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

scholarly journals [Leu]enkephalin stimulates carbohydrate metabolism in isolated hepatocytes and kidney tubule fragments by interaction with angiotensin II receptors

1989 ◽  
Vol 257 (3) ◽  
pp. 705-710 ◽  
Author(s):  
S K Hothi ◽  
D P Randall ◽  
M A Titheradge
Keyword(s):  
Angiotensin Ii ◽  
Carbohydrate Metabolism ◽  
Plasma Membranes ◽  
Isolated Hepatocytes ◽  
Opioid Peptide ◽  
Cross Reactivity ◽  
Angiotensin Ii Receptors ◽  
Kidney Tubule ◽  
Angiotensin Ii Receptor

The possibility that the effects of [Leu]enkephalin in vitro on hepatic carbohydrate metabolism are mediated by interaction with angiotensin II receptors has been examined. Preincubation of hepatocytes with either the angiotensin II receptor antagonist [Sar1,Ile8]angiotensin II or 10 mM-dithiothreitol abolished the ability of both angiotensin II and [Leu]enkephalin to increase phosphorylase a in hepatocytes prepared from fed rats. Dithiothreitol had no effect on the stimulation of phosphorylase in the presence of glucagon or phenylephrine, although it also inhibited the response to vasopressin. [Leu]enkephalin displaced specifically bound 125I-labelled angiotensin II from hepatic plasma membranes over a concentration range of 10(-7)-10(-5) M. This correlated with the dose-response required to stimulate phosphorylase activity in intact hepatocytes and suggests that the effects of the opioid peptides on carbohydrate metabolism in liver are the result of cross-reactivity of the peptides with angiotensin II receptors. Addition of 10(-5) M-[Leu]enkephalin to isolated kidney tubule fragments stimulated gluconeogenesis from 5 mM-pyruvate, the magnitude of stimulation being comparable to that by either angiotensin II or adrenaline. This effect of the opioid peptide was also abolished by pretreatment of the tubules with [Sar1,Ile8]angiotensin II, suggesting that the ability of [Leu]enkephalin to interact with angiotensin II receptors is not restricted to the liver, but may occur in other tissues where both receptors occur together.

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.

Downregulation of hepatocyte P2-purinoceptor binding capacity after trauma-hemorrhage/resuscitation

1994 ◽  
Vol 266 (6) ◽  
pp. R1804-R1809
Author(s):  
M. S. Mahmoud ◽  
P. Wang ◽  
S. R. Hootman ◽  
S. S. Reich ◽  
I. H. Chaudry
Keyword(s):  
Dissociation Constants ◽  
Binding Capacity ◽  
Isolated Hepatocytes ◽  
Scatchard Analysis ◽  
Midline Laparotomy ◽  
Binding Characteristics ◽  
Shed Blood ◽  
P2 Purinoceptors ◽  
Altered Glucose ◽  
Affinity Receptor

Although P2-purinoceptors play an important role in the regulation of liver metabolism under normal conditions, it is not known if trauma-hemorrhage and resuscitation have any effects on such receptors. To study this, we performed a 5-cm midline laparotomy (i.e., trauma induced) on rats and then bled them to and maintained them at a mean arterial pressure of 40 mmHg until 40% of maximum bleedout volume was returned in the form of Ringer lactate (RL). The animals were then resuscitated with 3x the volume of shed blood with RL over 45 min followed by 2x RL over 95 min. Hepatocytes were isolated at the time of maximum bleedout or at 0, 4, 17, and 27 h after the completion of crystalloid resuscitation. P2-purinoceptor binding characteristics were determined in the isolated hepatocytes by using [alpha-35S]ATP. Scatchard analysis revealed high- and low-affinity components of P2-purinoceptors in hepatocytes from sham-operated as well as hemorrhaged and resuscitated animals. The maximum binding capacity (Bmax) of the high-affinity receptor component decreased at the time of maximum bleedout and at 4, 17, and 27 h after resuscitation. In addition to this, the Bmax of low-affinity receptor components also decreased at 4-27 h after resuscitation. In contrast, the dissociation constants of both receptor components were not altered. Because hemorrhagic shock produces abnormalities in glucose metabolism, the downregulation of hepatocyte P2-purinoceptor Bmax may be responsible for the altered glucose homeostasis under such conditions.

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

Reduced number of angiotensin II receptors on platelets in insulin-dependent diabetes

1986 ◽  
Vol 71 (2) ◽  
pp. 217-220 ◽  
Author(s):  
J. M. C. Connell ◽  
Yu-An Ding ◽  
B. M. Fisher ◽  
B. M. Frier ◽  
P. F. Semple
Keyword(s):  
Angiotensin Ii ◽  
Type I Diabetes ◽  
Plasma Concentrations ◽  
Normal Subjects ◽  
Insulin Dependent Diabetes ◽  
Angiotensin Ii Receptors ◽  
Diabetic Patients ◽  
Type I ◽  
Angiotensin Ii Receptor ◽  
Insulin Dependent

1. Angiotensin II receptors on platelets were studied in 13 patients with uncomplicated type I diabetes mellitus and in 15 age-matched normal subjects. 2. Receptor density on cells from the diabetic patients was 15% lower than the normal subjects (5.2 ± 0.8 sd sites/platelet in diabetic patients and 6.4 ± 0.8 in normals, P < 0.001), but there were no differences in receptor affinity as measured by Kd (4.9 ± 1.5 × 10−10 mol/l in diabetic patients and 5.4 ± 1.4 × 10−10 mol/l in normals). 3. Plasma concentrations of renin and angiotensin II were similar in both groups. 4. The reduced density of angiotensin II receptors on platelets from patients with insulin-dependent diabetes may reflect a generalized abnormality of angiotensin II receptor regulation.

Modulation by β-adrenoceptors and angiotensin II receptors of splanchnic nerve evoked catecholamine release from the adrenal medulla

1991 ◽  
Vol 69 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Sylvain Foucart ◽  
Jacques de Champlain ◽  
Réginald Nadeau
Keyword(s):  
Electrical Stimulation ◽  
Angiotensin Ii ◽  
Adrenal Medulla ◽  
Nerve Stimulation ◽  
Enzyme Inhibitor ◽  
Splanchnic Nerve ◽  
Angiotensin Ii Receptors ◽  
Angiotensin Ii Receptor ◽  
Adrenoceptor Antagonist ◽  
Splanchnic Nerve Stimulation

In the present study, we have evaluated the effect of both facilitatory β2-adrenoceptor and angiotensin II receptor on the release of adrenal catecholamines induced by electrical stimulation of the splanchnic nerve in anaesthetized and vagotomized dog. In these experiments, individual or combined treatments with the β2-adrenoceptor antagonist ICI 118551 (0.3 mg/kg i.v.), the converting enzyme inhibitor captopril (2 mg/kg i.v.), or the angiotensin II receptor antagonist saralasin (2 μg∙kg−1∙min−1 i.v.) were found to significantly decrease the release of adrenal catecholamines during splanchnic nerve stimulation (5-V pulses of 2 ms duration for 3 min at 1 Hz) whatever the order of administration of the drugs. On the other hand, the infusion of angiotensin II (20 ng∙kg−1∙min−1) was shown to potentiate the release of adrenal catecholamines in response to electrical stimulation, and this effect was totally blocked by treatment with saralasin (4 μg kg−1∙min−1 i.v.). This facilitating angiotensin mechanism differed from β-adrenoceptor facilitating mechanism, since following β-blockade with ICI 118551, angiotensin II infusion still significantly potentiated the release of catecholamines during splanchnic nerve stimulation. These observations thus suggest that both facilitating β2-adrenoceptors and angiotensin II receptors can independently modulate the release of adrenal catecholamines.Key words: adrenal catecholamines, β2-adrenoceptors, angiotensin II receptors, adrenal medulla, facilitating sympathetic mechanisms, receptor interactions.

scholarly journals Binding of insulin to bovine liver plasma membrane. Use of insulin analogues modified at the A1 residue

1980 ◽  
Vol 186 (3) ◽  
pp. 945-952 ◽  
Author(s):  
Peter Rösen ◽  
Martina Simon ◽  
Hans Reinauer ◽  
Heinz J. Friesen ◽  
Cornelia Diaconescu ◽  
...  
Keyword(s):  
Rat Liver ◽  
Plasma Membranes ◽  
Incubation Temperature ◽  
Biological Activities ◽  
Bovine Liver ◽  
Insulin Binding ◽  
Close Correlation ◽  
Dissociation Rate ◽  
Scatchard Analysis ◽  
Binding Characteristics

Bovine liver plasma membranes [Rösen, Ehrich, Junger, Bubenzer & Kühn (1979) Biochim. Biophys. Acta587, 593–605] show similar insulin-binding characteristics, as evaluated by Scatchard analysis, to those of membrane systems from other species. However, the dissociation rate of bound insulin cannot be accelerated by the addition of insulin, in contrast with membranes isolated from rat liver. The dissociation rate is strongly dependent on the pH. Although dependent on temperature, the total capacity of binding sites is minimally changed, but the number of high-affinity sites is increased 2–3-fold, by lowering the incubation temperature. These data might be interpreted by assuming a single population of receptors whose distribution between different affinity states depends on temperature. In competition studies, most of the modified insulins examined show a close correlation between binding, determined in plasma membranes from bovine liver, and biological activity, measured in adipocytes. The hypothesis that a positive charge on the A1 residue may be favourable for binding is supported by experiments with an isosteric pair of insulins modified at this residue ([carbamoyl-GlyA1]- and [amidino-GlyA1]insulin) and with modified insulins carrying one or more positive charges on the A1 residue ([Arg-GlyA1]-, [Arg-Arg-GlyA1]-, [Arg-Arg-Arg-GlyA1]- and [Lys-Arg-GlyA1]insulin). The latter insulin derivatives show a higher binding activity for plasma membranes from bovine, porcine and rat liver than expected from their biological activities in adipocytes.

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