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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The octapeptide angiotensin II mediates the physiological actions of the renin-angiotensin system through activation of several angiotensin II receptor subtypes; in particular the AT1. In many tissues, the presence of multiple angiotensin II receptor subtypes, together with a low number of receptors, makes it difficult to study biological responses to physiological concentrations (10(-11)-10(-9) M) of angiotensin II. Also, cultured cells show diminished angiotensin II receptor binding with respect to time in culture and passage number. To address these problems, we expressed the recombinant AT1A receptor in CHO-K1 cells. The stably transfected receptor was characterized using radioligand binding studies and functional coupling to cytosolic free calcium. Radioligand binding of [125I] angiotensin II to the angiotensin II receptor was specific, saturable, reversible and modulated by guanine nucleotides. Like the endogenous AT1A receptor, reported in a variety of tissues, the specific, noncompetitive, nonpeptide AII receptor antagonist, EXP3174, blocked binding of [125I] angiotensin II to the transfected receptor. Scatchard analysis demonstrated that the transfected receptor had a dissociation constant of 1.9 nM with a density of 3.4 pmol/mg protein. An important feature of many of the responses to angiotensin II is the rapid desensitization that occurs following agonist occupancy and the development of tachyphylaxis. In AT1A receptor transfected CHO-K1 cells, angiotensin II (10(-9) M) stimulated a rapid increase in cytosolic free calcium that was completely desensitized within 50 sec following receptor occupancy. Agonist induced desensitization was unaffected when receptor internalization was blocked by pretreatment with concanavalin A or incubation at 4 degrees C, and no changes in AT1A receptor affinity or number were observed. Receptor desensitization was also unaffected by inhibition or activation of protein kinase C. Thus, we have established a permanent, high-level transfectant of the AT1A receptor in CHO-K1 cells and have shown that these receptors rapidly desensitize following exposure to physiological concentrations of agonist. The mechanism of rapid desensitization is not related to receptor sequestration, internalization or controlled by PKC phosphorylation. This provides an excellent model for studying AII actions mediated through a specific receptor subtype, at subnanomolar concentrations.
Mol Cell Biochem 1995 May 10
PMID:Stable expression of a functional rat angiotensin II (AT1A) receptor in CHO-K1 cells: rapid desensitization by angiotensin II. 765 82

We previously reported that angiotensin II (Ang II) increases cGMP content through a new Ang II receptor subtype that is distinct from both the AT1 and AT2 subtypes in differentiated Neuro-2A cells. In this study, the mechanism of the Ang II-stimulated cGMP increase was investigated in comparison with bradykinin- and atrial natriuretic factor (ANF)-stimulated cGMP increases in differentiated Neuro-2A cells. Ang II increased cGMP in differentiated Neuro-2A cells rapidly, with a maximal effect in 30 sec and a return to basal levels in 60 sec. Removal of extracellular Ca2+ or pretreatment with a membrane-permeable Ca2+ chelator [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester] attenuated Ang II-stimulated cGMP accumulation. Both the time course and Ca2+ dependency of the effect of Ang II were similar to those of the effect of bradykinin, which activates soluble guanylyl cyclase, but distinct from those of the effect of ANF, which activates particulate guanylyl cyclase. Methylene blue, an inhibitor of soluble guanylyl cyclase, attenuated the effects of Ang II and bradykinin but not that of ANF. LaCl3, a nonspecific Ca2+ blocker, prevented Ang II-stimulated cGMP accumulation. L-type Ca2+ channel blockers, nifedipine and diltiazem, or an N-type Ca2+ channel blocker, omega-conotoxin, failed to inhibit the effect of Ang II. Ang II had no effect on formation of 1,4,5-inositol trisphosphate or cAMP content, whereas bradykinin stimulated 1,4,5-inositol trisphosphate formation in differentiated Neuro-2A cells. Further, the nitric oxide synthase inhibitors NG-monomethyl-L-arginine and NG-nitro-L-arginine attenuated Ang II- and bradykinin-stimulated elevation of cGMP content but not that stimulated by ANF. The Ca2+ ionophore A23187 also stimulated cGMP formation and the effect was inhibited by the nitric oxide synthase inhibitors. These results indicate that the newly found Ang II receptor mediates cGMP formation through activation of soluble guanylyl cyclase and that the activation is mediated by nitric oxide, which is increased by Ca2+ influx via an ion channel distinct from the L-type and N-type Ca2+ channels.
Mol Pharmacol 1993 Apr
PMID:New signaling mechanism of angiotensin II in neuroblastoma neuro-2A cells: activation of soluble guanylyl cyclase via nitric oxide synthesis. 768 50

The two forms of angiotensin II (Ang II) receptors, AT1 and AT2 subtypes, have been demonstrated in many other cells beside the anterior pituitary cells. Attempting to investigate the subtype(s) of Ang II receptors implicated in the multiple transduction mechanisms involved in Ang II stimulation of prolactin (PRL) release by lactotropes, we studied the effect of selective nonpeptidergic Ang II antagonists on the PRL release, adenylate cyclase (AC), and phospholipase C activities. In intact cells, the AT1 antagonist DuP753 blocked Ang II-induced PRL release, reversed in a dose dependent manner Ang II-evoked inositol phosphates production, and inhibited completely the PLC and protein kinase C (PKC) dependent cAMP accumulation induced by Ang II. In membrane preparations, the Ang II receptors were negatively coupled to AC. The AT1 antagonist blocked in a dose dependent manner the inhibitory effect of Ang II on cAMP production. In intact cells, the negative coupling of Ang II receptor with AC was observed only when PKC was down regulated by long term 12-O-tetradecanolylphorbol-13-acetate pretreatment. Ang II was able to inhibit vasoactive intestinal peptide-induced cAMP accumulation, a response which was also prevented by DuP753. The different coupling of Ang II receptor described above implicated only the AT1 type receptor since the AT2 antagonists (PD123177 and PD123319) were ineffective at any doses tested (10(-8) to 10(-5) M). The obtained results indicate that the regulation of PRL secretion involves the AT1 receptor subtype and that this receptor might be coupled to multiple effectors.
Mol Cell Neurosci 1994 Dec
PMID:Angiotensin II effects on second messengers involved in prolactin secretion are mediated by AT1 receptor in anterior pituitary cells. 770 34

Alveolar epithelial type II (AT2) cells have been thought to be the progenitors of terminally differentiated type I (AT1) cells in the adult animal in vivo. In this study, we used an AT1 cell-specific monoclonal antibody (mAb VIII B2) to investigate expression of the AT1 cell phenotype accompanying reversible changes in expression of the AT2 cell phenotype. AT2 cells were isolated and cultured either on attached collagen gels or on gels detached 1 or 4 days after plating and maintained thereafter as floating gels. Monolayers on both attached and floating gels were harvested on days 4 and 8 and analyzed by electron microscopy for changes in morphology and binding of mAb VIII B2. Results indicate that: (1) alveolar epithelial cells (AEC) on attached gels develop characteristics of the AT1 cell phenotype, (2) AEC on gels detached on day 1 maintain features of the AT2 cell phenotype (and do not react with mAb VIII B2), and (3) the expression of AT1 cell phenotypic traits seen by day 4 on attached gels is reversed after detachment. We conclude that commitment to the AT1 and AT2 cell lineages requires continuous regulatory input to maintain the differentiated states, and that transdifferentiation between AT2 and AT1 cells may be reversible.
Am J Respir Cell Mol Biol 1995 May
PMID:Reversible transdifferentiation of alveolar epithelial cells. 774 13

Angiotensin II (Ang II) is an essential component of the renin-angiotensin system and is partially responsible for the maintenance of hypertension. Two major receptor subtypes have been defined for Ang II and have been detected in the heart of various species. Most of the known functions of Ang II are mediated via the AT1 subtype, whereas the function of the AT2 receptor remains ill defined. In this study we aimed to localize both receptor subtypes in the rabbit heart using film and light microscope autoradiography as well as radioligand binding assays on membranes. Total receptor densities in the atrium and nervous tissue were respectively four and nine times greater than in the ventricle. Conductive tissue shows a density between that of atrial and nervous tissue. In the ventricle, approximately 20% of the Ang II receptors were AT2. This receptor subtype was almost totally absent from nervous, conductive and atrial tissue. The limited resolution of the microscope autoradiography method did not allow us to specify the exact cell-type at this stage.
J Mol Cell Cardiol 1995 Jan
PMID:Localization of angiotensin II receptor subtypes in the rabbit heart. 776 Mar 66

Pig coronary artery rings denuded of endothelium contract to the vasoactive hormone angiotensin II (Ang II). The nature of Ang II receptors and their Ca(2+)-pool utilization were examined for contraction of the artery rings and for increase in ultracellular [Ca2+] ([Ca2+]i) in smooth muscle cells cultured from them. Ang II contracted the arteries (EC50 = 7 +/- 4 nM) but with a lower maximal force (1.4 +/- 0.25 N/g tissue) than the contraction with 60 mM K+ (6.11 +/- 0.63 N/g tissue). In the cultured cells it caused a transient increase in [Ca2+]i with an EC50 value of 11 +/- 4 nM. The cells bound Ang II with a dissociation constant (Kd) of 7 +/- 2 nM. Based on the effects of the Ang II antagonists saralasin, DuPont 753, dithiothreitol and PD123319, the Ang II receptors responsible for contraction, increase in [Ca2+]i and Ang II binding to coronary artery smooth muscle were of type AT1. The contraction to Ang II was abolished by EGTA but not by nitrendipine. The sarcoplasmic Ca2+ pump inhibitors cyclopiazonic acid (10 microM CPA) and thapsigargin (1 microM) produced contractions of 4.35 +/- 0.73 and 2.07 +/- 0.54 N/g, respectively. Ang II contractions in the control arteries were nearly abolished upon pretreatment with CPA and thapsigargin. CPA and thapsigargin induced contractions were abolished by exposure to EGTA for 1 h but short exposure of the cells to EGTA only modulated the CPA or thapsigargin induced increase in [Ca2+]i; Ang II induced increase in [Ca2+]i was not inhibited by 1 microM nitrendipine but was reduced significantly by a 30-60 sec exposure to EGTA.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Biochem 1994 Jun 15
PMID:Angiotensin II contractions in coronary artery. Nature of receptors and calcium pools. 781 52

A systematic search has been used to derive a hypothesis for the receptor-bound conformation of A-II antagonists at the AT1 receptor. The validity of the pharmacophore hypothesis has been tested using CoMFA, which included 50 diverse A-II antagonists, spanning four orders of magnitude in activity. The resulting cross-validated R2 of 0.64 (conventional R2 of 0.76) is indicative of a good predictive model of activity, and has been used to estimate potency for a variety of non-peptidyl antagonists. The structural model for the non-peptide has been compared with respect to the natural substrate, A-II, by generating peptide to non-peptide overlays.
J Comput Aided Mol Des 1994 Oct
PMID:Derivation of a 3D pharmacophore model for the angiotensin-II site one receptor. 787 97

Cells from patients with ataxia-telangiectasia (AT) are more sensitive than cells from normal individuals to a number of compounds which induce DNA damage via oxygen-derived free radical attack. We tested the hypothesis that AT cells would show a sensitivity to reactive oxygen species (ROS) generated by activated inflammatory cells. AT cells were exposed to neutrophils activated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or to xanthine/xanthine oxidase (X/XO), an enzyme system which generates superoxide and hydrogen peroxide. Induced micronuclei (MN) frequencies (corrected for spontaneous MN frequencies) were significantly higher in AT cell cultures than in cultures from normal individuals (comparison of MN frequencies of AT vs. normal cultures: for treatment with activated neutrophils, P = 0.003; for X/XO, P = 0.05). The comet assay was used to determine whether the elevated chromosomal damage in the treated AT cells was due to a difference in strand breakage or its rejoining. X/XO treatment was used in studies of single-stranded (SS) DNA breakage, and X-ray treatment for double-stranded (DS) DNA damage. AT and normal cells showed no significant differences in the initial levels of SS (P = 0.29) or DS (P = 0.91) DNA damage. Likewise, they exhibited similar rejoining kinetics (rejoining half-time for SS = 10 min, for DS = 30 min). These data support the involvement of the AT loci in determining a cell's ability to deal with oxidative stress, although the mechanism underlying this effect has yet to be resolved. The data also suggest that AT patients are at elevated risk of sustaining DNA damage in tissues undergoing inflammatory reactions.
Environ Mol Mutagen 1994
PMID:Response of fibroblast cultures from ataxia-telangiectasia patients to reactive oxygen species generated during inflammatory reactions. 792 23

1. Intracerebral injection of the oxidative metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenylpyridine (MPP+), into the substantia nigra of adult rats resulted in a lesion at the injection site. 2. Using autoradiography, we localized specific [125I]CGP 42112 binding that was not recognized by angiotensin II or angiotensin II AT1 or AT2 receptor-selective ligands. 3. Our results suggest that [125I]CGP 42112 may be binding to activated microglia that appear at the lesion site.
Cell Mol Neurobiol 1994 Feb
PMID:[125I]CGP 42112 reveals a non-angiotensin II binding site in 1-methyl-4-phenylpyridine (MPP+)-induced brain injury. 795 64

We recently described the photoaffinity labeling and partial characterization of the angiotensin type 2 (AT2) receptor from human myometrium. In the present study, specific receptors for angiotensin II (AII) were also analyzed in a murine fibroblast cell line (R3T3) and a rat pheochromocytoma cell line (PC-12). Dose-displacement experiments with PD 123319 (an AT2-selective antagonist) completely inhibited 125I-AII binding, whereas L-158,809 (an AT1-selective antagonist) had no significant effect on 125I-AII binding, thus revealing that these two cell lines express exclusively AT2 sites. High yields of covalent and selective labelling of AT2 receptors from human myometrium, R3T3 cells, and PC-12 cells were obtained with the photosensitive analogue 125I-[Sar1,Val5,p-benzoyl-Phe8]AII. Gel permeation chromatography of Triton X-100-solubilized AT2 receptors from the three different sources revealed similar Stokes' radii of about 65 A. Interestingly, upon electrophoresis under reducing conditions, marked disparities were observed between the apparent molecular masses of AT2 receptors from the three different sources. As observed previously, AT2 receptors from human myometrium showed a molecular mass of 68 +/- 4.6 kDa. AT2 receptors from PC-12 cells showed a larger molecular mass of 113 +/- 12 kDa, whereas AT2 receptors from R3T3 cells showed a molecular mass of 91 +/- 7.8 kDa. After endoglycosidase digestion with an enzyme that cleaves N-linked saccharides, the molecular masses of the denatured AT2 receptors of human myometrium, R3T3 cells, and PC-12 cells were decreased by 54%, 66%, and 73%, to 31.3 +/- 1.6 kDa, 30.9 +/- 0.7 kDa, and 30.6 +/- 0.8 kDa, respectively. Kinetic studies with AT2 receptors from human myometrium revealed a complex, multiple-step process of deglycosylation involving at least three different sites of N-linked saccharides. These results suggest that the disparity in the sizes of AT2 receptors from different sources is mostly related to different degrees of N-glycosylation. They also imply that the AT2 receptor contains at least three asparagine-linked sites of glycosylation.
Mol Pharmacol 1994 Jun
PMID:The marked disparity between the sizes of angiotensin type 2 receptors from different tissues is related to different degrees of N-glycosylation. 802 4


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