scholarly journals The secretory pathway of bovine platelets

Blood ◽  
1987 ◽  
Vol 69 (3) ◽  
pp. 878-885 ◽  
Author(s):  
JG White
Keyword(s):  
Plasma Membrane ◽  
Secretory Pathway ◽  
Human Platelet ◽  
Surface Membrane ◽  
Surrounding Medium ◽  
Human Platelets ◽  
Resting Cells ◽  
Granule Secretion ◽  
New Perspective ◽  
Platelet Secretion

Abstract Human platelets contain tortuous channels in their cytoplasm, the surface-connected or open canalicular system (OCS), that communicate directly with the surrounding medium through openings on the surface membrane. Some workers have suggested that the OCS serves as the egress route for products secreted during the release reaction. Others have proposed alternate secretory pathways. Since bovine platelets lack the OCS found in human cells, the present study has examined the secretory mechanism of these cells to see whether it can shed light on the mystery of human platelet secretion. Bovine platelet granules, in contrast to human granules, are located more peripherally in resting cells (often in contact with the plasma membrane), most do not move centrally following thrombin stimulation as do human platelet granules, and many fuse directly with the external plasma membrane without any intermediate channel. The lack of peripheral location of human granules, their central rather than peripheral movement during secretion, and the presence of extensive channels are all consistent with the larger importance of the secretory channel to human platelets. Thus, though studies of bovine secretion do show that platelets can secrete their granules by direct fusion of granule and surface membranes, other differences from human platelets emphasize that this pathway, although important to bovine platelet secretion, is less important in human platelets. Studies of bovine platelets also show that the OCS is more dynamic than might have been considered from human studies and can form rapidly in response to stimulation. Such newly formed channels are used as a conduit for secretion of granule contents. The finding emphasizes the importance of channels for granule secretion in platelets generally and puts a new perspective on the ability of these cells to form channels rapidly in response to stimulation.

scholarly journals The secretory pathway of bovine platelets

Blood ◽  
1987 ◽  
Vol 69 (3) ◽  
pp. 878-885 ◽  
Author(s):  
JG White
Keyword(s):  
Plasma Membrane ◽  
Secretory Pathway ◽  
Human Platelet ◽  
Surface Membrane ◽  
Surrounding Medium ◽  
Human Platelets ◽  
Resting Cells ◽  
Granule Secretion ◽  
New Perspective ◽  
Platelet Secretion

Human platelets contain tortuous channels in their cytoplasm, the surface-connected or open canalicular system (OCS), that communicate directly with the surrounding medium through openings on the surface membrane. Some workers have suggested that the OCS serves as the egress route for products secreted during the release reaction. Others have proposed alternate secretory pathways. Since bovine platelets lack the OCS found in human cells, the present study has examined the secretory mechanism of these cells to see whether it can shed light on the mystery of human platelet secretion. Bovine platelet granules, in contrast to human granules, are located more peripherally in resting cells (often in contact with the plasma membrane), most do not move centrally following thrombin stimulation as do human platelet granules, and many fuse directly with the external plasma membrane without any intermediate channel. The lack of peripheral location of human granules, their central rather than peripheral movement during secretion, and the presence of extensive channels are all consistent with the larger importance of the secretory channel to human platelets. Thus, though studies of bovine secretion do show that platelets can secrete their granules by direct fusion of granule and surface membranes, other differences from human platelets emphasize that this pathway, although important to bovine platelet secretion, is less important in human platelets. Studies of bovine platelets also show that the OCS is more dynamic than might have been considered from human studies and can form rapidly in response to stimulation. Such newly formed channels are used as a conduit for secretion of granule contents. The finding emphasizes the importance of channels for granule secretion in platelets generally and puts a new perspective on the ability of these cells to form channels rapidly in response to stimulation.

Differential Ability of Agonists to Express Distinct Pools of Fibrinogen (Gpllb/llla) Receptors which Can Mediate the Aggregation of Human Platelets

1989 ◽  
Vol 62 (03) ◽  
pp. 955-961 ◽  
Author(s):  
Ian S Watts ◽  
Rebecca J Keery ◽  
Philip Lumley
Keyword(s):  
Platelet Aggregation ◽  
Human Platelet ◽  
Surface Membrane ◽  
Blood Platelet ◽  
Human Platelets ◽  
Membrane Glycoprotein ◽  
Platelet Surface ◽  
Human Platelet Aggregation ◽  
Differential Ability ◽  
Blood Platelet Aggregation

SummaryWe have investigated the effect of two procedures that modify human platelet surface membrane glycoprotein (Gp) IIb and IIIa complexes upon whole blood platelet aggregation to a range of agonists. (A) Irreversible disruption of complexes by temporary (30 min) Ca2+-deprivation with EGTA at 37° C. (B) Binding of a monoclonal antibody M148 to the complex. EGTA exposure abolished aggregation to ADP, adrenaline and PAF. In contrast, full aggregation curves to collagen and U-46619 could still be established. EGTA exposure reduced M148 binding to platelets by 80%. Excess M148 abolished aggregation to ADP, PAF, collagen and U-46619. However, upon removal of unbound antibody from platelets full aggregation curves to collagen and U-46619 but not to ADP and PAF could be re-established. Thus human platelet aggregation to ADP, PAF and adrenaline appears absolutely dependent upon surface membrane GpIIb/IIIa complexes. In contrast, collagen and U-46619 cause expression of an additional distinct pool of Gp complexes inaccessible to EGTA and M148 in unstimulated platelets which is intimately involved in aggregation to these agonists.

Platelet Secretion Induced by Calcium Ionophores: Effect of Anti-Inflammatory Drugs

1975 ◽  
Author(s):  
E. H. Mürer ◽  
K. Davenport ◽  
H. J. Day
Keyword(s):  
Incubation Time ◽  
Surrounding Medium ◽  
Human Platelets ◽  
Serotonin Release ◽  
Time Dependent ◽  
Metabolic Parameters ◽  
Platelet Serotonin ◽  
Inflammatory Drugs ◽  
Anti Inflammatory ◽  
Platelet Secretion

Washed human platelets prelabeled with 3 H-serotonin and 14 C-adenine were incubated at 37° C with ionophores A23187 and X537A. 0.1 μM A23187 released the serotonin store of preincubated platelets after 1 min at 37° C, but was less effective when added in the cold. An increase in incubation time at 37° C did not result in increased release. Platelets preincubated with indomethacin showed reduction of up to 85% in released serotonin, while the metabolic parameters 14 C-ATP and 14 C-IMP were not significantly altered. The platelets from some donors did not show reduced release after treatment with indomethacin. This may indicate a variation in sensitivity to the release inducer similar to that described for Sr++-induced release (Biochim. Biophys. Acta 53-59, 362, 1974), or to the effect of indomethacin. 1 μM X537A caused a time-dependent serotonin release which increased from 2% at 1 min to 58% at 10 min incubation at 37° C. There was little change in 14 C-ATP following release and none in intra- or extracellular 14 C-IMP. 10 μM X537A caused release of 75-80% of the platelet serotonin after 1 min incubation. Longer incubation resulted in 14 C-IMP accumulation and leakage of 14 C-IMP to the surrounding medium. The results do not support the view that X537A and A23187 cause release from platelets by different mechanisms.(Supported by grant HL 14217 from NHLI. A23187 was a gift from Dr. R. L. Hamill, Eli Lilly and Co., Indianapolis, Ind., and X537A from Drs. Zane Gaut and W. E. Scott, Hoffmann-LaRoche, Inc., Nutley, N. J.)

Epinephrine correction of impaired platelet thromboxane receptor signaling

2000 ◽  
Vol 279 (6) ◽  
pp. C1760-C1771 ◽  
Author(s):  
Patricia C. Dunlop ◽  
Linda A. Leis ◽  
Gerhard J. Johnson
Keyword(s):  
G Protein ◽  
Human Platelet ◽  
Human Platelets ◽  
Binding Studies ◽  
G Protein Coupling ◽  
Protein Coupling ◽  
Thromboxane Receptor ◽  
Tp Receptor ◽  
Tp Receptors ◽  
Platelet Secretion

This study evaluated the mechanism of epinephrine potentiation of platelet secretion induced by thromboxane A2(TXA2). Dog platelets that do not secrete in response to TXA2alone (TXA2−) were compared with dog platelets that do secrete (TXA2+) and with human platelets. TXA2− platelets had impaired TXA2receptor (TP receptor)-G protein coupling, indicated by 1) impaired stimulated GTPase activity, 2) elevated basal guanosine 5′- O-(3-thiotriphosphate) binding, and 3) elevated Gαqpalmitate turnover that was corrected by preexposure to epinephrine. Kinetic agonist binding studies revealed biphasic dog and human platelet TP receptor association and dissociation. TXA2− and TP receptor-desensitized TXA2+ dog and human platelets had altered ligand binding parameters compared with untreated TXA2+ or human platelets. These parameters were reversed, along with impaired secretion, by epinephrine. Basal phosphorylation of TXA2− platelet TP receptors was elevated 60% and was normalized by epinephrine. Epinephrine potentiates platelet secretion stimulated by TXA2by reducing basal TP receptor phosphorylation and facilitating TP receptor-G protein coupling in TXA2− platelets and, probably, in normal platelets as well.

Role of Caspase in a Subset of Human Platelet Activation Responses

Blood ◽  
1999 ◽  
Vol 93 (12) ◽  
pp. 4222-4231 ◽  
Author(s):  
Anna Shcherbina ◽  
Eileen Remold-O’Donnell
Keyword(s):  
Platelet Activation ◽  
Caspase 3 ◽  
Human Platelet ◽  
Thrombus Formation ◽  
Shape Change ◽  
Vascular Wall ◽  
Human Platelets ◽  
Granule Secretion ◽  
Platelets Function

Abstract Platelets function to protect the integrity of the vascular wall. A subset of platelet activation responses that are especially important for thrombus formation include exposure of phosphatidylserine and release of microparticles, which generate procoagulant surfaces. The resemblance of these platelet activation processes to events occurring in nucleated cells undergoing apoptosis suggests a possible role for caspases, which are major effector enzymes of nucleated cell apoptosis. We demonstrate here the presence of caspase-3 in human platelets and its activation by physiological platelet agonists. Using cell-permeable specific inhibitors, we demonstrate a role for a caspase-3–like protease in the agonist-induced (collagen plus thrombin or Ca2+ ionophore) platelet activation events of phosphatidylserine exposure, microparticle release, and cleavage of moesin, a cytoskeletal-membrane linker protein. The role of caspase-3 in platelet activation is restricted rather than global, because other activation responses,  granule secretion, shape change, and aggregation were unaffected by caspase-3 inhibitors. Experiments with two classes of protease inhibitors show that caspase-3 function is distinct from that of calpain, which is also involved in late platelet activation events. These findings show novel functions of caspase and provide new insights for understanding of platelet activation.

THE SECRETORY PATHWAY IN PLATELETS STUDIED BY CRYO-FIXATION

1987 ◽  
Author(s):  
E morqenstern ◽  
H Patscheke
Keyword(s):  
Osmium Tetroxide ◽  
Secretory Pathway ◽  
Freeze Substitution ◽  
Human Platelets ◽  
Dense Matrix ◽  
Compound Exocytosis ◽  
Ultrathin Sections ◽  
Granule Secretion ◽  
Large Compound ◽  
Electron Dense Matrix

It is widely held, that the constituents packed in the a -granules are released by stimulated platelets via the surface connected system (SCS). By means of the fast-freezing and freeze substitution technique (which allow the investigation of membrane fusion) we found a secretory pathway in platelets (compound exocytosis) without an involvement of the SCS during the release of a-granules. To study the process of a-granule secretion human platelets concentrated in citrated blood plasm were stimulated with thrombin or collagen. 20 - 120 seconds after stimulation the platelets were rapidly frozen with a metal-mirror attachment to the KF 80 cryofixation unit (REICHERT-JUNG). Using plastic spacers droplets of the PRP were slammed against a copper block at 80 K at a rate of 0.2 m/sec. After cryofixation the specimens were transferred (in liquid nitrogen) into a Cs-auto cryosubstitution unit (REICHERT-JUNG). Cryosubstitution was programmed for 48h at 193 K in acetone with 4% osmium tetroxide. The temperature went automatically up to room temperature at a rate of 10 K/h. The specimens were embedded in araldite. The analysis of serial ultrathin sections of platelets in different phases of exocytosis revealed the following. a -granules in apposition showed different stages of swelling and dispersal of their electron dense matrix. Membrane appositions were also found between a -granules. The contraction of a sphere of microfilaments and microtubules during stimulation seemed to support this process. On the other hand this internal contraction prevented most of the a-granules from contacting with the plasmalemma. We observed fusion between swollen -granules in apposition and the plasmalemma and swollen and unswollen a -granules. Thus, large compound granules were formed frequently before fusion of the secretory organelles with the plasmalemma took place. These observations suggested that a -granules in stimulated platelets performed a compound exocytosis after swelling. The process seemed to start with the apposition of a -granule membranes to the plasmalemma. It cannot yet be answered whether the swelling of the granules is due to an osmotically driven influx of water or due to an influx after microfusion.Supported by DFG, Grant Mo 124/2-4

Paxillin Becomes Tyrosine-Phosphorylated and Binds Csk in a GpIIb-IIIa-Dependent Manner Following GPVI-Induced Activation of Murine Platelets.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3889-3889
Author(s):  
Vipul B. Rathore ◽  
Peter J. Newman ◽  
Debra K. Newman
Keyword(s):  
Platelet Activation ◽  
Binding Proteins ◽  
Critical Role ◽  
Human Platelets ◽  
Sh2 Domain ◽  
Intramolecular Interactions ◽  
Resting Cells ◽  
Dependent Manner ◽  
Granule Secretion ◽  
Collagen Receptor

Though Src family kinases (SFKs) play a critical role in collagen-induced platelet activation, little is known about how SFK activity is regulated following exposure of platelets to collagen. In resting cells, SFKs are maintained in an inactive conformation, in part, via intramolecular interactions between their SH2 domain and a C-terminal tyrosine residue whose phosphorylation state is controlled by the C-terminal Src kinase, Csk. Access of Csk to SFKs, in turn, is regulated by recruitment of Csk, via its SH2 domain, to one or more tyrosine-phosphorylated Csk-binding proteins, which include Csk binding protein (Cbp/PAG) itself, paxillin, and its closely-related paxillin family member, Hic-5. Recent studies have shown that human platelets possess only two Csk-binding proteins: Cbp/PAG and Hic-5, and that Hic-5 can become tyrosine-phosphorylated when platelets are stimulated with a variety of platelet agonists, including, thrombin, U46619, and collagen. The purpose of the present investigation was to characterize the complement of Csk-binding proteins in murine platelets and to begin to determine their role in regulating collagen-induced platelet activation. Murine platelets, like human platelets, were found to express Hic-5, and in addition contained two other Csk-binding proteins: paxillin and leupaxin. Of these, both paxillin and Hic-5 became tyrosine phosphorylated, and paxillin was shown to be able to recruit Csk in a time-dependent manner following exposure of murine platelets to collagen and the GPVI/FcRg chain collagen receptor-specific agonist, CRP. These data suggest that the function of Hic-5 in human platelets may be performed by both Hic-5 and paxillin in mice. Finally, both paxillin tyrosine phosphorylation and Csk recruitment were blocked by agents that interfered with either platelet granule secretion or with integrin engagement, consistent with the notion that members of the paxillin family function as integrin-dependent negative feedback regulators of platelet adhesion and spreading.

scholarly journals Further studies of the secretory pathway in thrombin-stimulated human platelets

Blood ◽  
1987 ◽  
Vol 69 (4) ◽  
pp. 1196-1203 ◽  
Author(s):  
JG White ◽  
M Krumwiede
Keyword(s):  
Tannic Acid ◽  
Secretory Pathway ◽  
Surrounding Medium ◽  
Human Platelets ◽  
Secretory Process ◽  
Intense Staining ◽  
Platelet Surface ◽  
Dense Deposits ◽  
Dense Substance ◽  
Secretory Products

Abstract The pathway followed by secretory products stored in platelet alpha granules during the release reaction remains controversial. Tannic acid has been used in the present study as an electron-dense stain to follow the secretory process in thrombin-stimulated platelets. Preliminary experiments demonstrated that tannic acid precipitates fibrinogen, and binds osmium tetroxide to fibrinogen and fibrin strands. Examination of platelets fixed at short intervals after exposure to thrombin and incubated in solutions containing tannic acid revealed electron-dense deposits of osmium not apparent in resting platelets. Granules and lumina of channels making up the open canalicular system (OCS) were unstained in discoid cells. However, exposure to thrombin at concentrations of 1 to 5 U/mL for thirty seconds or more resulted in intense staining of alpha granules by osmium. Some granules communicated directly with dilated channels of the OCS, and several were frequently connected to the same canaliculus. The electron-dense substance in swollen granules and channels appeared to be in the process of extrusion through narrow or dilated openings of the OCS onto the platelet surface. Granule-to-granule fusion and formation of sealed vacuoles of fused granule products unstained by tannic acid-osmium were not observed. The findings support the concept that secretion by stimulated human platelets results from development of direct communications between granules and channels of the OCS and subsequent extrusion of products through channel pores to the surrounding medium.

scholarly journals Further studies of the secretory pathway in thrombin-stimulated human platelets

Blood ◽  
1987 ◽  
Vol 69 (4) ◽  
pp. 1196-1203 ◽  
Author(s):  
JG White ◽  
M Krumwiede
Keyword(s):  
Tannic Acid ◽  
Secretory Pathway ◽  
Surrounding Medium ◽  
Human Platelets ◽  
Secretory Process ◽  
Intense Staining ◽  
Platelet Surface ◽  
Dense Deposits ◽  
Dense Substance ◽  
Secretory Products

The pathway followed by secretory products stored in platelet alpha granules during the release reaction remains controversial. Tannic acid has been used in the present study as an electron-dense stain to follow the secretory process in thrombin-stimulated platelets. Preliminary experiments demonstrated that tannic acid precipitates fibrinogen, and binds osmium tetroxide to fibrinogen and fibrin strands. Examination of platelets fixed at short intervals after exposure to thrombin and incubated in solutions containing tannic acid revealed electron-dense deposits of osmium not apparent in resting platelets. Granules and lumina of channels making up the open canalicular system (OCS) were unstained in discoid cells. However, exposure to thrombin at concentrations of 1 to 5 U/mL for thirty seconds or more resulted in intense staining of alpha granules by osmium. Some granules communicated directly with dilated channels of the OCS, and several were frequently connected to the same canaliculus. The electron-dense substance in swollen granules and channels appeared to be in the process of extrusion through narrow or dilated openings of the OCS onto the platelet surface. Granule-to-granule fusion and formation of sealed vacuoles of fused granule products unstained by tannic acid-osmium were not observed. The findings support the concept that secretion by stimulated human platelets results from development of direct communications between granules and channels of the OCS and subsequent extrusion of products through channel pores to the surrounding medium.

scholarly journals Specific binding sites for inositol 1,3,4,5-tetrakisphosphate are located predominantly in the plasma membranes of human platelets

1994 ◽  
Vol 298 (3) ◽  
pp. 739-742 ◽  
Author(s):  
P J Cullen ◽  
Y Patel ◽  
V V Kakkar ◽  
R F Irvine ◽  
K S Authi
Keyword(s):  
Plasma Membrane ◽  
Binding Sites ◽  
Plasma Membranes ◽  
Human Platelet ◽  
Specific Binding ◽  
Human Platelets ◽  
Intracellular Membranes ◽  
Specific Binding Sites ◽  
Carrier Free ◽  
Membrane Location

In the present study we describe the characterization and localization of Ins(1,3,4,5)P4-binding sites in human platelet membranes. Specific binding sites for Ins(1,3,4,5)P4 have been identified on mixed, plasma and intracellular membranes from neuraminidase-treated platelets using highly purified carrier-free [32P]Ins(1,3,4,5)P4. The displacement of Ins(1,3,4,5)P4 from these sites by Ins(1,4,5)P3 and InsP6 occurs at greater than two orders of magnitude higher concentrations and with Ins(1,3,4,5,6)P5 at about 40-fold higher concentrations than with Ins(1,3,4,5)P4. The membranes were further separated by free-flow electrophoresis into plasma and intracellular membranes. The Ins(1,3,4,5)P4-binding sites separated with plasma membranes, and showed similar affinities and specificities as mixed membranes, whereas Ins(1,4,5)P3-binding sites were predominantly in the intracellular membranes. These results suggest a predominantly plasma membrane location for putative Ins(1,3,4,5)P4 receptors in human platelets.

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