Specific binding sites for prostaglandin D2 on human platelets

1979 ◽  
Vol 90 (1) ◽  
pp. 291-296 ◽  
Author(s):  
Adelaide M. Siegl ◽  
J.Bryan Smith ◽  
Melvin J. Silver
Keyword(s):  
Binding Sites ◽  
Specific Binding ◽  
Human Platelets ◽  
Prostaglandin D2 ◽  
Specific Binding Sites

EFFECT OF Ca2+ and Mg2+ ON PLATELET ACTIVATING FACTOR (PAF) INDUCED AGGREGATION AND SPECIFIC BINDING TO HUMAN PLATELETS

1987 ◽  
Author(s):  
C M Chesney ◽  
D D Pifer
Keyword(s):  
Platelet Aggregation ◽  
Calcium Channel ◽  
Binding Sites ◽  
Competitive Inhibition ◽  
Specific Binding ◽  
Human Platelets ◽  
High Affinity ◽  
Specific Binding Sites ◽  
Significant Difference ◽  
Induced Aggregation

Gel filtered human platelets (GFP) collected in Tyrode's buffer containing 0.5 mM Ca+2, ImM Mg+2, and 0.35% albumin exhibit high affinity binding of 3H-PAF with a Kd of 0.109 α 0.029 nM (mean α SD; n=13) and 267 α 70 sites per platelet. When fibrinogen (1.67 mg/ml final concentration) is added to these GFP preparations biphasic aggregation is observed with PAF (4 nM). Normal aggregation is also observed with other platelet agonists including ADP, epinephrine, collagen, arachidonic acid, A23187 and thrombin. If GFP is prepared without added Ca+2 or Mg+2 in the presence of 3mM EDTA, platelets do not aggregate in response to PAF. However the number of specific binding sites remains unchanged (387 per platelet) with some decrease in affinity of binding (Kd = 0.2l4nM). In the presence of ImM Mg+2 there is no significant difference in binding kinetics over a range of Ca+2 concentrations (0-2mM). On the other hand the calcium channel blocker verapamil (5-10uM) exhibits competitive inhibition of 3H-PAF as analyzed by Lineweaver-Burk plots. Specific binding of 3H-PAF to GFP in the presence of ImM Mg+2 and ImM EGTA shows Kd of 0.l66nM but with increase in specific binding sites to 665. Despite increase in number of sites and no change in binding affinity, GFP under these conditions does not exhibit platelet aggregation with PAF in doses up to 80 nM.From these data it appears that external Ca+2 is not necessary for specific binding of 3H-PAF to its high affinity receptor. However, calcium does appear to be necessary for second wave aggregation with PAF. While Mg+2 appears to enhance 3H-PAF binding to platelets Mg+2 cannot substitute for Ca+2 in PAF induced platelet aggregation. Although verapamil appears to competitively inhibit binding of PAF to GFP it is not clear whether the inhibition is due to competition at or near the actual PAF receptor or at a site involving the calcium channel.

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.

Arachidonate Transfer Between Platelets and Lipoproteins

1992 ◽  
Vol 68 (06) ◽  
pp. 719-726 ◽  
Author(s):  
Ingrid I Surya ◽  
Gertie Gorter ◽  
Jan Willem N Akkerman
Keyword(s):  
Binding Sites ◽  
Specific Binding ◽  
Human Platelets ◽  
Temperature Sensitive ◽  
High Concentration ◽  
Prolonged Incubation ◽  
Specific Binding Sites ◽  
Lipid Exchange ◽  
Exchange Processes ◽  
Platelet Functions

SummaryAlthough platelets have specific bindingsites for LDL and HDL, it is doubtful whether lipoproteins modulate platelet functions via receptor-mediated processes. We investigated platelet-lipoprotein interaction during prolonged incubation with concentrations of LDL and HDL that saturate the bindingsites within a few minutes. When [3H]arachidonate-labeled human platelets were incubated for 4 h with lipoproteins, part of the 3H-radioactivity transferred to LDL and to a lesser extent to HDL. The transfer was temperature-sensitive, unaffected by modification of lysine in LDL or indomethacin treatment of the platelets, and almost irreversible. [3H]arachidonate transfer to lipoproteins could be mimicked by incubating platelets with a high concentration of fatty acid free albumin. This showed, that the loss of 3H-radioactivity reflected a decrease in endogenous arachidonate, leading to impaired aggregation, secretion and thromboxane B2 formation in platelets after stimulation with thrombin but not with arachidonate. Thus, the decrease in platelet functions seen after long incubation with HDL is caused by depletion of platelet arachidonate. Despite an even stronger arachidonate depletion by LDL, this lipoprotein initiated arachidonate metabolism and secretion independent of specific binding sites for LDL on the platelet. Surprisingly, the major part of the secretion was preserved when the formation of prostaglandin endoperoxides/ thromboxane A2 was inhibited with indomethacin. These findings argue against a role for LDL and HDL receptors in the modulation of platelet functions and are more in favor of lipid exchange processes between platelets and lipoproteins.

scholarly journals Specific Binding of Rubidium in Chlorella

1962 ◽  
Vol 45 (5) ◽  
pp. 959-977 ◽  
Author(s):  
Dan Cohen
Keyword(s):  
Active Transport ◽  
Binding Sites ◽  
Specific Binding ◽  
High Concentration ◽  
External Concentration ◽  
Specific Binding Sites ◽  
Dense Suspension ◽  
Concentration Of Ions ◽  
The Individual ◽  
A Site

Specific binding sites for potassium, which may be components of the carriers for active transport for K in Chlorella, were characterized by their capacity to bind rubidium. A dense suspension was allowed to take up Rb86 from a low concentration of Rb86 and a high concentration of ions which saturate non-specific sites. The amount bound was derived from the increase in the external concentration of Rb86 following addition of excess potassium. The sites were heterogeneous. The average affinity of Rb and various other ions for the sites was determined by plotting the degree of displacement of Rb86 against log molar concentration of the individual ions. Interpolation gave the concentration for 50 per cent displacement of Rb, which is inversely related to affinity. The order of affinity was not changed when the cells were frozen, or boiled either in water or in 70 per cent ethanol. The affinity is maximal for ions with a crystalline radius of 1.3 to 1.5 A and a high polarizability, and is not related to the hydrated radius or valency. It is suggested that binding groups in a site are rigidly arranged, the irregular space between them being 2.6 to 3.0 A across, so that affinity is high for ions of this diameter and high polarizability.

Studies of the uptake of macromolecules by cells. I. Uptake of proteins by cells of the Ehrlich–Lettré ascites carcinoma

1968 ◽  
Vol 46 (12) ◽  
pp. 1443-1450 ◽  
Author(s):  
Y. C. Choi ◽  
E. R. M. Kay
Keyword(s):  
Nucleic Acid ◽  
Cell Membrane ◽  
Binding Sites ◽  
Specific Binding ◽  
Protein Uptake ◽  
Specific Binding Sites ◽  
Model Protein ◽  
Uptake Process ◽  
Kinetics Of ◽  
Protein Treatment

The uptake of protein by cells of the Ehrlich–Lettré ascites carcinoma was characterized kinetically by using hemoglobin as a model protein. An attempt was made to show that the process is not an artefact due to nonspecific adsorption of protein to the cell membrane. The kinetics of the uptake process suggested that an interaction exists between the exogenous protein and specific binding sites on the membrane. Acetylation of hemoglobin enhanced the rate of uptake of this protein. Treatment of cells with neuraminidase, phospholipase A, and Pronase resulted in an inhibition of protein uptake. The experimental evidence for the uptake of hemoglobin was supported by evidence that L-serine-U-14C-labelled hemoglobin is transported into the cytoplasm and utilized subsequently, resulting in labelling of the nucleic acid nucleotides.

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