Identification of ecto-PKC on surface of human platelets: role in maintenance of latent fibrinogen receptors

2000 ◽  
Vol 278 (6) ◽  
pp. H2008-H2019 ◽  
Author(s):  
Anna Babinska ◽  
Michael V. Hogan ◽  
Tomasz Sobocki ◽  
Malgorzata B. Sobocka ◽  
Yigal H. Ehrlich ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Calcium Concentration ◽  
Surface Protein ◽  
Human Platelets ◽  
Surface Proteins ◽  
Free Calcium ◽  
Platelet Surface ◽  
Inhibitory Peptides ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration

Human platelets express a protein phosphorylation system on their surface. A specific protein kinase C (PKC) antibody, monoclonal antibody (MAb) 1.9, which binds to the catalytic domain of PKC and inhibits its activity, causes the aggregation of intact platelets while inhibiting the phosphorylation of platelet surface proteins. Photoaffinity labeling with 100 nM 8-azido-[α32P]ATP identified this ecto-PKC as a single surface protein of 43 kDa sensitive to proteolysis by extracellular 0.0005% trypsin. Inhibition of the binding of 8-azido-[α32P]ATP to the 43-kDa surface protein by MAb 1.9 identified this site as the active domain of ecto-PKC. Covalent binding of the azido-ATP molecule to the 43-kDa surface protein inhibited the phosphorylative activity of the platelet ecto-PKC. Furthermore, PKC pseudosubstrate inhibitory peptides directly induced the aggregation of platelets and inhibited azido-ATP binding to the 43-kDa protein. Platelet aggregation induced by MAb 1.9 and by PKC inhibitory peptides required the presence of fibrinogen and resulted in an increase in the level of intracellular free calcium concentration. This increase in intracellular free calcium concentration induced by MAb 1.9 was found to be dependent on the binding of fibrinogen to activated GPIIb/IIIa integrins, suggesting that MAb 1.9 causes Ca2+flux through the fibrinogen receptor complex. We conclude that a decrease in the state of phosphorylation of platelet surface proteins caused by inhibition of ecto-PKC results in membrane rearrangements that can induce the activation of latent fibrinogen receptors, leading to platelet aggregation. Accordingly, the maintenance of a physiological steady state of phosphorylation of proteins on the platelet surface by ecto-PKC activity appears to be one of the homeostatic mechanisms that maintain fibrinogen receptors of circulating platelets in a latent state that cannot bind fibrinogen.

Role of Protein Kinase C in the Anti-Aggregatory Effects of Endothelin-1 on Human Platelets

1995 ◽  
Vol 88 (3) ◽  
pp. 277-283 ◽  
Author(s):  
R. M. Touyz ◽  
E. L. Schiffrin
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Calcium Concentration ◽  
Human Platelets ◽  
Intracellular Free Calcium ◽  
Free Calcium ◽  
Endothelin 1 ◽  
Kinase C ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration

1. Endothelin-1 has anti-aggregatory properties, but the mechanism underlying this inhibitory action is unknown. This in vitro study investigates effects of endothelin-1 on thrombin-stimulated aggregation and intracellular free calcium concentration in human platelets and assesses the role of protein kinase C in the interactions between endothelin-1 and thrombin. Aggregation was measured turbidometrically and the intracellular free calcium concentration was determined with the fluorescent indicator fura 2-acetoxymethyl ester. 2. Endothelin-1 at concentrations from 10−11 to 10−6 mol/l had no effect on platelet aggregation or intracellular free calcium concentration but inhibited in a dose-dependent manner aggregation induced by 0.05 unit/ml thrombin (pD2 for inhibition by endothelin = 8.1 ± 0.12). 3. Endothelin-1 at 10−9 mol/l significantly decreased (P<0.01) thrombin-stimulated aggregation from 81.4 ± 1.5% (in the absence of endothelin-1) to 53.5 ± 1.1% (in the presence of endothelin) and thrombin-stimulated intracellular free calcium concentration from 179 ± 1.7 nmol/l to 140 ± 1.8 nmol/l. 4. Preincubation of platelets with 10−7 mol/l staurosporine (protein kinase C inhibitor), calphostin C (highly selective protein kinase C inhibitor) or 5-(N,N-hexamethylene) amiloride (highly selective Na+-H+ exchange blocker) significantly inhibited (P < 0.01) thrombin-stimulated platelet responses and suppressed the inhibitory effect of endothelin-1 on thrombin-induced aggregation and intracellular free calcium concentration. 5. In conclusion, endothelin-1 decreases the aggregatory response of human platelets to thrombin by mechanisms that probably involve protein kinase C and Na+-H+ linked pathways.

Activation of human platelets by protein kinase C antibody: role for surface phosphorylation in homeostasis

1996 ◽  
Vol 271 (5) ◽  
pp. H2134-H2144 ◽  
Author(s):  
A. Babinska ◽  
Y. H. Ehrlich ◽  
E. Kornecki
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Surface Protein ◽  
Human Platelets ◽  
Surface Proteins ◽  
Protein Kinase Activity ◽  
Platelet Surface ◽  
Inhibitory Peptides ◽  
Kinase C ◽  
Fibrinogen Binding

A monoclonal antibody that inhibits protein kinase C (PKC) activity, as well as PKC pseudosubstrate inhibitory peptides, was found to cause aggregation of human platelets followed by granular secretion. Binding of this antibody to the platelet surface was demonstrated directly by flow cytometry and immunofluorescence microscopy. Assays of ecto-protein kinase activity revealed that this antibody inhibits the phosphorylation of five proteins on the platelet surface. The platelet aggregation induced by extracellular PKC inhibitors could be blocked by the addition of the membrane-impermeable phosphatase inhibitor, microcystin. Thus the inhibition of surface protein phosphorylation together with continuous dephosphorylation, namely, a decrease in the phosphorylation state of surface proteins, causes the activation of platelets. The aggregation caused by decreased surface phosphorylation appears to be initiated by the exposure of active fibrinogen-binding sites on the platelet surface, as demonstrated by the formation of fibrinogen-dependent microaggregates, as the first step in this process. We conclude that the phosphorylation of surface proteins by a platelet ecto-protein kinase C protects platelets from spontaneous aggregation and thus can play an important role in homeostatic mechanisms that maintain circulating platelets in a resting state.

P2 purinoceptor localization along rat nephron and evidence suggesting existence of subtypes P2Y1 and P2Y2

1998 ◽  
Vol 274 (6) ◽  
pp. F1006-F1014 ◽  
Author(s):  
Seok Ho Cha ◽  
Takashi Sekine ◽  
Hitoshi Endou
Keyword(s):  
Calcium Concentration ◽  
Free Calcium ◽  
Dependent Manner ◽  
Reactive Blue 2 ◽  
Collecting Tubule ◽  
Single Nephron ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration ◽  
Dose Dependent ◽  
Cortical Collecting Tubule

Effects of extracellular ATP on intracellular free calcium concentration ([Ca2+]i) were examined in rat single nephron segments using the fura 2-AM. ATP (10 μM) induced a significant transient increase in [Ca2+]iin the glomerulus, the early proximal convoluted tubule (S1), the cortical collecting tubule (CCT), and the outer medullary collecting tubule (OMCT). The magnitude of the response was the greatest in the OMCT among four segments. ATP induced an increase in the [Ca2+]iin a dose-dependent manner in S1 and OMCT. In the OMCT, ATP caused a biphasic increase in [Ca2+]iconsisting of an initial rapid rise and a sustained phase. Removal of calcium from the medium resulted in an attenuation of the sustained phase of [Ca2+]iand an ∼30% reduction in the height of the initial [Ca2+]ipeak in response to 10 μM ATP. Effects of ATP, its analogs, and its metabolites were tested in the S1 and OMCT. ATP, 2-methylthio-ATP (2-MeS-ATP), ADP, and UTP increased [Ca2+]idose dependently. AMP and adenosine did not affect [Ca2+]iin the S1 and OMCT. The ATP- or 2-MeS-ATP-induced [Ca2+]iincrease was inhibited by the pretreatment of the S1 and OMCT with suramin or reactive blue 2. Neomycin, a phospholipase C inhibitor, attenuated the ATP-induced [Ca2+]iincrease. To investigate the hormonelike action of ATP in OMCT, a heterologous cross desensitization was performed. The pretreatment of OMCT with ATP inhibited increases in vasopressin-, ANG II-, endothelin-1-, or bradykinin-induced [Ca2+]iincrease. These findings suggest that ATP might affect the above peptidyl agonist-activated calcium mobilizations.

A cross-sectional study of basal platelet intracellular free calcium concentration in normotensive and hypertensive primigravid pregnancies

1990 ◽  
Vol 78 (1) ◽  
pp. 75-80 ◽  
Author(s):  
M. D. Kilby ◽  
F. Broughton Pipkin ◽  
S. Cockbill ◽  
S. Heptinstall ◽  
E. M. Symonds
Keyword(s):  
Calcium Concentration ◽  
Post Partum ◽  
Cross Sectional Study ◽  
Free Calcium ◽  
Sectional Study ◽  
Third Trimester ◽  
Cross Sectional ◽  
The Third ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration

1. The intracellular free calcium concentration ([Ca2+]i) in washed human platelets was measured using the fluorescent indicator, fura-2, in a cross-sectional study of 36 normotensive, primigravid volunteers, 12 in each trimester of pregnancy and a further 12 at 6 weeks post partum. The results were compared with those obtained from 30 normal female volunteers not using oral contraception. 2. The mean basal [Ca2+]i in the platelets of the pregnant women in the first two trimesters (115.6 ± 6.7 and 120.1 ± 5.7 nmol/l, respectively) was not shown to differ significantly from that of normal non-pregnant volunteers (112.3 ± 2.9 nmol/l). However, during the third trimester a significant increase in [Ca2+]i was noted (134.0 ± 4.9 nmol/l; P < 0.05), with a return to normal values in the post-partum period (108.2 ± 6.1 nmol/l). 3. [Ca2+]i was also measured in the platelets of a group of 12 primigravid pregnant women in the third trimester whose pregnancies were complicated by gestational hypertension (pregnancy-induced hypertension and preeclampsia). A significant rise in basal [Ca2+]i was noted in the platelets of primigravidae whose pregnancies were complicated by pre-eclampsia (163.6 ± 8.8 nmol/l) as compared with normotensive, third-trimester primigravidae (P < 0.02). However, no correlation could be demonstrated between [Ca2+]i and systemic blood pressure.

scholarly journals The effect of mitogenic lectins and monoclonal antibodies on intracellular free calcium concentration in human T-lymphocytes

1984 ◽  
Vol 219 (2) ◽  
pp. 661-666 ◽  
Author(s):  
K O'Flynn ◽  
D C Linch ◽  
P E R Tatham
Keyword(s):  
T Cells ◽  
Monoclonal Antibodies ◽  
T Cell ◽  
Calcium Concentration ◽  
Human Lymphocytes ◽  
Maximum Level ◽  
T Cell Response ◽  
Free Calcium ◽  
Intracellular Free Calcium Concentration ◽  
Free Calcium Concentration

The effect of mitogenic lectins and the mitogenic antibody UCHT1 on the cytoplasmic free Ca2+ concentration ([Ca2+]i) in human lymphocytes was investigated by using the fluorescent Ca2+-indicator quin2 . Phytohaemagglutinin, concanavalin A and UCHT1 increased [Ca2+]i in T-cells to a maximum level within 2 min. No T-cell response was seen with poke weed mitogen. None of the mitogens affected non-T-cell [Ca2+]i.

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