scholarly journals Pharmacological Characterization of Inositol 1,4,5-tris Phosphate Receptors in Human Platelet Membranes

2009 ◽  
Vol 2009 ◽  
pp. 1-8 ◽  
Author(s):  
Yogesh Dwivedi ◽  
Ghanshyam N. Pandey
Keyword(s):  
Binding Sites ◽  
Inositol Phosphates ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Signaling System ◽  
Healthy Human ◽  
Pharmacological Characterization ◽  
Human Control ◽  
Platelet Membranes ◽  
Pi Hydrolysis

The phosphatidylinositol (PI) hydrolysis signaling system has been shown to be altered in platelets of depressed and schizophrenic subjects. Inositol (1,4,5) trisphosphate (Ins(1,4,5)P3), an integral component of the PI signaling system, mobilizes Ca2+ by activating Ins(1,4,5)P3 receptors. To eventually investigate the role of Ins(1,4,5)P3 receptors in depression and other mental disorders, we characterized [H3]Ins(1,4,5)P3 binding sites in crude platelet membranes prepared from small amounts of blood obtained from healthy human control subjects. We found a single, saturable binding site for [H3]Ins(1,4,5)P3 to crude platelet membranes, which is time dependent and modulated by pH, inositol phosphates, and heparin. Since cyclic adenosine monophosphate (cAMP) and Ca2+ have been shown to be important modulators in Ins(1,4,5)P3 receptors, in the present study we also determined the effects of various concentrations of CaCI2 and forskolin on Ins(1,4,5)P3 binding to platelet membranes. CaCI2 modulated [3H]Ins(1,4,5)P3 binding sites in a biphasic manner: at lower concentrations it inhibited [3H]Ins(1,4,5)P3 binding, whereas at higher concentrations, it stimulated [3H]Ins(1,4,5)P3 binding. On the other hand, forskolin inhibited [3H]Ins(1,4,5)P3 binding. Our results thus suggest that the pharmacological characteristics of [3H]Ins(1,4,5)P3 binding to crude platelet membranes are similar to that of Ins(1,4,5)P3 receptors; and that both Ca2+ and cAMP modulate [3H]Ins(1,4,5)P3 binding in crude platelet membranes.

Progesterone increases basal 3′,5′-cyclic adenosine monophosphate formation and down-regulates the agonist-induced inositol phosphates generation in human term placenta

1992 ◽  
Vol 127 (6) ◽  
pp. 499-503
Author(s):  
Jose Rivera ◽  
Andres Lopez Bernal ◽  
Antonio Cano
Keyword(s):  
Angiotensin Ii ◽  
Inositol Phosphates ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Exchange Chromatography ◽  
Target Tissue ◽  
Camp Content ◽  
Human Term Placenta ◽  
Term Placenta

Whether the placenta is a target tissue for estrogens and progesterone, and their putative mechanism of action, is still a controversial question in the literature. The effect of progesterone and estradiol on 3′,5′-cyclic adenosine monophosphate (cAMP) and inositol phosphates generation in human term placenta was investigated. Placental explants were incubated in vitro for up to 48 h in the absence and in the presence of estradiol, progesterone or both steroids (0.1 μmol/l final concentration in all cases), and were stimulated with terbutaline, a β-adrenergic agonist, (0.1 mmol/l) or angiotensin II(1 μmol/l), The cAMP content was measured by a competitive protein binding assay, and the generation of labelled inositol phosphates formation in explants prelabelled with 3H-myo-inositol was measured by anion exchange chromatography. Progesterone increased significantly basal cAMP concentrations in comparison with control or estradiol-treated tissues (169±13, 72±8, and 69±2 pmol/g wet wt tissue, mean±sem, respectively). However, following terbutaline stimulation cAMP levels (mean±sem) increased to similar values under all conditions (182±33, 197±36, and 237±17 pmol/g wet wt tissue for control, estradiol-, and progesterone-treated tissues, respectively). Angiotensin II stimulated inositol phosphates generation in placental explants by an average of fivefold, but this increase was significantly reduced in the presence of progesterone (5.2±0.7, 3.7±0.4, and 2.2±0.3 fold increase vs non-angiotensin-stimulated tissues, for control, estradiol-, and progesterone-treated placenta, mean±sem, respectively). These data suggest that progesterone modulates the formation of second messengers in human placenta at term.

scholarly journals Lens Connexin Channels Show Differential Permeability to Signaling Molecules

2020 ◽  
Vol 21 (18) ◽  
pp. 6943
Author(s):  
Peter R. Brink ◽  
Virginijus Valiunas ◽  
Thomas W. White
Keyword(s):  
Gap Junction ◽  
Inositol Phosphates ◽  
Second Messengers ◽  
Cyclic Adenosine Monophosphate ◽  
Transgenic Animals ◽  
Adenosine Monophosphate ◽  
Signaling Molecules ◽  
Gap Junction Channels ◽  
Connexin Genes

Gap junction channels mediate the direct intercellular passage of small ions as well as larger solutes such as second messengers. A family of proteins called connexins make up the subunits of gap junction channels in chordate animals. Each individual connexin forms channels that exhibit distinct permeability to molecules that influence cellular signaling, such as calcium ions, cyclic nucleotides, or inositol phosphates. In this review, we examine the permeability of connexin channels containing Cx43, Cx46, and Cx50 to signaling molecules and attempt to relate the observed differences in permeability to possible in vivo consequences that were revealed by studies of transgenic animals where these connexin genes have been manipulated. Taken together, these data suggest that differences in the permeability of individual connexin channels to larger solutes like 3′,5′-cyclic adenosine monophosphate (cAMP) and inositol 1,4,5-trisphosphate (IP3) could play a role in regulating epithelial cell division, differentiation, and homeostasis in organs like the ocular lens.

Inositol lipids and phosphates in the regulation of the growth and differentiation of haemopoietic and other cells

1990 ◽  
Vol 327 (1239) ◽  
pp. 193-207 ◽  
Keyword(s):  
Growth Factor ◽  
B Lymphocytes ◽  
Tyrosine Kinases ◽  
Inositol Phosphates ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Interleukin 4 ◽  
Inositol Polyphosphates ◽  
Promote Cell Proliferation ◽  
Inositol Lipids

Stimulation of phosphatidylinositol 4,5-bisphosphate hydrolysis is an important signalling reaction involved in the responses of cells to some, but not all, stimuli that promote cell proliferation. Active agents in this regard include antigens activating T and B lymphocytes, angiotensin (employing a receptor encoded by the mas oncogene), bombesin and platelet-derived growth factor PDGF). However, accumulating evidence suggests that inositol lipids and phosphates also have other roles in the regulation of cell growth and differentiation. Growth factor receptors that encode tyrosine kinases (such as that for PDGF) activate a kinase that synthesises phosphatidylinositol 3-phosphate, a novel lipid, and loss of this kinase-activating function abolishes growth-promoting activity. Human interleukin-4, a lymphokine that activates B lymphocytes, appears to employ phosphatidylinositol 4,5-bisphosphate hydrolysis as a brief initial signal that is followed by a sustained rise in cyclic adenosine monophosphate (cAMP): both signals are needed for the successful induction of the surface antigen CD23. Moreover, the same inositol lipid signalling pathway as is employed by antigen-stimulated mature T lymphocytes to provoke proliferation may be redeployed in immature T cells to trigger their elimination when they encounter self-antigens. Finally, studies of HL60 promyelocytic cells have shown that these cells contain high concentrations of inositol 3,4,5,6-tetrakisphosphate, 1,3,4,5,6-pentakisphosphate and hexakisphosphate, three inositol polyphosphates that are probably formed independently of inositol lipid metabolism. When these cells are induced to differentiate either towards neutrophils (in the presence of dimethylsulphoxide) or macrophages (in phorbol myristate acetate), cessation of growth and acquisition of differentiated characteristics are accompanied by large and different changes in the concentrations of these inositol phosphates that may be characteristic of these two pathways of differentiation.

scholarly journals Regulation of glycoprotein IIB/IIIA exposure on platelets stimulated with alpha-thrombin

Blood ◽  
1992 ◽  
Vol 79 (1) ◽  
pp. 82-90 ◽  
Author(s):  
G van Willigen ◽  
JW Akkerman
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Binding Sites ◽  
Platelet Activating Factor ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Kinase C ◽  
Protein Kinase C Inhibitor

Previous studies have shown that binding sites for fibrinogen on platelets stimulated with platelet-activating factor (PAF), adenosine diphosphate or epinephrine rapidly close in the absence of fibrinogen. In the present study we investigated whether alpha-thrombin induced similar changes in the glycoprotein (GP) IIB/IIIA-complex. Whereas 80% of binding sites exposed by PAF closed within 30 minutes (22 degrees C), alpha-thrombin (0.1 U/mL) triggered long-lasting exposure of binding sites for [125I]-fibrinogen and [125I]-fibronectin. Even removal of alpha-thrombin with an excess of hirudin failed to close the binding sites. Similar to PAF, alpha-thrombin-exposed sites rapidly closed after addition of the protein kinase C inhibitor staurosporine (1 mumol/L) or dibutyryl cyclic adenosine monophosphate (250 mumol/L). In contrast, prostacyclin (PGI2, 10 ng/mL), which induced rapid closure of binding sites in platelets stimulated with PAF, failed to close the sites in alpha-thrombin-treated platelets. Removal of alpha-thrombin from the platelets restored the PGI2-sensitivity. These data indicate that a short interaction between alpha-thrombin and platelets triggers long-lasting exposure of GPIIB/IIIA. Furthermore, as long as alpha- thrombin remains bound to the platelets, agonists that activate the PGI2-receptor are unable to close GPIIB/IIIA.

scholarly journals Regulation of glycoprotein IIB/IIIA exposure on platelets stimulated with alpha-thrombin

Blood ◽  
1992 ◽  
Vol 79 (1) ◽  
pp. 82-90 ◽  
Author(s):  
G van Willigen ◽  
JW Akkerman
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Binding Sites ◽  
Platelet Activating Factor ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Kinase C ◽  
Protein Kinase C Inhibitor

Abstract Previous studies have shown that binding sites for fibrinogen on platelets stimulated with platelet-activating factor (PAF), adenosine diphosphate or epinephrine rapidly close in the absence of fibrinogen. In the present study we investigated whether alpha-thrombin induced similar changes in the glycoprotein (GP) IIB/IIIA-complex. Whereas 80% of binding sites exposed by PAF closed within 30 minutes (22 degrees C), alpha-thrombin (0.1 U/mL) triggered long-lasting exposure of binding sites for [125I]-fibrinogen and [125I]-fibronectin. Even removal of alpha-thrombin with an excess of hirudin failed to close the binding sites. Similar to PAF, alpha-thrombin-exposed sites rapidly closed after addition of the protein kinase C inhibitor staurosporine (1 mumol/L) or dibutyryl cyclic adenosine monophosphate (250 mumol/L). In contrast, prostacyclin (PGI2, 10 ng/mL), which induced rapid closure of binding sites in platelets stimulated with PAF, failed to close the sites in alpha-thrombin-treated platelets. Removal of alpha-thrombin from the platelets restored the PGI2-sensitivity. These data indicate that a short interaction between alpha-thrombin and platelets triggers long-lasting exposure of GPIIB/IIIA. Furthermore, as long as alpha- thrombin remains bound to the platelets, agonists that activate the PGI2-receptor are unable to close GPIIB/IIIA.

Mechanisms of ATP to cAMP Conversion Catalyzed by the Mammalian Adenylyl Cyclase: A Role of Magnesium Coordination Shells and Proton Wires

2019 ◽  
Author(s):  
Bella Grigorenko ◽  
Igor Polyakov ◽  
Alexander Nemukhin
Keyword(s):  
Adenylyl Cyclase ◽  
Bond Cleavage ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Md Simulations ◽  
Coordination Shell ◽  
Energy Profile ◽  
One Step ◽  
Type V

<p>We report a mechanism of adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP) conversion by the mammalian type V adenylyl cyclase revealed in molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) simulations. We characterize a set of computationally derived enzyme-substrate (ES) structures showing an important role of coordination shells of magnesium ions in the solvent accessible active site. Several stable six-fold coordination shells of Mg<sub>A</sub><sup>2+ </sup>are observed in MD simulations of ES complexes. In the lowest energy ES conformation, the coordination shell of Mg<sub>A</sub><sup>2+ </sup>does not include the O<sub>δ1</sub> atom of the conserved Asp440 residue. Starting from this conformation, a one-step reaction mechanism is characterized which includes proton transfer from the ribose O<sup>3'</sup>H<sup>3' </sup>group in ATP to Asp440 via a shuttling water molecule and P<sup>A</sup>-O<sup>3A</sup> bond cleavage and O<sup>3'</sup>-P<sup>A</sup> bond formation. The energy profile of this route is consistent with the observed reaction kinetics. In a higher energy ES conformation, Mg<sub>A</sub><sup>2+</sup> is bound to the O<sub>δ1</sub>(Asp440) atom as suggested in the relevant crystal structure of the protein with a substrate analog. The computed energy profile initiated by this ES is characterized by higher energy expenses to complete the reaction. Consistently with experimental data, we show that the Asp440Ala mutant of the enzyme should exhibit a reduced but retained activity. All considered reaction pathways include proton wires from the O<sup>3'</sup>H<sup>3' </sup>group via shuttling water molecules. </p>

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