scholarly journals The liver angiotensin receptor involved in the activation of glycogen phosphorylase

1982 ◽  
Vol 208 (3) ◽  
pp. 809-817 ◽  
Author(s):  
Stefaan Keppens ◽  
Henri De Wulf ◽  
Pascale Clauser ◽  
Serge Jard ◽  
Jean-Louis Morgat
Keyword(s):  
Biological Activity ◽  
Rate Constant ◽  
Glycogen Phosphorylase ◽  
Plasma Membranes ◽  
Binding Capacity ◽  
Rat Hepatocytes ◽  
Dissociation Rate ◽  
Biologically Active ◽  
Maximal Binding ◽  
Highly Correlated

Specific angiotensin binding to rat hepatocytes and purified liver plasma membranes was measured by using biologically active [3H]angiotensin (sp. radioactivity 14Ci/mmol). The kinetic parameters for angiotensin binding to hepatocytes are: K+1 (association rate constant). 100μm−1·min−1; K–1 (dissociation rate constant), 2min−1; Kd (dissociation constant). 30nm; maximal binding capacity, 0.42pmol/106 cells or 260000 sites/cell. Angiotensin binding to membranes is profoundly affected by GTP (0.1mm) and NaCl (100mm); these regulatory compounds greatly enhance both the rate of association and of dissociation and also the extent of dissociation. Kd amounts to 10nm in the presence of GTP+NaCl and to 1.5nm in their absence; maximal binding capacity is 0.70pmol/mg of protein, both with or without GTP+NaCl. The relative affinities of 11 angiotensin structural analogues were deduced from competition experiments for [3H]angiotensin binding to hepatocytes and to membranes (in the latter case, GTP + NaCl were not included, in order to study the higher affinity state of the receptor). These are highly correlated with their biological activity (activation of glycogen phosphorylase in hepatocytes). Binding to membranes occurs in the same concentration range as the biological effect. On the other hand, the existence of numerous spare receptors is suggested by the observation that binding of the agonists to hepatocytes requires 25-fold higher concentrations than those needed for their biological activity. These data clearly suggest that the detected binding sites correspond to the physiological receptors involved in the glycogenolytic action of angiotensin on rat liver.

The angiotensin II receptor of rabbit liver: characterization in isolated hepatocytes and effect of GTP

1989 ◽  
Vol 123 (1) ◽  
pp. 131-136 ◽  
Author(s):  
A. Vandekerckhove ◽  
S. Keppens ◽  
H. De Wulf
Keyword(s):  
Angiotensin Ii ◽  
Rate Constant ◽  
Plasma Membranes ◽  
Binding Capacity ◽  
Isolated Hepatocytes ◽  
Dissociation Rate ◽  
Angiotensin Ii Receptors ◽  
Angiotensin Ii Receptor ◽  
Binding Characteristics ◽  
Binding Data

ABSTRACT A homologous population of specific angiotensin II receptors is present on the cell surface of isolated rabbit hepatocytes. The binding characteristics of [3H]angiotensin II to the cells were: association rate constant (K+1) 0·08 l/nmol per min and dissociation rate constant (K−1) 1·9/min, yielding a dissociation constant (Kd) of 24 nmol/l. A very similar Kd (32 nmol/l) has been derived from saturation binding data which indicate a maximal binding capacity of about 200 000 sites/cell. Analysis of the association binding data to purified liver plasma membranes indicated a Kd of 6 nmol/l in the absence and 30 nmol/l in the presence of GTP. Dissociation was clearly dependent upon the presence of the nucleotide, which shifted the K−1 from 0·12/min to 0·42/min. The studied binding sites are very likely to be involved in the glycogenolytic action of angiotensin II, since a highly significant correlation was established between the biological activity (activation of glycogen phosphorylase) and the binding affinity of a series of agonistic analogues. The reported characteristics of the rabbit hepatic angiotensin II receptors show much similarity with those of rat liver. Journal of Endocrinology (1989) 123, 131–136

Agonist-induced internalisation of the angiotensin II-binding sites from plasma membranes of isolated rat hepatocytes

1997 ◽  
Vol 152 (3) ◽  
pp. 407-412 ◽  
Author(s):  
M Montiel ◽  
M C Caro ◽  
E Jiménez
Keyword(s):  
Plasma Membrane ◽  
Angiotensin Ii ◽  
Binding Sites ◽  
Plasma Membranes ◽  
Binding Capacity ◽  
Rat Hepatocytes ◽  
Receptor Complex ◽  
Ang Ii ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

Angiotensin II (Ang II) provokes rapid internalisation of its receptor from plasma membranes in isolated rat hepatocytes. After 10 min stimulation with Ang II, plasma membrane lost about 60% of its 125I-Ang II-binding capacity. Internalisation was blocked by phenylarsine oxide (PhAsO), whereas okadaic acid, which markedly reduced the sustained phase of calcium mobilization, did not have a preventive effect on Ang II–receptor complex sequestration. These data suggest that Ang II receptor internalisation is probably independent of a phosphorylation/dephosphorylation cycle of critical serine/threonine residues in the receptor molecule. To establish a relationship between sequestration of the Ang II receptor and the physical properties of the Ang II-binding sites, 125I-Ang II–receptor complex profiles were analysed by isoelectric focusing. In plasma membrane preparations two predominant Ang II-binding sites, migrating to pI 6·8 and 6·5 were found. After exposure to Ang II, cells lost 125I-Ang II-binding capacity to the Ang II–receptor complex migrating at pI 6·8 which was prevented in PhAsO-treated cells. Pretreatment of hepatocytes with okadaic acid did not modify Ang II–receptor complex profiles, indicating that the binding sites corresponding to pI 6·5 and pI 6·8 do not represent a phosphorylated and/or non-phosphorylated form of the Ang II receptor. The results show that the Ang II–receptor complex isoform at pI 6·8 represents a functional form of the type-1 Ang II receptor. Further studies are necessary to identify the Ang II-related nature of the binding sites corresponding to pI 6·5. Journal of Endocrinology (1997) 152, 407–412

scholarly journals Characterization of the liver P2-purinoceptor involved in the activation of glycogen phosphorylase

1986 ◽  
Vol 240 (2) ◽  
pp. 367-371 ◽  
Author(s):  
S Keppens ◽  
H De Wulf
Keyword(s):  
Binding Sites ◽  
Glycogen Phosphorylase ◽  
Plasma Membranes ◽  
Specific Binding ◽  
Rank Order ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
P2 Purinoceptors

Evidence has been presented for the existence in rat liver of P2-purinoceptors which are involved in the control of glycogenolysis. Isolated rat hepatocytes and purified liver plasma membranes have been used to study the binding of the ATP analogue adenosine 5′-[alpha- [35S]thio]triphosphate (ATP alpha [35S]) to these postulated P2-purinoceptors. The nucleotide analogue behaves as a full agonist for the activation of glycogen phosphorylase in isolated hepatocytes, 0.3 microM being required for half-maximal activation. Specific binding of ATP alpha [35S] to hepatocytes and plasma membranes occurs within 1 min and is essentially reversible. The analysis of the dose-dependency at equilibrium indicates the presence of binding sites with Kd of 0.23 microM with hepatocytes and Kd of 0.11 microM with plasma membranes. The relative affinities of 10 nucleotide analogues were deduced from competition experiments for ATP alpha [35S] binding to hepatocytes, and these correlated highly with their biological activity (activation of glycogen phosphorylase in hepatocytes). For all the agonists, binding occurs in the same concentration range as the biological effect. These data clearly suggest that the detected binding sites correspond to the physiological P2-purinoceptors involved in the regulation of liver glycogenolysis. The rank order of potency of some ATP analogues suggests that liver possesses the P2Y-subclass of P2-purinoceptors.

Characterization of glucagon and catecholamine effects on isolated sheep hepatocytes

1988 ◽  
Vol 255 (4) ◽  
pp. R539-R546
Author(s):  
C. Morand ◽  
C. Yacoub ◽  
C. Remesy ◽  
C. Demigne
Keyword(s):  
Rat Liver ◽  
Glycogen Phosphorylase ◽  
Plasma Membranes ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Cyclic Monophosphate ◽  
Sheep Liver ◽  
Beta Agonists ◽  
Rat Liver Cells

The purpose of this study was to characterize the glycogenolytic response to catecholamines and glucagon in isolated sheep hepatocytes. In this species, epinephrine appeared to exert its action on hepatic glycogenolysis by altering the cytosolic concentrations of both adenosine 3',5'-cyclic monophosphate (cAMP) and Ca2+. In contrast to results obtained in rat hepatocytes, glucagon failed to induce a rise in free cytosolic Ca2+ in sheep liver. Experiments on isolated hepatocytes or on liver plasma membranes showed that in sheep, glucagon was more efficient than epinephrine in promoting the production of cAMP. In the presence of glucagon or epinephrine, the activation of the glycogen phosphorylase a always appeared greater in sheep than in rat liver cells, whereas the variations in cellular cAMP were quite limited in sheep. The alpha 1- and beta-agonists (phenylephrine and isoproterenol) were alone as efficient as epinephrine in promoting phosphorylase a activation in sheep hepatocytes. All these results indicate the existence in sheep liver of a glycogen phosphorylase highly responsive to hormones.

scholarly journals Characterization of human somatotropin binding to detergent-solubilized lactogenic receptors from rat liver

1981 ◽  
Vol 194 (2) ◽  
pp. 385-394 ◽  
Author(s):  
J S Bonifacino ◽  
S H Sánchez ◽  
A C Paladini
Keyword(s):  
Rat Liver ◽  
Rate Constant ◽  
Binding Capacity ◽  
Inhibitory Effect ◽  
Binding Activity ◽  
Dissociation Rate ◽  
Scatchard Analysis ◽  
Single Class ◽  
Solubilized Form ◽  
Triton X

Lactogenic receptors from rat liver microsomal fraction (‘microsomes’) were extracted by treatment with 1% (w/v) Triton X-100. Triton X-100 exerts an inhibitory effect on both the binding reaction and the separation of the free hormone from the complex. The association and dissociation of 125I-labelled human somatotropin are time- and temperature-dependent processes. The association rate constant, k1, is 6.7 × 10(6) mol . litre-1 . min-1 at 25 decrees C, and the dissociation rate constant, k-1, is 1.1 × 10(-3) min-1 at 25 degrees C. Scatchard analysis of saturation data reveals the existence of a single class of receptors and that solubilization leads to a slight decrease in affinity and a sharp increase in binding capacity. The dissociation constant, Kd, of the solubilized preparation is 0.22 nM and the binding capacity 2900 fmol/mg of protein. Similar results were obtained from competition experiments. Binding of 125I-labelled human somatotropin to the solubilized receptors is specifically inhibited by hormones with lactogenic activity. Incubation of the solubilized preparation with trypsin resulted in an 80% decrease in binding activity. The solubilized form of the receptor has a slightly increased sensitivity to the inactivation by trypsin, heat and extremes of pH, with respect to the membrane-bound form.

Hypersensitivity to Thromboxane A2 in Cholesterol-Rich Human Platelets

1990 ◽  
Vol 64 (04) ◽  
pp. 594-599 ◽  
Author(s):  
Takuya Tomizuka ◽  
Kyohei Yamamoto ◽  
Aizan Hirai ◽  
Yasushi Tamura ◽  
Sho Yoshida
Keyword(s):  
Calcium Concentration ◽  
Binding Capacity ◽  
Thromboxane A2 ◽  
Cytosolic Calcium ◽  
Cholesterol Content ◽  
Human Platelets ◽  
Dissociation Rate ◽  
Platelet Membrane ◽  
Maximal Concentration ◽  
Equilibrium Dissociation

SummaryThe effect of changes in platelet membrane cholesterol content on thromboxane A2 (TXA2)-induced platelet activation was studied. Concentrations of 9,ll-epithio-ll,12-methano-TXA2 (STA2), a stable analogue of TXA2 which can cause half-maximal aggregation and release of [14C]serotonin in cholesterol-rich platelets were significantly lower than those in cholesterol-normal platelets. STA2-induced increase in cytosolic calcium concentration and [32P]phosphatidic acid formation in cholesterol-rich platelets were significantly greater than those in cholesterol-normal platelets. The maximal concentration of binding site (Bmax) for SQ29548 was significantly increased in cholesterol-rich platelets compared with cholesterol-normal platelets, while the equilibrium dissociation rate constant (Kd) for SQ29548 did not differ between cholesterol-rich and cholesterol-normal platelets. The present study suggested that sensitivity to TXA2 was increased by the incorporation of cholesterol into platelet membrane and that the cause of hypersensitivity to TXA2 in cholesterol-rich platelets may be partly explained by an increase in binding capacity for TXA2.

PLASMA CORTISOL, CORTICOSTERONE AND NON-PROTEIN-BOUND CORTISOL IN EXTRACORPOREAL CIRCULATION

1972 ◽  
Vol 69 (3) ◽  
pp. 517-525 ◽  
Author(s):  
T. Uozumi ◽  
H. Manabe ◽  
Y. Kawashima ◽  
Y. Hamanaka ◽  
Y. Monden ◽  
...  
Keyword(s):  
Cortisol Level ◽  
Extracorporeal Circulation ◽  
Plasma Cortisol ◽  
Elevated Level ◽  
Marked Decrease ◽  
Binding Capacity ◽  
Biologically Active ◽  
Major Surgery ◽  
Plasma Samples ◽  
Effective Factor

ABSTRACT The response of plasma cortisol, corticosterone and non-protein-bound cortisol in the extracorporeal circulation was investigated in 14 patients. The pre-perfusion levels of plasma cortisol, corticosterone and non-protein-bound cortisol were significantly elevated. During and immediately after perfusion, the levels of cortisol and corticosterone were found to decrease significantly from the pre-perfusion levels, while the percentage of non-protein-bound cortisol was shown to increase significantly. This indicates a marked decrease in cortisol binding capacity of plasma during extracorporeal circulation. Moreover in 200 plasma samples, it was demonstrated that the cortisol level increased markedly and the cortisol binding capacity decreased slightly during and shortly after major surgery without perfusion. It is concluded that stressful situations in major surgery with or without perfusion are associated with markedly increased levels of biologically active non-protein-bound cortisol. The elevated level of non-protein-bound cortisol in surgery seems to be dependent on the increase in the level of plasma cortisol as well as on the decrease in the cortisol binding capacity of plasma. Although the increased plasma cortisol plays the most important role in surgery with no perfusion, the decreased cortisol binding capacity may be the more effective factor involved during perfusion.

Isoselenocyanates: Synthesis and Their Use for Preparing Selenium-Based Heterocycles

Synthesis ◽  
2021 ◽  
Author(s):  
Stefan H. Bossmann ◽  
Raul Neri
Keyword(s):  
Biological Activity ◽  
Infectious Diseases ◽  
Cancer Cells ◽  
Multicomponent Reactions ◽  
Oxidative Cyclization ◽  
Biologically Active ◽  
Organoselenium Compounds ◽  
X Ray ◽  
Synthetic Work

AbstractIsoselenocyanates (ISCs) are a class of organoselenium compounds that have been recognized as potential chemotherapeutic and chemopreventative agents against cancer(s) and infectious diseases. ISC compounds are chemically analogous to their isosteric relatives, isothiocyanates (ITCs); however, they possess increased biological activity, such as enhanced cytotoxicity against cancer cells. ISCs not only serve as significant products, but also as precursors and essential intermediates for a variety of organoselenium compounds, such as selenium-containing heterocycles, which are biologically active. While syntheses of ISCs have become less difficult to accomplish, the syntheses of selenium-containing heterocycles are often difficult due to the use of highly toxic selenium reagents. Because of this, ISCs can serve as versatile reagents for the preparation of these heterocycles. In this review, the classical and recent syntheses of ISCs will be discussed, along with notable and recent synthetic work employing ISCs to access novel selenium-containing heterocycles.1 Introduction1.1 Selenium and Health2 Isoselenocyanates2.1 Preparation of Isoselenocyanates3 Selenium-Containing Heterocycles3.1 Notable Synthetic Work3.2 Recent Synthetic Work3.2.1 Synthesis of N-(3-Methyl-4-phenyl-3H-selenazol-2-ylidene)benzamide­ Derivatives3.2.2 Synthesis and X-ray Studies of Diverse Selenourea Derivatives3.2.3 Synthesis of Heteroarene-Fused [1,2,4]Thiadiazoles/Selenadiazoles via Iodine-Promoted [3+2] Oxidative Cyclization3.2.4 2-Amino-1,3-selenazole Derivatives via Base-Promoted Multicomponent Reactions4 Conclusion

scholarly journals Isolation, Structure Elucidation, and Biological Activity of a New Alkaloid from Zanthoxylum rhetsa

2011 ◽  
Vol 6 (11) ◽  
pp. 1934578X1100601
Author(s):  
Karsten Krohn ◽  
Stephan Cludius-Brandt ◽  
Barbara Schulz ◽  
Mambatta Sreelekha ◽  
Pottachola Mohamed Shafi
Keyword(s):  
Biological Activity ◽  
Carboxylic Acid ◽  
Medicinal Plant ◽  
Plant Extract ◽  
Structure Elucidation ◽  
Biologically Active ◽  
Reduction Product ◽  
Pharmacological Properties ◽  
Evergreen Tree

Several biologically active alkaloids (1-4, 6), including a new quinazoline-6-carboxylic acid (1), were isolated from the medicinal plant Zanthoxylum rhetsa, an evergreen tree, native to subtropical areas. Whereas the pharmacological properties of the plant extract and single constituents have been widely tested, we now show that all of the metabolites have antialgal activities, all but 6 are antibacterial, and 6 and the reduction product 5 (derived from 4) are also antifungal.

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