxidation. 3. 3-Phenylpyruvate failed to affect the oxidation of, and secretory response to, L-leucine, and did not augment insulin release evoked by a non-metabolized analogue of the latter amino acid. 4. L-Glutamine augmented 3-phenylpyruvate-induced insulin release. The release of insulin evoked by the combination of 3-phenylpyruvate and L-glutamine represented a sustained phenomenon, abolished in the absence of extracellular Ca2+ or the presence of menadione and potentiated by theophylline. 5. Whether in the presence or in the absence of L-glutamine, the secretory response to 3-phenylpyruvate coincided with an increase in O2 uptake, a decrease in K+ conductance, a stimulation of both Ca2+ inflow and 45Ca2+ net uptake and an increase in cyclic AMP content. 6. It is concluded that the release of insulin induced by 3-phenylpyruvate displays features classically encountered when the B-cell is stimulated by nutrient secretagogues, and is indeed attributable to an increase in nutrient catabolism.

scholarly journals Specific Inhibition of ADP-Induced Platelet Responses by 2-n-Amylthio Amp

1977 ◽  
Author(s):  
D. E. Maclntyre ◽  
J. L. Gordon ◽  
A. H. Drummond ◽  
M. Steer ◽  
E. W. Salzman
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Potent Inhibitor ◽  
Shape Change ◽  
Inhibitory Effect ◽  
Specific Inhibition ◽  
Synthetic Analogues ◽  
Competitive Antagonist

“Primary” aggregation responses to ADP are blocked by 2-n-amylthio AMP (nAmSAMP)*, apparently competitively (Ki ≃ 10 μM). Shape change is inhibited by higher concentrations (> 0.1 mM). nAmSAMP has a modest inhibitory effect on platelet responses to ionophore Lilly A23187 and a greater effect on responses to collagen and blocks secretion and secondary aggregation induced by ADP, adrenaline, arachidonic acid, PGG2, and synthetic analogues of PGE2 and PGH2-nAmSAMP is a much less potent inhibitor than adenosine against all stimulants apart from ADP and is qualitatively unlike adenosine in the following respects:1. primary aggregation responses to the above agents (except ADP) and to serotonin and vasopressin are unaffected;2. inhibition is not increased by preincubation;3. inhibition is not decreased by an inhibitor of adenylate cyclase, SQ22536 (9-[tetrahydro-2-furyl]-adenine);4. basal levels of platelet cyclic AMP are unaffected. We conclude that, unlike adenosine, nAmSAMP does not inhibit platelet responses by stimulating adenylate cyclase. nAmSAMP appears to be a “specific” competitive antagonist of ADP and should therefore be useful in clarifying the role of ADP in platelet reactions.

In Vitro Effects of Ethanol on Rabbit Platelet Aggregation, Secretion of Granule Contents, and Cyclic AMP Levels in the Presence of Prostacyclin

1989 ◽  
Vol 61 (02) ◽  
pp. 254-258 ◽  
Author(s):  
Margaret L Rand ◽  
Peter L Gross ◽  
Donna M Jakowec ◽  
Marian A Packham ◽  
J Fraser Mustard
Keyword(s):  
Cyclic Amp ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Inhibitory Effects ◽  
Low Concentrations ◽  
Rabbit Platelets ◽  
High Concentrations ◽  
In Vitro Effects ◽  
Aggregation Of Platelets

SummaryEthanol, at physiologically tolerable concentrations, inhibits platelet responses to low concentrations of collagen or thrombin, but does not inhibit responses of washed rabbit platelets stimulated with high concentrations of ADP, collagen, or thrombin. However, when platelet responses to high concentrations of collagen or thrombin had been partially inhibited by prostacyclin (PGI2), ethanol had additional inhibitory effects on aggregation and secretion. These effects were also observed with aspirin- treated platelets stimulated with thrombin. Ethanol had no further inhibitory effect on aggregation of platelets stimulated with ADP, or the combination of ADP and epinephrine. Thus, the inhibitory effects of ethanol on platelet responses in the presence of PGI2 were very similar to its inhibitory effects in the absence of PGI2, when platelets were stimulated with lower concentrations of collagen or thrombin. Ethanol did not appear to exert its inhibitory effects by increasing cyclic AMP above basal levels and the additional inhibitory effects of ethanol in the presence of PGI2 did not appear to be brought about by further increases in platelet cyclic AMP levels.

scholarly journals Interactions between adenylate cyclase and the yeast GTPase-activating protein IRA1.

1991 ◽  
Vol 11 (9) ◽  
pp. 4591-4598 ◽  
Author(s):  
M R Mitts ◽  
J Bradshaw-Rouse ◽  
W Heideman
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Adenylate Cyclase System ◽  
Gtpase Activating Protein ◽  
Yeast Saccharomyces Cerevisiae ◽  
Strong Candidate ◽  
Sepharose 4B ◽  
Stimulation Of ◽  
Cyclic Amp Synthesis

The adenylate cyclase system of the yeast Saccharomyces cerevisiae contains many proteins, including the CYR1 polypeptide, which is responsible for catalyzing the formation of cyclic AMP from ATP, RAS1 and RAS2 polypeptides, which mediate stimulation of cyclic AMP synthesis by guanine nucleotides, and the yeast GTPase-activating protein analog IRA1. We have previously reported that adenylate cyclase is only peripherally bound to the yeast membrane. We have concluded that IRA1 is a strong candidate for a protein involved in anchoring adenylate cyclase to the membrane. We base this conclusion on the following criteria: (i) a disruption of the IRA1 gene produced a mutant with very low membrane-associated levels of adenylate cyclase activity, (ii) membranes made from these mutants were incapable of binding adenylate cyclase in vitro, (iii) IRA1 antibodies inhibit binding of adenylate cyclase to the membrane, and (iv) IRA1 and adenylate cyclase comigrate on Sepharose 4B.

scholarly journals Stimulation of Cyclic AMP Formation by Pituitary Adenylate Cyclase-Activating Polypeptide Is Attenuated by Glutamate in Rat Brain Slices

1995 ◽  
Vol 67 (4) ◽  
pp. 399-402
Author(s):  
Kaoru Kondo ◽  
Hitoshi Hashimoto ◽  
Kazuko Sakata ◽  
Hiroshi Saga ◽  
Jun-ichi Kitanaka ◽  
...  
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Rat Brain ◽  
Brain Slices ◽  
Pituitary Adenylate Cyclase ◽  
Stimulation Of
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