scholarly journals Ca2+-independent fusion of synaptic vesicles with phospholipase A2-treated presynaptic membranes in vitro

1996 ◽  
Vol 318 (3) ◽  
pp. 981-987 ◽  
Author(s):  
Hideaki NISHIO ◽  
Tadayoshi TAKEUCHI ◽  
Fumiaki HATA ◽  
Osamu YAGASAKI
Keyword(s):  
Arachidonic Acid ◽  
Phospholipase A2 ◽  
Rat Brain ◽  
Synaptic Vesicles ◽  
Membrane Phospholipids ◽  
Ach Release ◽  
Fusogenic Activity ◽  
Brain Synaptosomes ◽  
Membrane Pretreatment

To clarify the mechanism of exocytosis in neurotransmitter release, the fusion of synaptic vesicles with presynaptic membranes prepared from rat brain synaptosomes and concomitant acetylcholine (ACh) release induced by fusion of them were studied in vitro. Fusion of the synaptic vesicles with presynaptic membranes was measured by a fluorescence-dequenching assay with octadecyl rhodamine B. Synaptic vesicles fused with presynaptic membranes which had been pretreated with porcine phospholipase A2 (PLA2) in the presence of 20 µM Ca2+ and released ACh, whereas synaptic vesicles did not interact with non-pretreated membranes. The fusion followed by ACh release depended (i) on the activity of PLA2 during the membrane pretreatment, (ii) on the amount of pretreated membrane and (iii) on the duration of the pretreatment. The presence of Ca2+ ions during the pretreatment was essential for inducing a fusogenic activity of the membranes, but Ca2+ ions were not required for the fusion itself because the fusion experiment was carried out in the presence of 5 mM EGTA without added Ca2+. The presence of quinacrine, an antagonist of PLA2, during the membrane pretreatment inhibited their fusogenic activity, suggesting the importance of activation of PLA2. Presence of albumin during the pretreatment, which is an adsorbent of free fatty acids, also inhibited the fusogenic activity. Arachidonic acid, when added during the pretreatment, potentiated the fusogenic activity of the membrane. These findings suggest that the conformational change in the presynaptic membrane phospholipids induced by PLA2 and the presence of arachidonic acid produced by PLA2 are important in the process of fusion of synaptic vesicles with the presynaptic membranes of rat brain, and that the fusion process itself is independent of Ca2+.

scholarly journals Ca2+-independent fusion of secretory granules with phospholipase A2-treated plasma membranes in vitro

1995 ◽  
Vol 307 (2) ◽  
pp. 563-569 ◽  
Author(s):  
T Nagao ◽  
T Kubo ◽  
R Fujimoto ◽  
H Nishio ◽  
T Takeuchi ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Linoleic Acid ◽  
Phospholipase A2 ◽  
Plasma Membranes ◽  
Secretory Granules ◽  
Fusion Process ◽  
Amylase Release ◽  
Fusogenic Activity ◽  
Rat Parotid

The fusion of secretory granules with plasma membranes prepared from rat parotid gland was studied in vitro to clarify the mechanism of exocytosis. Fusion of the granules with plasma membranes was measured by a fluorescence-dequenching assay with octadecyl rhodamine B, and release of amylase was also measured to confirm the fusion as a final step of the secretory process. Plasma membranes that had been pretreated with porcine phospholipase A2 (PLA2) in the presence of 20 microM Ca2+ fused with the granules within 30 s, and induced amylase release by reacting with the membranes of granules, whereas without this pretreatment they had no significant effect. The fusion process accompanied by amylase release was induced in the presence of 10 mM EGTA, and therefore was apparently Ca(2+)-independent. On the other hand, the presence of EGTA or 100 microM quinacrine, an inhibitor of PLA2, during treatment of plasma membranes with PLA2 inhibited their fusogenic activity, suggesting the importance of activation of PLA2. Arachidonic acid and linoleic acid were released from the plasma membranes during the PLA2 treatment. The presence of albumin, an adsorbent of fatty acids, during the treatment also inhibited the activity. Pretreatment of the membranes with arachidonic acid or linoleic acid did not have any effect, but the presence of exogenously added arachidonic acid during PLA2 treatment enhanced the membrane-fusion-inducing effect of PLA2. Pretreatment of the membranes with lysophosphatidylcholine induced fusogenic activity. These findings suggest that the conformational change in the plasma-membrane phospholipids induced by PLA2 and the presence of arachidonic acid or linoleic acid produced by PLA2 are important in the process of fusion of secretory granules with the plasma membranes of rat parotid acinar cells and that the fusion process itself is independent of Ca2+.

Effects of Ethanol on Pathways of Platelet Aggregation In Vitro

1988 ◽  
Vol 59 (03) ◽  
pp. 383-387 ◽  
Author(s):  
Margaret L Rand ◽  
Marian A Packham ◽  
Raelene L Kinlough-Rathbone ◽  
J Fraser Mustard
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Secondary Phase ◽  
Primary Phase ◽  
Rabbit Platelet ◽  
Membrane Phospholipids ◽  
Rabbit Platelets ◽  
Induced Aggregation

SummaryEthanol, at physiologically tolerable concentrations, did not affect the primary phase of ADP-induced aggregation of human or rabbit platelets, which is not associated with the secretion of granule contents. Potentiation by epinephrine of the primary phase of ADP-induced aggregation of rabbit platelets was also not inhibited by ethanol. However, ethanol did inhibit the secondary phase of ADP-induced aggregation which occurs with human platelets in citrated platelet-rich plasma and is dependent on the formation of thromboxane A2. Inhibition by ethanol of thromboxane production by stimulated platelets is likely due to inhibition of the mobilization of arachidonic acid from membrane phospholipids, as ethanol had little or no effect on aggregation and secretion induced by arachidonic acid or the thromboxane mimetic U46619. Rabbit platelet aggregation and secretion in response to low concentrations of collagen, thrombin, or PAF were inhibited by ethanol. Inhibition of the effects of thrombin and PAF was also observed with aspirin-treated platelets. Thus, in addition to inhibiting the mobilization of arachidonate for thromboxane formation that occurs with most agonists, ethanol can also inhibit aggregation and secretion through other effects on platelet responses.

Phospholipase A2-Induced Platelet Aggregation, Release and Lysis.

1979 ◽  
Author(s):  
D. Heinrich ◽  
S. Beckmann
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Phospholipase A2 ◽  
Platelet Membrane ◽  
Membrane Phospholipids ◽  
Specific Antibodies ◽  
High Concentrations

Activation of washed platelets by exogenous phospholipase A2 (PIA2) purified from crotalus terrificus terrificus venom was studied. Platelets were labeled with 14C-serotonin and 51chromium and resuspended in Tyrode/albumin (TA). With 1-5 μg/ml (final conc.) of crotalus PIA2 no direct platelet alterations were observed. These platelets, however, were refractory to collagen - but not to thrombin or HLA-specific antibodies.10-50 μg/ml crotalus PIA2 rapidly induced platelet aggregation and release 100 μg/ml crotalus PIA2 induced platelet lysis.PIA2-induced platelet alterations were inhibited by EDTA, PGE1, ASS and apyrase. Crotapotin, an acid peptid isolated from crotalus venom, forms complexes with crotalus PIA2 and specifically inhibits PIA2-induced platelet alterations.Conclusion: PIA2-induced platelet alterations are due to liberation of arachidonic acid from phospholipids of the platelet membrane inducing prostaglandin and thromboxane synthesis. With high concentrations of PIA2 breakdown of membrane phospholipids will lead to platelet lysis.

scholarly journals Plasma from uninephrectomized rats stimulates phospholipid methylation and arachidonic acid release in renal-cortical slices

1989 ◽  
Vol 260 (2) ◽  
pp. 365-369 ◽  
Author(s):  
H Banfić ◽  
Z Gatalica
Keyword(s):  
Arachidonic Acid ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Phospholipase A2 ◽  
Arachidonic Acid Release ◽  
Kinase C ◽  
Graded Response ◽  
Acid Release ◽  
Cortical Slices

Phospholipid methylation and arachidonic acid release in renal-cortical slices was investigated in vitro after addition of plasma from uninephrectomized or sham-operated rats. Plasma from uninephrectomized rats (‘uni-plasma’) stimulated phospholipid methylation when obtained within the first 3 h after uninephrectomy. With different amounts of added plasma a graded response in phospholipid methylation was obtained. Addition of 50 nM-12-O-tetradecanoylphorbol 13-acetate for 10 min to intact slices also stimulated phospholipid methylation, whereas incubation of slices before addition of ‘uni-plasma’ with 100 microM-1-(5-isoquinolinylsulphonyl)-2-methylpiperazine prevented it, suggesting that protein kinase C stimulates phospholipid methylation in renal-cortical slices. Plasma from uninephrectomized rats also stimulates [3H]arachidonic acid release from phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) via activation of phospholipase A2. Two mechanisms of phospholipase A2 activation are proposed: first, in which it is activated by protein kinase C and releases 3H radioactivity from PtdCho, and second, in which phospholipase A2 is stimulated by Ca2+ ions and releases 3H radioactivity from PtdEtn.

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