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Query: UMLS:C0004135 (ATM)
 13,001 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Complementary DNAs for angiotensin II type 1 receptor isoforms AT1A and AT1B were cloned by expression cloning from bovine adrenal and rat vascular smooth muscles. Human AT1 receptor was also cloned. Seven transmembrane structures emerged. The AT1 type receptor interacted with more than one type of G-proteins. The ligand binding site of AT1 involving Arg167, Lys199, and Asp263 has been identified by site directed mutagenesis. The regulation of the receptors occur at many stages. The isoform, AT2, was also expression cloned from rat pheochromocytoma cells. Although its ligand binding is not affected by stable GTP analogs, it is a seven transmembrane domain receptor. It mediates the modulations of phosphotyrosine phosphatase by angiotensin II and AT2 specific CGP42112A. The modulation was abolished by pertussis toxin. Thus, AT2 belongs to a new class of angiotensin receptors with unique signalling and regulatory mechanisms. AT1 mediates cellular growth. Interestingly, AT2 expression is inversely related to the mitogenic activity of cells.
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PMID:Cloning, expression and regulation of angiotensin II receptors. 748 33

Most of angiotensin II's (Ang II) documented effects have been attributed to the interaction of this peptide with a G-protein coupled receptor termed AT1. The role and the signalling mechanisms of the more recently characterized AT2 receptor, which does not appear to interact with G-proteins, are however still unclear. We report here that this receptor mediates the rapid dephosphorylation of tyrosine residues of specific proteins in the 60 to 150 KDa range in PC12W cells which express only AT2 receptors. We further characterized this phosphatase activity using the synthetic substrate para-nitrophenyl phosphate. Dephosphorylation of this substrate in response to Ang II is not affected by Ser/Thr phosphatase inhibitors, but is completely prevented by the protein tyrosine phosphatase (PTPase) inhibitor sodium orthovanadate. This effect is mimicked by the AT2 selective agonist CGP42112 and is not affected by the AT1 antagonist losartan, In contrast to the recently reported PTPase stimulation by somatostatin and dopamine, PTPase stimulation by Ang II is not affected by the guanyl nucleotides GTP gamma S and GDP beta S. Moreover, depletion of solubilized membrane preparations from G-proteins by lectin affinity chromatography does not alter Ang II stimulation of the measured PTPase activity. These findings indicate that Ang II stimulates a PTPase activity through AT2 receptors via G-protein independent pathways. This signalling mechanism may be involved in AT2 receptor mediated actions of Ang II such as particulate guanylate cyclase inhibition, modulation of T-type Ca++ channels and regulation of cell proliferation and differentiation.
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PMID:Angiotensin II stimulates protein tyrosine phosphatase activity through a G-protein independent mechanism. 795 93

Angiotensin II (Ang II) is an important regulator of aldosterone production by bovine adrenal glomerulosa (BAG) cells. Ang II interacts with a specific receptor coupled to a guanyl nucleotide-binding protein (G protein) that controls the activity of phospholipase C. A primary culture of BAG cells was used to study short-term desensitization of the Ang II receptor. After short exposures to Ang II, BAG cells lost some [125I]Ang II binding capacity. This loss was dependent on the duration of the pretreatment and on the concentration of Ang II used. A maximal loss of [125I]Ang II binding of 55 +/- 10% was observed after a pretreatment of 30 min with 30 nM Ang II. The EC50 was 1.3 +/- 0.6 nM (mean +/- SD of three experiments). The desensitization was readily reversible, since most of the binding capacity (higher than 90%) was recovered after a 60-min incubation, at 37 C, in the absence of Ang II. Scatchard studies revealed that the Ang II receptor of BAG cells exists under two affinity states with one dissociation constant of 0.2 nM and another dissociation constant of 1.5 nM. After a 30-min exposure of BAG cells to 10 nM Ang II, an important decrease of high affinity binding sites was observed. The maximal amount of binding sites was similar on control and desensitized cells (around 52,000 receptors per cell). GTP gamma S, a potent activator of G proteins, decreased [125I]Ang II binding to permeabilized BAG cells. This GTP gamma S effect was not observed on permeabilized BAG cells that had previously been desensitized with 10 nM Ang II. These results suggested that, similarly to GTP gamma S, short exposure to 10 nM Ang II caused the uncoupling of Ang II receptor from its G protein. DuP-753 (a selective AT1 angiotensin II type 1 receptor antagonist) markedly unhibited, whereas PD-123319 (a selective AT2 angioten II type 2 receptor antagonist) had no effect on Ang II receptor desensitization, indicating that the AT1 receptor subtype was responsible for the observed phenomenon. Pretreatment of BAG cells with staurosporine (a protein kinase C inhibitor) and R24571 (a calmodulin inhibitor) did not modify Ang II-induced desensitization of AT1 receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Short-term desensitization of the angiotensin II receptor of bovine adrenal glomerulosa cells corresponds to a shift from a high to a low affinity state. 795 36

To address conflicting reports concerning the number of angiotensin II (AII) receptor type 1 (AT1) coding loci in vertebrates, Southern blot analysis was used to determine the genomic representation of AT1 receptor genes in animals comprising a divergent evolutionary spectrum. The data demonstrate that the AT1 receptor gene is present as a single genomic copy in a broad spectrum of animals including human, monkey, dog, cow, rabbit, and chicken. In contrast, members of the rodent taxonomic order contain two genes in their genomes. These two genes may have arisen in rodents as a consequence of a gene duplication event that occurred during evolution following the branching of rodents from the mammalian phylogenetic tree. In order to investigate the properties of the human AT1 receptor in a pure cell system, the recombinant human AT1 receptor was stably expressed in mouse L cells. An isolated cell line, designated LhAT1-D6, was found to express abundant levels of recombinant receptor [430 +/- 15 fmol/mg] exhibiting high affinity [KD = 0.15 +/- 0.02 nM] for [125I][SAR1, Ile8] angiotensin II (SIA). The pharmacological profile of ligands competing for [125I] SIA binding to the expressed receptor was in accordance with that of the natural receptor. Radioligand binding of the expressed receptor was decreased in the presence of the non-hydrolyzable analog of GTP, guanosine 5'-(gamma-thio) triphosphate [GTP gamma S]. Angiotensin II evoked a rapid efflux of 45Ca2+ from LhAT1-D6 cells that was blocked by AT1 receptor specific antagonists. In addition, AII inhibited forskolin-stimulated cAMP accumulation in these cells which was blocked by the AT-1 antagonist. Thus, the LhAT1-D6 cell line provides a powerful tool to explore the human AT1 receptor regulation.
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PMID:Human AT1 receptor is a single copy gene: characterization in a stable cell line. 804 68

1. Angiotensin II (AII) reduces blood flow, modulates vascular remodelling and is a growth factor. Human inflammatory arthritides are characterized by synovial hypoperfusion, hypoxia and proliferation. We aimed to localize and characterize receptors for AII in human synovium. 2. We used quantitative in vitro receptor autoradiography with [125I]-(Sar1, Ile8)AII and [125I]-AII on human synovium from patients with chondromalacia patellae, osteoarthritis and rheumatoid arthritis. 3. [125I]-(Sar1, Ile8)AII and [125I]-AII bound to similar sites on synovial blood vessels, lining cells and stroma. Binding to microvessels (< 100 microns diameter) was more dense than to arteriolar media, and vascular binding was more dense than that to lining cells and stroma. 4. Microvessels and arterioles which displayed angiotensin converting enzyme-like immunoreactivity also displayed specific binding of [125I]-(Sar1, Ile8)AII. 5. Specific binding of [125I]-(Sar1, Ile8)AII to each structure was completely inhibited by 10 microM dithiothreitol and was inhibited by unlabelled ligands with the rank order of potency (Sar1, Ile8)AII > AII > losartan = SKF108566 > PD123319 indicating an AT1 subclass of angiotensin receptor. 6. GTP gamma S (1 microM) abolished specific binding of [125I]-AII and abolished the high affinity component of the binding inhibition curve for AII against [125I]-(Sar1, Ile8)AII, indicating G protein coupling. 7. The distribution of [125I]-(Sar1, Ile8)AII binding sites was similar in all disease groups and no significant differences in binding densities, affinities or specificities were observed between disease groups. 8. Locally generated AII may act on synovial AT1 receptors to modulate synovial perfusion and growth. Specific AT1 receptor antagonists should help elucidate the role of angiotensins in human arthritis.
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PMID:AT1 receptor characteristics of angiotensin analogue binding in human synovium. 807 62

Angiotensin II (ANG II) receptor subtypes (AT1, displaced by losartan, and AT2, displaced by CGP 42112A) were characterized by quantitative autoradiography after incubation with the ANG II agonist [125I]Sar1-ANG II, in specific brain nuclei of 19-day-old rat embryos. Binding to AT1 receptors, located in the subfornical organ, paraventricular nucleus, nucleus of the solitary tract and choroid plexus, was sensitive to incubation with GTP gamma S. The sensitivity of AT2 receptors to GTP gamma S was heterogeneous. In the ventral thalamic, rostral hypoglossal and medial geniculate nuclei, and in the locus coeruleus, binding to AT2 receptors was sensitive to GTP gamma S and these areas belong to the AT2A subgroup. Conversely, in the inferior olive, medial (fastigial) cerebellar nucleus and caudal part of the hypoglossal nucleus, areas belonging to the AT2B subgroup, binding was insensitive to GTP gamma S. AT2 receptors were also present in cerebral arteries. In the fetal anterior pituitary, AT1 receptors predominated. The angiotensin-converting enzyme (ACE; EC 3.4.15.1) was studied by autoradiography with the selective inhibitor [125I]351A. In 19-day-old embryos, ACE was highly expressed in choroid plexus, with high concentrations in subfornical organ, posterior pituitary and cerebral arteries. No ACE binding was detected in extrapyramidal structures or anterior pituitary in 19-day-old embryos.
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PMID:Angiotensin II receptor subtypes and angiotensin-converting enzyme in the fetal rat brain. 813 Oct 49

High-affinity (104 +/- 18 pmol/l) and high-density (204 +/- 25 fmol/mg) angiotensin II (AII) binding sites have been identified in Xenopus laevis heart membranes. Competition binding of [125I]Sar1,Ile8 angiotensin (SIA) to these receptors by peptide analogs selective for the mammalian AII receptor subtypes AT1 and AT2 suggested that the amphibian AII binding sites were more closely related to the AT1 receptor subtype. Also in common with AT1 receptors, dithiothreitol and GTP gamma S inhibited [125I]SIA binding to Xenopus heart receptors, exhibiting IC50 values of 600 and 0.95 mumol/l, respectively. In addition, Xenopus oocytes injected with Xenopus heart mRNA were capable of mobilizing calcium when exposed to AII, demonstrating that Xenopus AII receptors are functionally linked to a second-messenger system similar to that coupled to mammalian AT1 receptors. However, in contrast to both AT1 and AT2 receptor subtypes, nonpeptide antagonists DUP 753 and SK&F 108566 (AT1 receptor selective) and PD123319 (AT2 selective) did not bind the Xenopus AII receptors, thus establishing that the amphibian receptors were pharmacologically unique. Together, these results demonstrate that Xenopus heart AII receptors are functionally similar to mammalian AT1 receptors but are pharmacologically distinct from both AT1 and AT2 receptors.
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PMID:Characterization of a functional angiotensin II receptor in Xenopus laevis heart. 817 10

The murine neuroblastoma N1E-115 cell line possesses a high density of angiotensin II (AngII) receptors that can be solubilized with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. These solubilized binding sites exhibited high affinity for CGP-42112A and not Losartan, indicating that they were of the AT2 subtype. However, displacement of 125I-AngII with the AT2 nonpeptide antagonist PD-123319 resulted in a biphasic curve, suggesting heterogeneity of the AT2 receptor population in N1E-115 cells. In support of this view, separation of two receptor populations was accomplished with heparin-Sepharose chromatography. More specifically, three distinct protein peaks eluted from the heparin-Sepharose column, two of which bound 125I-AngII with high affinity and saturability. One of these binding peaks (peak I) eluted rapidly and represented approximately 80% of the total binding activity, whereas the remaining binding activity was contained within a second peak (peak III) that required the addition of 1.5 M NaCl for its complete elution. Pharmacological analysis revealed that both peaks of binding activity were exclusively AT2 receptors insofar as they exhibited high affinity for CGP-42112A and little or no affinity for the AT1-selective antagonist Losartan. However, whereas the nonpeptidic AT2-selective antagonist PD-123319 completely displaced the binding of 125I-AngII from peak I in a monophasic fashion (IC50 = 9.1 +/- 4.1 nM; mean +/- SEM; n = 3), PD-123319 was much less effective in displacing 125I-AngII from peak III (IC50 = 196 +/- 27 nM; mean +/- SEM; n = 3). Treatment of individual peaks with the reducing agent dithiothreitol caused a large increase in 125I-AngII specific binding in peak III, whereas a decrease in binding was observed in peak I. Moreover, GTP gamma S significantly reduced high-affinity agonist binding in peak I but not peak III, further suggesting heterogeneity in the AT2 receptor family. Finally, immunoblotting studies with polyclonal antisera raised against peak I specifically detected two proteins of 110 and 66 kDa, as is true in crude solubilized membranes, whereas no immunospecific proteins were detected in peak III. These same antisera immunoprecipitated 125I-AngII binding activity in peak I but were ineffective in peak III. Collectively, these results suggest that heparin-Sepharose chromatography can efficiently separate two pharmacologically, biochemically and immunologically distinct populations of AT2 receptors.
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PMID:Biochemical characterization of two distinct angiotensin AT2 receptor populations in murine neuroblastoma N1E-115 cells. 818 20

The binding characteristics of radiolabeled angiotensin II and the nonpeptidergic angiotensin AT1 receptor antagonist, DuP 753 (Losartan), were studied in rat liver homogenates. Competition experiments with human angiotensin I, II, and III and with the angiotensin antagonists, CGP 42114A, saralasin, DuP 753, and PD123177, confirmed that the [3H]angiotensin II binding was to an AT1-type receptor. Computer analysis of the competition studies using the human angiotensins demonstrated that the data could be best fitted to a model that considers interaction at two sites. Angiotensin II, angiotensin III, and an angiotensin II analogue, [Sar1]angiotensin II, were calculated to have approximately one hundredfold selectivity at each of the two binding sites, but angiotensin I and the antagonists did not show a difference in affinity between the two sites. The addition of 120 mM NaCl and the nonhydrolyzable analogue of GTP, GppNHp (100 microM) to the buffer resulted in a reduction in [3H]angiotensin II binding at both sites. Thus, we suggest that the two sites may represent distinct angiotensin AT1-type receptors, possibly AT1a and AT1b subtypes. The addition of dithiothreitol (DTT) reduced [3H]angiotensin II binding, confirming the binding to AT1-type receptors. Binding studies using the selective AT1 angiotensin II receptor antagonist, [3H]DuP 753, were also performed on the rat liver homogenates. Saturation studies using both angiotensin II and DuP 753 to define nonspecific binding showed that [3H]DuP 753 bound to at least two types of site, one smaller population of receptors that was sensitive to both angiotensin II and DuP 753 and a second site that was sensitive to DuP 753 only.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Binding of [3H]angiotensin II and [3H]DuP 753 (Losartan) to rat liver homogenates reveals multiple sites. Relationship to AT1a- and AT1b-type angiotensin receptors and novel nonangiotensin binding sites. 823 32

The objective of this study was to determine whether the three isoforms of recombinant Ang II receptors (rAT1A, rAT1B and hAT1), stably and individually expressed in CHO cells, could be pharmacologically distinguished by their ligand binding signatures. Competition studies were performed to characterize the inhibition of [125I]Ang II binding to each of the cell membrane preparations by an extensive series of peptide and nonpeptide Ang II analogs. Scatchard plot analyses revealed the following binding characteristics:rAT1A-Kd = 1.27 +/- 0.14 nM; rAT1B- Site 1:Kd = 0.56 +/- 0.11 nM, Site 2: Kd = 126 +/- 23 nM; and hAT1-Site 1:Kd = 1.06 +/- 0.16 nM, Site 2: Kd = 257 +/- 55 nM. The binding of [125I]Ang II in the three preparations was similarly sensitive to inhibition by GTP gamma S. The ligand binding signatures of the three receptor isoforms are essentially the same and are illustrated by the affinity and order of potency of the following ligands: L-158,809 > or = Sar1, Ile8Ang II > saralasin Ang II > or = Ang III > EXP581 > EXP3174 > losartan > or = EXP811 > GR117,289c > EXP6803 > DuP 532 > Ang I >> PD123177. In conclusion, the two rat AT1 receptor isoforms are pharmacologically indistinguishable from each other and from that of the human.
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PMID:The ligand binding signatures of the rat AT1A, AT1B and the human AT1 receptors are essentially identical. 826 79


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