Cloning, expression, and characterization of a gene encoding the human angiotensin II type 1A receptor

Suppressive effects of type I angiotensin receptor antagonists, candesartan and irbesartan on allergic asthma

The effects of candesartan and irbesartan, antagonists of the type I angiotensin II receptor, were investigated on allergic asthma. The antigen-induced degranulation was measured by evaluating β-hexosaminidase activity in vitro. Additionally, a murine ovalbumin-induced allergic asthma model was used to test the in vivo efficacy. It was observed that while candesartan inhibited the antigen-induced degranulation in rat RBL-2H3 mast cells, irbesartan did not. Administration of candesartan and irbesartan decreased the number of immune cells in the bronchoalveolar lavage fluid and reduced the expression of Th2 (IL-4, IL-5, and IL-13) and Th1 cytokines (IL-2 and IFN-γ) in the lung tissues of mice with ovalbumin-induced allergic asthma. Histological studies revealed that both antagonists reduced inflammation and mucin production in the lungs. Therefore, these findings provide evidence that candesartan and irbesartan could have potential applications as anti-allergic agents.

Identification of isobavachalcone as a potential drug for rice blast disease caused by the fungus Magnaporthe grisea

The rice blast disease caused by the fungus Magnaporthe grisea is one of the most devastating rice diseases, but there is no effective fungicide toward chitinase which is a key enzyme of M. grisea. In this study, we observed that distortion and cell-wall damage of M. grisea hyphae were significantly under the scanning electron micrograph after a 24-h treatment with 10 mg/L isobavachalcone (IBC) extracted from Psoralea corylifolia L. To further explore the effect of IBC on the cell wall of M. grisea, we examined changes in enzymes associated with cell wall degradation by enzyme activity experiments, treated liquid culture mycelia with 10 mg/L IBC for 1 h. Results displayed that chitinase was obviously more active than control group. To illustrate the interactions between IBC and chitinase, the studies of homology modeling and molecular docking were carried out successively. The results revealed that IBC had hydrogen bonds with residues ASP267 and ARG276 of chitinase. Besides, these nonpolar residues TYR270, PRO271, VAL272, LEU310, PRO311, TYR316, and LEU317 were able to form strong hydrophobic interactions. Binding energies of the chitinase-IBC complexes were calculated by MM-GBSA showed that the ΔG_bind score of molecular dynamics had lower binding energy and more stable than docking complexes. All above, IBC owns significant agonistic activity in chitinase and would be a potent fungicide to inhibit the growth of M. grisea. We hope the above information provides an important insight for understanding the interactions between IBC and chitinase, which may be useful in the discovery of a novel potent agonist. Communicated by Ramaswamy H. Sarma.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

Agonistic autoantibodies against the angiotensin AT1 receptor increase in unstable angina patients after stent implantation

OBJECTIVES

Agonistic AT1 receptor autoantibodies have been described in patients with hypertension and preeclampsia. These autoantibodies could stimulate proliferation of vascular smooth muscle cells (VSMCs), which are involved in angiotensin II-induced vascular injury in cardiovascular disease. Hence, in this study, we explored the existence of agonistic AT1 receptor autoantibodies in unstable angina (UA) patients and the possible effects of them on the in-stent restenosis of these patients.

METHODS

A total of 95 UA patients and 98 healthy volunteers were enrolled. The serum of each patient was analyzed for the presence of AT1 receptor autoantibodies by enzyme-linked immunosorbent assay. Their effects on VSMC proliferation and c-fos and c-jun expression were studied in vitro.

RESULTS

AT1 receptor autoantibodies were detected in 34/95 patients with UA. The incidence was 10.2% in the control group and rose to 47.37% after stent implantation. In vitro, this autoantibody had agonist-like activity, shown as stimulation of VSMC proliferation and upregulation of c-fos and c-jun expression. These effects were similar to that of angiotensin II and could be weakened partly by the AT1-receptor blocker valsartan.

CONCLUSION

Our findings show that the autoantibody from UA patients has similar agonistic activity to angiotensin II and might play a role in the pathogenesis of in-stent restenosis in these patients.

IMPORTANCE OF THE ANGIOTENSIN TYPE 1 RECEPTOR IN ANGIOTENSIN II–INDUCED BRONCHOCONSTRICTION AND BRONCHIAL HYPERRESPONSIVENESS IN THE GUINEA PIG

Although angiotensin II (Ang II) causes bronchoconstriction and bronchial hyperresponsiveness to methacholine in mildly asthmatic patients, the responsible mechanisms for these reactions are unclear. The authors examined the effect of intravenous infusion of Ang II on airway constriction in guinea pigs. Furthermore, the effects of subthreshold concentrations of Ang II on bronchial responsiveness to methacholine were investigated. Airway opening pressure (Pao), an index of bronchoconstriction, increased dose dependently after intravenous infusion of 3 and 10 nmol/kg Ang II (72.2 and 236.5 increase above the baseline value, respectively). In another set of experiments, animals received a methacholine inhalation challenge under a constant intravenous infusion of a subthreshold dose of Ang II (2 nmol/kg/min). The Ang II infusion elicited bronchial hyperresponsiveness to methacholine. The provocative concentration of methacholine, which produced a 200% increase above the baseline Pao (PC200), decreased from 306.9 to 156.1 micrograms/mL upon Ang II infusion. Pretreatment with TCV-116, a type 1 Ang II (AT1) receptor antagonist, but not PD123319, a type 2 Ang II (AT2) receptor antagonist, dose dependently prevented both the Ang II-induced bronchoconstriction and bronchial hyperresponsiveness to methacholine. The authors conclude that Ang II caused bronchoconstriction and induced bronchial hyperresponsiveness to methacholine via the AT1 receptors and that this effect did not involve the release of other bronchoactive mediators.

Effect of candesartan, a type 1 angiotensin II receptor antagonist, on bronchial hyper-responsiveness to methacholine in patients with bronchial asthma

AIMS

Angiotensin II is a putative mediator in bronchial asthma. There have been very few studies investigating the involvement of angiotensin II receptors in bronchial hyper-responsiveness in asthmatic patients. We examined the effect of candesartan cilexetil, a specific angiotensin II type 1 (AT1) receptor antagonist, on bronchial responsiveness to inhaled methacholine in patients with asthma.

METHODS

Bronchial responsiveness to methacholine, assessed as the concentration of methacholine producing a 20% fall in FEV1 (PC20-FEV1), was measured on three occasions 2 weeks apart in 11 stable asthmatic patients. Candesartan cilexetil (8 mg once a day) or a placebo was orally administered for 1 week before the methacholine provocation test in a double-blind, randomized, crossover manner.

RESULTS

Although there were no significant differences between treatment periods in FEV1 values at baseline, the geometric mean (95% CI) PC20-FEV1 values increased significantly (P = 0.041) from 0.691 (0.379, 1.259) mg ml-1 with placebo to 0.837 (0.506, 1.384) mg ml-1 with candesartan. Candesartan decreased the mean (95% CI) arterial blood pressure (placebo: 95.6 (89.0, 102.2) mmHg, candesartan: 86.4 (79.8, 93.1) mmHg, P = 0.015). There was no correlation between the change in blood pressure and the change in PC20-FEV1.

CONCLUSIONS

We conclude that AT1 receptors are involved in bronchial hyper-responsiveness in asthmatic patients.

Altered signal pathway in angiotensin II-stimulated neutrophils of patients with hypercholesterolaemia

Angiotensin II (AII) in 1-10 nM concentrations has an in vivo immunostimulating effect on human neutrophils. The release of superoxide anions and leukotrienes (LTs) is significantly increased by 10 nM AII-stimulated neutrophils of patients with hypercholesterolaemia (HCH). These oxidizing agents may be involved in the damage of vessel walls, i.e., in atherosclerotic plaque formation. To clarify the receptor types and signal pathways in neutrophils of healthy controls and patients, inositol trisphosphate (IP(3)) production and Ca(2+) signalling were studied. Neutrophils were pretreated before AII stimulation with different inhibitory drugs. In control cells, the stimulation occurred predominantly through pertussis toxin-sensitive, type angiotensin 1 receptors. This induced IP(3) production and Ca(2+) signalling from intracellular pools. In neutrophils of hypercholesterolaemic patients, the enhanced release of oxidizing agents was dependent more on type angiotensin 2 than type angiotensin 1 receptors. After stimulation, there was no IP(3) production detected. The Ca(2+) signalling was lower than in control cells and was dependent on extracellular Ca(2+).

The angiotensin II type 1 receptor and receptor-associated proteins

The mechanisms of regulation, activation and signal transduction of the angiotensin II (Ang II) type 1 (AT1) receptor have been studied extensively in the decade after its cloning. The AT1 receptor is a major component of the renin-angiotensin system (RAS). It mediates the classical biological actions of Ang II. Among the structures required for regulation and activation of the receptor, its carboxyl-terminal region plays crucial roles in receptor internalization, desensitization and phosphorylation. The mechanisms involved in heterotrimeric G-protein coupling to the receptor, activation of the downstream signaling pathway by G proteins and the Ang II signal transduction pathways leading to specific cellular responses are discussed. In addition, recent work on the identification and characterization of novel proteins associated with carboxyl-terminus of the AT1 receptor is presented. These novel proteins will advance our understanding of how the receptor is internalized and recycled as they provide molecular mechanisms for the activation and regulation of G-protein-coupled receptors.

A cDNA from human bone marrow encoding a protein exhibiting homology to the ATP1gamma1/PLM/MAT8 family of transmembrane proteins

A cDNA clone, IWU-1, was cloned from human bone marrow. Its putative open reading frame encoded a protein of 115 amino acids with a calculated molecular mass of 12.9 kDa. The deduced amino acid sequence exhibited high homology (>68%) to members of the ATP1gamma1/PLM/MAT8 family of single transmembrane proteins, primarily in the region containing the putative transmembrane domain. The sequence at the amino-terminal side exhibited high homology (>61%) to the cytoplasmic region of the angiotensin II type 1 receptors.

Effect of losartan, a type 1 angiotensin II receptor antagonist, on bronchial hyperresponsiveness to methacholine in patients with bronchial asthma

It is unclear whether angiotensin II receptors are involved in bronchial hyperresponsiveness in asthmatic patients. We examined the effect of losartan, a specific angiotensin II type 1 (AT1) receptor antagonist, on bronchial responsiveness to inhaled methacholine in eight patients with stable asthma. Bronchial responsiveness to methacholine, assessed as the concentration of methacholine producing a 20% fall in FEV(1) (PC(20)-FEV(1)) and a 35% fall in standardized partial expiratory flow at 40% of FVC (PC(35)-PEF(40)), was measured on two occasions 2 wk apart. Losartan (50 mg once a day) or a placebo was orally administered for 1 wk before methacholine provocation test in a double-blind, randomized, crossover fashion. Although the PC(20)-FEV(1) values after placebo (2.037 [geometric standard error of the mean, GSEM = 0.210] mg/ml) and losartan (2.098 [GSEM, 0.239] mg/ml) were identical (p = 0.840), the geometric mean PC(35)-PEF(40) values significantly (p = 0.034) increased from 0.258 (GSEM, 0.156) mg/ml with placebo to 0.456 (GSEM, 0.186) mg/ml with losartan. We conclude that AT1 receptors are involved in bronchial hyperresponsiveness in asthmatic patients. This is the first report demonstrating the involvement of AT1 receptors in bronchial asthma.

Type 1 angiotensin II receptor antagonism reduces antigen-induced airway reactions

Although the renin-angiotensin system is activated in patients with asthma during severe acute attacks and angiotensin II has been shown to cause bronchoconstriction in patients with asthma, the role of angiotensin II in patients with asthma is unclear. We investigated the effects of two specific antagonists at type 1 and type 2 angiotensin II receptors, candesartan cilexetil (TCV-116) and PD123319, on antigen-induced airway reactions in guinea pigs. Sixty minutes after intraperitoneal administration of candesartan cilexetil (0.1, 1.0, or 10 mg/kg) or PD123319 (30 mg/kg), animals received an antigen challenge. Airway responsiveness to inhaled methacholine was assessed as the dose of methacholine required to produce a 200% increase in the pressure at the airway opening (PC(200)). Differential cell counts in bronchoalveolar lavage fluids (BALF) were measured 24 h after antigen challenge. Candesartan cilexetil did not inhibit antigen-induced bronchoconstriction in sensitized guinea pigs or alter PC(200) in nonsensitized guinea pigs. Antigen inhalation significantly increased bronchoconstrictor responses to methacholine and increased airway accumulation of eosinophils; both responses showed dose-dependent prevention by candesartan but not by PD123319. These results indicate that endogenous angiotensin II promotes antigen-induced airway hyperresponsiveness and eosinophil accumulation by acting at type 1 receptors.

Role of the His273 located in the sixth transmembrane domain of the angiotensin II receptor subtype AT2 in ligand-receptor interaction

Angiotensin II receptor subtypes AT1 and AT2 are proteins with seven transmembrane domain (TMD) topology and share 34% homology. It was shown that His256, located in the sixth TMD of the AT1 receptor, is needed for the agonist activation by the Phe8 side chain of angiotensin II, although replacing this residue with arginine or glutamine did not significantly alter the affinity binding of the receptor. We hypothesized that the His273 located in the sixth transmembrane domain of the AT2 receptor may play a similar role in the functions of the AT2 receptor, although this residue was not identified as a conserved residue in the initial homology comparisions. Therefore, we replaced His273 of the AT2 receptor with arginine or glutamine and analyzed the ligand-binding properties of the mutant receptors using Xenopus oocytes as an expression system. Our results suggested that the AT2 receptor mutants His273Arg and His273 Glu have lost their affinity to [125I-Sar1-Ile8]Ang II, a peptidic ligand that binds both the AT1 and AT2 receptors and to 125I-CGP42112A, a peptidic ligand that binds specifically to the AT2 receptor. Thus, His273 located in the sixth TMD of the AT2 receptor seems to play an important role in determining the binding properties of this receptor. Moreover, these results along with our previous observation that the Lys215 located in the 5th TMD of the AT2 receptor is essential for its high affinity binding to [125I-Sar1-Ile8]Ang II indicate that key amino acids located in the 5th and 6th TMDs of the AT2 receptor are needed for high affinity binding of the AT2 to its ligands.

Role of the third intracellular loop of the angiotensin II receptor subtype AT2 in ligand-receptor interaction

Angiotensin II (Ang II) receptor subtypes AT1 and AT2 share 34% overall homology, but the least homology is in their third intracellular loop (3rd ICL). In an attempt to elucidate the role of the 3rd ICL in determining the similarities and differences in the functions of the AT1 and the AT2 receptors, we generated a chimeric receptor in which the 3rd ICL of the AT2 receptor was replaced with that of the AT1 receptor. Ligand-binding properties and signaling properties of this receptor were assayed by expressing this receptor in Xenopus oocytes. Ligand-binding studies using [125I-Sar1-Ile8] Ang II, a peptidic ligand that binds both the AT1 and the AT2 receptor subtypes, and 125I-CGP42112A, a peptidic ligand that is specific for the AT2 receptor, showed that the chimeric receptor has lost affinity to both ligands. However, IP3 levels of the oocytes expressing the chimeric receptor were comparable to the IP3 levels of the oocytes expressing the AT1 receptor, suggesting that the chimeric receptors could couple to phospholipase C pathway in response to Ang II. We have shown previously that the nature of the amino acid present in the position 215 located in the fifth transmembrane domain (TMD) of the AT2 receptor plays an important role in determining its affinity to different ligands. Our results from the ligand-binding studies of the chimeric receptor further support the idea that the structural organization of the region spanning the 5th TMD and the 3rd ICL of the AT2 receptor has an important role in determining the ligand-binding properties of this receptor.

Human spiral artery renin-angiotensin system

Pregnancy induces uterine spiral arteries to remodel into dilated uteroplacental vessels by an unknown mechanism called "physiological change." In women who develop preeclampsia, however, many spiral arteries remain unchanged or develop medial hyperplasia and atherosis. We recently demonstrated that angiotensinogen is expressed by remodeling spiral arteries in first-trimester decidua. We hypothesize that a local spiral artery renin-angiotensin system mediates pregnancy-induced remodeling of these vessels. In this study we tested for expression of renin, angiotensin-converting enzyme, and angiotensin II type 1 receptor genes in the first-trimester uterus using reverse-transcription polymerase chain reaction. Expression was localized by in situ hybridization and immunohistochemistry. Renin, angiotensin-converting enzyme, and the angiotensin II type 1 receptor are all expressed in and around remodeling spiral arteries. These observations suggest that a local spiral artery renin-angiotensin system may play a role in pregnancy-induced remodeling of these vessels. Elevated angiotensinogen expression in women homozygous for the A(-6) variant in the angiotensinogen promoter may promote abnormal remodeling, whereas relatively lower levels in women homozygous for G(-6) may permit enough normal remodeling to protect these women from preeclampsia.

Nonpeptide angiotensin II receptor antagonist recognizes inter-species differences in angiotensin AT1 receptors

Oral administration of the angiotensin AT1 receptor antagonist 3-methyl-2,6-dimethyl-4-[[2'-(1H-tetrazol-5-yl)-1,1'-biphenyl-4-yl ]methoxy] pyridine (ME3221) inhibited the pressor response to angiotensin II at doses of 0.3-1.0 mg/kg in rats. A higher dose of ME3221 (3-10 mg/kg) was required to obtain the same inhibitory potency in dogs. The antagonistic potency of ME3221 for angiotensin II-induced contraction in the rabbit aorta (pA2 = 8.82) was about five times higher than that in the canine aorta (pA2 = 8.18). The inhibition constant of ME3221 for displacing [125I]angiotensin II binding to membrane fractions from the rabbit aorta (Ki = 3.84 nM) and rat liver (Ki = 2.55 nM) was significantly lower than that for the canine aorta (Ki = 84.5 nM), canine liver (Ki = 122 nM) and bovine adrenal cortex (Ki = 21.5 nM). In contrast, [Sar1, Ala8]angiotensin II had a similar inhibition constant (Ki = 0.85-4.67 nM) in the species investigated. Treatment with 5 mM dithiothreitol significantly (P < 0.01) reduced the angiotensin II-induced contractile response to 1.2% in the rabbit aorta, but it did not significantly reduce the response in the canine aorta (83.2%). Dithiothreitol reduced [125I]angiotensin II binding to membrane fractions from the rabbit aorta and the rat liver but partially inhibited binding in preparations that had a low affinity for ME3221. These data indicate a species difference in the angiotensin AT1 receptor: the canine and bovine angiotensin AT1 receptor has a relatively low affinity for ME3221 and is slightly resistant to dithiothreitol. The species difference in the angiotensin AT1 receptor reflects the in vivo efficacy of ME3221 in rats and dogs.

Mutational analysis of the angiotensin II type 2 receptor: contribution of conserved extracellular amino acids

While much work has been done examining the ligand-binding characteristics of the AT1 receptor, very little attention has been focused on the AT2 receptor. Both receptors bind angiotensin II (AngII) with identical affinities, but share only 34% homology. Although it is tempting to assume that conserved residues between the two subtypes are responsible for the binding of AngII, there is little data to support this view. To determine the commonalities in ligand binding of the AT1 and AT2 receptors, we have chosen several conserved extracellular amino acids which have been shown to be important in AngII binding [1,2] to the AT1 receptor for mutational studies of the AT2 receptor. Specifically, we have mutated tyrosine108 in extracellular loop 1 (ECL1), arginine182 in ECL2, and aspartate297 in ECL3 of the AT2 receptor in order to determine their contribution to AngII binding. In the AT2 receptor, mutation of tyrosine108 to an alanine resulted in a receptor with wild-type binding for AngII, while mutation of either arginine182 or aspartate297 drastically impaired AngII binding ( > 100 nM). These results demonstrate both similarities as well as clear differences between receptor subtypes in the contributions to AngII binding of several conserved extracellular amino acid residues.

A novel putative G-protein-coupled receptor expressed in lung, heart and lymphoid tissue

cDNA encoding a novel putative G-protein-coupled receptor, named LyGPR (lymphocyte derived G-protein-coupled receptor) was cloned using a reverse transcription-PCR approach. The LyGPR amino acid sequence is 375 residues long and shows similarity (about 30-35% identity) both to the angiotensin receptors and members of the chemokine receptor family. Northern blot analysis revealed a 3.1-kb LyGPR transcript expressed predominantly in lung, heart and lymphoid tissues. LyGPR expression was also detected in the pre-B acute lymphoblastoid leukemia cell lines Reh and Nalm-6, in the Burkitt's lymphoma line Daudi, and in hematopoietic progenitor cells from bone marrow, as well as in B cells, T cells and monocytes from peripheral blood.

The unpredicted high affinities of a large number of naturally occurring tachykinins for chimeric NK1/NK3 receptors suggest a role for an inhibitory domain in determining receptor specificity

Three chimeric receptors were constructed by exchanging exon sequences between human NK1 and NK3 receptor genes. The resulting chimeric receptors not only retained high affinities for their natural ligands substance P and neurokinin B but also exhibited surprisingly high affinities for other naturally occurring tachykinins including neurokinin A, neuropeptide K, neuropeptide gamma, eledoisin, kassinin, physalaemin, and phyllomedusin. In contrast, these chimeric receptors displayed a wide range of variability in their affinities for non-naturally occurring ligands including selective agonists and antagonists of NK1, NK2, and NK3 receptors. Since the only common feature among these naturally occurring neurokinin peptides is the conserved C-terminal sequences, our data suggest that these conserved sequences must play the major role in conferring high affinity binding to the chimeric receptors. To explain the apparently "improved" affinities of these naturally occurring ligands for the chimeric receptors as compared with their affinities for the parent NK1 and NK3 receptors, we are proposing that certain inhibitory domains that are present in the NK1 and/or NK3 receptors are compromised in these chimeric receptors. Upon disruption of these inhibitory domains during the formation of chimeras, the naturally occurring ligands can interact more favorably with chimeric receptors through their conserved C-terminal sequences. Based on this hypothesis, the binding affinities of natural tachykinin ligands may be largely determined by their conserved C-terminal sequences, whereas receptor selectivities of these ligands are influenced more by the presence or absence of inhibitory domains rather than specific binding domains on their target receptors.

Angiotensin I-converting enzyme genotypes and angiotensin II receptors. Response to therapy

In the present study, we studied angiotensin II type 1 (AT1) and type 2 (AT2) receptor messengers by quantitative reverse transcriptase-polymerase chain reaction. We examined peripheral blood mononuclear cells from 30 healthy subjects and 50 subjects with primary hypertension, in whom angiotensin I-converting enzyme genotype was determined, before and after 15 days of treatment with different antihypertensive drugs. The medication included a calcium channel antagonist, an angiotensin I-converting enzyme inhibitor, and a beta 1-blocker. We also studied the relationship between AT1 receptor gene expression and biochemical parameters of the renin-angiotensin system. AT1 receptor messenger levels were positively correlated with plasma renin activity in both normotensive and untreated hypertensive subjects. Increases of this messenger and plasma angiotensin II levels were correlated with the D allele in the same individuals. AT1 receptor messenger levels decreased significantly with angiotensin I-converting enzyme inhibitor treatment in subjects with the DD genotype, and a significant decrease was observed in subjects with the II and ID genotypes treated with a calcium antagonist. No changes were observed in mRNA with the beta 1-blocker. We conclude that the AT2 receptor is not expressed in peripheral leukocytes and that AT1 receptor messenger levels vary in relation to angiotensin I-converting enzyme genotype and pharmacological treatment. These results suggest that angiotensin I-converting enzyme genotype may be an important factor when deciding on antihypertensive therapy in individuals with primary hypertension.

Na+ transport by human placental brush border membranes: are there several mechanisms?

Na+ transport was evaluated in brush border membrane vesicles isolated from the human placental villous tissue. Na+ uptake was assayed by the rapid filtration technique in the presence and the absence of an uphill pH gradient. Amiloride strongly decreased Na+ uptake whether a pH gradient was present or not. In pH gradient conditions (pH 7.5 in and 9.0 out), 1 mM amiloride decreased the 10 mM Na+ uptake by 84%. In the absence of pH gradient (pH 7.5 in and out), Na+ uptake was lower but still sensitive to amiloride. The Lineweaver-Burk plot of Na+ uptake consistently showed a single kinetics. Increasing the pH gradient decreased Km values of the amiloride-sensitive Na+ uptake, leaving the Vmax unchanged. In the absence of a pH gradient, the amiloride sensitive Na+ transport was maximal at pH 7.5. Here again, a single kinetics was observed, and pH influenced exclusively the Km of Na+. Since ethylisopropylamiloride, the specific Na/H exchanger inhibitor mimicked the effects of amiloride, decreasing by 98% the 10 mM Na+ uptake, whereas benzamil, the Na+ channel blocker, had no effect, it was concluded that the amiloride sensitive Na+ uptake was predominantly or exclusively due to a Na+-H+ exchanger activity. K+ in trans-position significantly decreased the amiloride sensitive uptake. In contrast, the presence of the cation in cis-position had no effect. The amiloride resistant Na+ transport was neither influenced by pH, nor saturable. Incubation of the placental tissue with 100 microM or 1 mM dibutyryl cAMP, 0.1 or 1 microM phorbol myristate acetate, 10(-7) M insulin, 10(-10) M angiotensin II, or 10(-8) M human parathyroid hormone (PTH) did not influence Na+ transport by subsequently prepared brush border membranes. Finally, we failed to demonstrate any Na+-H+ exchange activity in the basal plasma membrane. These results indicate that (1) in the absence of cosubstrates such as phosphate and aminoacids, the Na+-H+ exchange is probably the unique mechanism of Na+ transport by the placental brush border membrane, (2) the placental isoform of the exchanger is not regulated by PTH, angiotensin, nor insulin and, therefore, is different from the isoform present in the renal brush border membrane, and (3) there is no exchanger activity in the basal plasma membrane.

The ligand binding site of the angiotensin AT1 receptor

The angiotensin AT1 receptor mediates numerous physiological actions of the octapeptide hormone, angiotensin II, in its cardiovascular and other target tissues. The binding of angiotensin II to the AT1 receptor is dependent on both intramembrane and extracellular regions of the receptor molecule. Non-peptide antagonists that block angiotensin binding and action interact exclusively with residues located within the intramembrane binding pocket of the AT1 receptor. However, peptide ligands also interact with extracellular residues to form additional bonds that stabilize their binding to the receptor. Here, László Hunyady, Tamás Balla and Kevin Catt describe how these and other studies have shown that interaction of ligands with residues in the intramembrane binding pocket is the conserved mechanism required for agonist activation of G protein-coupled receptors.

Comparative expression of vasopressin and angiotensin type-1 receptor mRNA in rat hypothalamic nuclei: a double in situ hybridization study

Angiotensin II (Ang) injected intracerebroventricularly stimulates neurohypophyseal vasopressin (AVP) release into the peripheral circulation. As we have shown previously, central actions of Ang II in the rat forebrain are mediated by the AT1A receptor subtype. In the present paper, we attempted to clarify the cellular localization of the AT1A receptor mRNA in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, in order to reappraise the conflicting data on the nature of the angiotensin II receptor involved in Ang induced vasopressin release. For this purpose, double in situ hybridization was performed using a radioactive AT1A receptor riboprobe and a digoxygenin labeled AVP oligoprobe, and immunohistochemical localization of the glial marker glial fibrillary acidic protein (GFAP) on the same brain slice. The results show neuronal expression of AT1A receptor mRNA mainly in dorsal and medial parvocellular parts of the PVN, its localization in some magnocellular PVN neurons and the absence of its expression in AVP producing neurons either in the PVN or in the SON. Thus, while indirect evidence indicates the involvement of the AT1A receptor subtype in the regulation of CRH and oxytocin release, the stimulation of vasopressinergic neurons is likely due to indirect mechanisms, or to a yet unknown type of angiotensin receptor.

Binding of valsartan to mammalian angiotensin AT1 receptors

The binding characteristics of the angiotensin AT1 receptor antagonist valsartan were investigated in different animal species and tissues. Using [125I](Sar1,Ile8) angiotensin II as radioligand, affinity constants were determined in liver and adrenal rat and marmoset, human adrenal and in rat aortic smooth muscle cells. In all tissues tested, valsartan had a greater affinity for the AT1 receptor than losartan (on average 5-fold). The affinities of both antagonists were up to 30 times weaker in the dog tissues [3H]Valsartan bound with high affinity (Kd 1.44 nmol/l) to the rat aortic smooth muscle cell AT1 receptor. Binding was saturable and reversible. Non-specific binding was low (10%). Reports that [3H]losartan binds to a non-angiotensin II binding site in rat liver and in other tissues could be confirmed. [3H]Valsartan on the other hand bound only to the AT1 receptor. Using a competition binding assay with [3H]losartan on rat liver membranes it could be shown that valsartan can bind to the 'losartan binding site', but at a 10,000-fold less affinity than for the AT1 receptor. Valsartan is therefore a highly specific and selective antagonist of the AT1 receptor. Due to its high affinity and low non-specific binding it is a suitable radioactive antagonist for the study of the distribution and function of the angiotensin AT1 receptor.

Mutagenesis and the molecular modeling of the rat angiotensin II receptor (AT1)

The molecular interaction involved in the ligand binding of the rat angiotensin II receptor (AT1A) was studied by site-directed mutagenesis and receptor model building. The three-dimensional structure of AT1A was constructed on the basis of a multiple amino acid sequence alignment of seven transmembrane domain receptors and angiotensin II receptors and after the beta 2 adrenergic receptor model built on the template of the bacteriorhodopsin structure. These data indicated that there are conserved residues that are actively involved in the receptor-ligand interaction. Eleven conserved residues in AT1, His166, Arg167, Glu173, His183, Glu185, Lys199, Trp253, His256, Phe259, Thr260, and Asp263, were targeted individually for site-directed mutation to Ala. Using COS-7 cells transiently expressing these mutated receptors, we found that the binding of angiotensin II was not affected in three of the mutations in the second extracellular loop, whereas the ligand binding affinity was greatly reduced in mutants Lys199-->Ala, Trp253-->Ala, Phe259-->Ala, Asp263-->Ala, and Arg167-->Ala. These amino acid residues appeared to provide binding sites for Ang II. The molecular modeling provided useful structural information for the peptide hormone receptor AT1A. Binding of EXP985, a nonpeptide angiotensin II antagonist, was found to be involved with Arg167 but not Lys199.

Molecular evolution of receptors for eicosanoids

The amino acid sequences of the receptors for various prostaglandins, thromboxane and lipoxin, which belong to the rhodopsin family, were aligned, and a phylogenetic tree was constructed to infer the evolutionary history of the arachidonic acid cascade. The obtained tree suggested that the origin of the cyclooxygenase pathway was different from that of the lipoxygenase pathway. The receptors involved in the cyclooxygenase pathway constructed an independent cluster, but the lipoxin A4 receptor, which is involved in the lipoxygenase pathway, belonged to the cluster of peptide receptors. The primitive form of the cyclooxygenase pathway had been a signal transduction system composed of prostaglandin E2 and its receptor associated with cAMP metabolism.

Isolation of three novel human genes encoding G protein-coupled receptors

We have cloned and mapped the chromosomal location of three novel human genes encoding G protein-coupled receptors that we have named GPR6, GPR5, and GPR4. The entire coding region for each of these genes was contained on single exons. Gene GPR6 encoded a receptor that shared closest identity (71% in the transmembrane regions) with the human orphan receptor GPR3 and was localized to chromosome 6 (q21-q22.1). Northern blot analysis revealed that GPR6 transcripts were abundant in the human putamen and to a lesser extent in the frontal cortex, hippocampus, and hypothalamus. Gene GPR5 encoded a receptor that most closely resembled the orphan receptor RBS11 (48% in the transmembrane regions) and the MIP 1 alpha/RANTES receptor (45% in the transmembrane regions) and was localized to chromosome 3 (p21.3-p21.1). Gene GPR4 shared identity (40% in the transmembrane regions) with the human platelet-activating factor receptor and was localized to chromosome 19 (q13.2-q13.3).

The angiotensin type 1 and type 2 receptor families. Siblings or cousins?

The diverse actions of angiotensin II (AngII) are mediated by cell surface receptors. Molecular cloning techniques have identified two distinct subtypes of AngII receptors referred to as AT1 and AT2. It is now well accepted that multiple forms of the AT1 receptor exist, but similar diversity of the AT2 subtype has not been conclusively demonstrated. Nonetheless, several converging lines of evidence do suggest that multiple AT2 receptors may be present in brain and cultured neuron-like cells lines. For instance, some AT2 receptors are regulated by guanine nucleotides and sulfhydryl-reducing agents, whereas others are insensitive. AT2 receptor populations also exhibit differing pharmacological profiles particularly with respect to their affinity for peptidic and non-peptidic ligands. Moreover, a recently developed anti-AT2 polyclonal antisera reveals a unique pattern of immunohistochemical staining in brain and it does not immunoreact with the recently cloned AT2 receptor. Collectively, these results support the hypothesis of multiple AT2 receptors at least within the CNS. Future studies should reveal whether these putative AT2 receptor subtypes result from unique genes or cell-specific post-translational modifications of a single gene product.

Diverse factors influencing angiotensin metabolism during ACE inhibition: insights from molecular biology and genetic studies

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Characterization of the angiotensin II AT1 receptor subtype involved in DNA synthesis in cultured vascular smooth muscle cells

1. This study was undertaken in cultured vascular smooth muscle cells to characterize the angiotensin II (AII) AT1 receptor subtype involved in DNA synthesis because (i) the AII receptor involved in vascular proliferation has previously been characterized in vitro in rat aortic cells and identified as an AT1 subtype and (ii) molecular cloning and biochemical studies have provided evidence for the existence of different AT1 receptor subtypes. 2. In cultured rat aortic vascular smooth muscle (VSMC), exposure to AII (0.1 to 100 nM) resulted in a concentration-dependent increase in [3H]-thymidine incorporation with an EC50 of 1.41 +/- 0.51 nM. Maximal stimulation was observed in the presence of 100 nM AII and corresponded to 271 +/- 40% of basal [3H]-thymidine incorporation. 3. To characterize the AII AT1 receptor subtype involved in this effect, cells were exposed to AII (3 nM) in the absence or presence of increasing concentrations of various AII receptor antagonists. The stimulatory effect of AII (3 nM) on [3H]-thymidine incorporation in VSMC was antagonized by the non-selective AT1/AT2 receptor antagonist, [Sar1, Ile8]-AII (IC50 = 5.6 nM), by the AT1A/AT1B receptor antagonist, losartan (IC50 = 10.5 nM) and the AT1 receptor antagonist, L-158809 (IC50 = 0.20 nM). The selective AT2 receptor ligand, CGP 42112A, antagonized AII-induced [3H]-thymidine incorporation with an IC50 of 6.3 +/- 1.3 microM while the AT2/AT1B receptor antagonist, PD 123319, was found to be almost inactive (IC50 > 10 microM). 4. Under the same experimental conditions, angiotensin III (AIII) was found to be at least 50 times less potent than All with an apparent EC50 of 81.6 +/- 7.7 nM. At the highest concentration tested (10 microM),the effect of AIII corresponded to 327 +/- 61% of basal [3H]-thymidine incorporation.5. These results confirm that All can stimulate DNA synthesis in VSMC through an AT, receptor.Furthermore, the pharmacological characterization of this AT1 receptor is compatible with the ATlA receptor subtype recently described on cultured mesangial cells since (i) the ATIA/ATIB receptor antagonist losartan is active at nanomolar concentrations, (ii) micromolar concentrations of the AT2/AT1B receptor antagonist PD 123319 are ineffective at antagonizing the AII-induced [3H]-thymidine incorporation and (iii) All is at least 50 times more potent than AIII in stimulating DNA synthesis.

Biochemical characterization of two distinct angiotensin AT2 receptor populations in murine neuroblastoma N1E-115 cells

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.

Epidermal growth factor-enhanced human angiotensin II type 1 receptor

The human angiotensin II type 1 (AT1) receptor gene was isolated and its promoter function analyzed by deletion mutant promoter/luciferase constructs in transfected Cos 7 cells. We found that epidermal growth factor enhanced the human AT1 promoter activity twofold to threefold. The region between -227 and -366 bp from the 5' end of the cDNA was mapped for a base sequence responsive to the epidermal growth factor stimulation. By computer analysis, PEA3 transcription factor was located in this region and was shown to bind to the promoter by gel shift assay in Cos 7 and HepG2 cells. These results indicated that the human AT1 receptor enhanced by epidermal growth factor may be due to PEA3 binding to the human AT1 promoter.

Differential gene expression and regulation of angiotensin II receptor subtypes in rat cardiac fibroblasts and cardiomyocytes in culture

Although both rat cardiac nonmyocytes (mostly fibroblasts) and cardiomyocytes have a functional angiotensin II (AngII) receptor, the regulation mechanism of its subtype expression in the rat heart remains unknown. In this study, by using a binding assay and a competitive reverse-transcriptase polymerase chain reaction, we examined the regulation of AngII types 1a and 1b (AT1a-R and AT1b-R) and type 2 receptor (AT2-R) expression in embryonal day 19 (E19) and neonatal (1-d) rat cardiac fibroblasts and cardiomyocytes. The number of AT2-R in E19 fibroblasts was dramatically decreased (from 305 to 41 fmol/mg protein) in 1-d fibroblasts, whereas that of AT1-R and the mRNA levels remained unchanged. The ratio of AT1a-R to AT1b-R mRNA in both E19 and 1-d fibroblasts was 9:1. The number of AT2-R in E19 cardiomyocytes was also significantly decreased (from 178 to 87 fmol/mg protein) in 1-d cardiomyocytes, whereas the magnitude was less prominent compared with that in fibroblasts. AT1-R expression remained unaltered in E19 and 1-d cardiomyocytes. In E19 and 1-d cardiomyocytes, the AT1b-R mRNA level was 1.5-fold higher than that of AT1a-R mRNA. Dexamethasone induced significant increases in AT1a-R mRNA (2.1-fold) and numbers (1.8-fold) without changing the affinity, whereas neither AT1b-R mRNA nor the number of AT2-R was affected by dexamethasone. The AT1a-R gene transcription rate, determined by means of a nuclear run-off assay, was increased (2-fold) by dexamethasone. The half-life of AT1a-R mRNA (18 h) was unchanged by dexamethasone. These data indicate that AngII receptor subtype expression in the rat heart is regulated in a cell- and subtype-specific manner.

Characterization of a membrane glycoprotein having pharmacological and biochemical properties of an AT2 angiotensin II receptor from human myometrium

The angiotensin II receptors of human myometrial tissue were characterized using ligand binding, cross-linking with radioactive label, detergent solubilization and partial purification by lectin-affinity chromatography. Human myometrial membrane preparations contained variable amount (5-650 fmol/mg protein) of high affinity (Kd = 44-65 pM) binding sites for 125I-CGP42112, a ligand specific for the AT2 subtype of angiotensin II receptors. Competition studies with AT1-specific and AT2-specific compounds indicated that angiotensin II receptors on these membranes were exclusively of the AT2 subtype. The binding sites for 125I-CGP42112 were efficiently solubilized by the detergent Chaps, albeit with a marked decrease in affinity (Kd = 1.2 nM). The proteins in the myometrial membrane preparation were cross-linked to 125I-[Sar1, Ile8]angiotensin II (Sarile) with disuccinimidyl suberate. When low concentrations of cross-linker were used, a single radiolabelled band of about 66-70 kDa was revealed on SDS/PAGE. At higher concentrations additional bands of about 105-120 kDa and 200 kDa were labelled. The 66-70-kDa and 105-120-kDa bands were separated by electroelution of SDS/PAGE gel slices and submitted to trypsin cleavage. The tryptic-peptide maps were identical for both products, suggesting that the additional bands are homodimers and trimers of the labelled polypeptide. The Chaps-solubilized receptor was retained on wheat-germ-agglutinin-Sepharose and specifically eluted by the competing sugar triacetylchitotriose, leading to a fivefold purification factor. Treatment of the 125I-Sarile-labelled protein with N-glycanase caused a shift in its apparent molecular mass on SDS/PAGE from 66-70 kDa to 33 kDa.

Human AT1 receptor is a single copy gene: characterization in a stable cell line

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.

Structural analysis and regulation of angiotensin II receptors

Angiotensin (Ang II) is an octapeptide hormone that plays a crucial role in the maintenance of electrolyte homeostasis and cardiovascular function. The hemodynamic and cardiovascular effects o f Ang II are mediated by high-affinity cell-surface receptors of the AT(1) pharmacologic class. The mammalian AT(1) receptor has recently been cloned and found to encode a 359-amino-acid protein of 41,000 molecular weight. The AT, receptor belongs to the guanine nucleotide regulatory-proteincoupled receptor family and is coupled to the phospholipase C signal transduction pathway as evidenced by intracellular calcium mobilization and inositol trisphosphate production upon receptor activation. Cloning of the AT(1) receptor has facilitated the study of structure-function correlates and molecular mechanisms of receptor regulation, and will lead to substantial progress in elucidating the mechanisms governing Ang II actions.

Immunological reactivity of angiotensin II receptor antagonists: possible implications for receptor binding sites

In the present study, we assessed the reactivity with seven anti-angiotensin II monoclonal antibodies of three nonpeptide and one peptide compounds described as selective antagonists of angiotensin II for AT1 (DuP 753, 2-n-butyl-4-chloro-5-(hydroxymethyl)-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl] methyl] imidazole; EXP 3174, 2-n-butyl-4-chloro-5-(carboxylic acid)-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl] methyl] imidazole) and AT2 receptor sites (CGP42112A, nicotinyl-Tyr-(N alpha-benzyloxycarbonyl-Arg)Lys-His-Pro-Ile-OH; PD123177, 1-[(4-amino-3-methylphenyl) methyl]-5-(diphenyl-acetyl)-4,5,6,7-tetrahydro-1H-imidazol[4,5-c] pyridine 6-carboxylic acid), respectively. These studies were undertaken because the reactivity of the monoclonal antibodies with peptide analogs of angiotensin II and the three-dimensional structure of an angiotensin II-immunoglobulin Fab fragment complex strongly suggested that the conformations identified by the monoclonal antibodies were relevant to those involved in receptor binding as defined by biophysical models supported by structure activity studies. Surprisingly although three of the compounds were described as competitive inhibitors of angiotensin II, binding of the various monoclonal antibodies to either ovalbumin-coupled angiotensin II adsorbed to plastic wells or 125I-labeled angiotensin II in liquid phase was unaffected by any of the nonpeptide antagonists and CGP42112A up to 10(-4) M concentration. The antagonists also failed to bind to rabbit polyclonal anti-angiotensin II antibodies. Direct binding experiments in which solid phase-immobilized angiotensin II and DuP 753 conjugates were incubated with anti-angiotensin II or anti-DuP 753 monoclonal antibodies, did not show any cross-reactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of polyclonal antibodies against angiotensin type 2 receptors

Murine neuroblastoma N1E-115 cells are a useful system in which to study neuronal angiotensin II (AngII) receptors. N1E-115 cells possess both type 1 (AT1) and type 2 (AT2) AngII receptor subtypes, as does mammalian brain. AT2 receptors in brain or N1E-115 cells can be solubilized in 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. In the present study, heparin-Sepharose chromatography was used to partially purify solubilized N1E-115 membranes to produce an enriched population of AT2 receptors. Subsequently, an eluted peak, containing the majority of AT2 binding activity, was used as an immunogen in the development of protein-directed polyclonal antibodies. The antibodies specifically detected immunoreactive proteins of approximately 110 and 66 kDa in both solubilized N1E-115 cells, as well as the original protein material that eluted from the heparin-Sepharose column, whereas no such immunoreactivity was detected in a kidney epithelial cell line that lacks any specific 125I-labeled AngII (125I-AngII) binding activity. Moreover, the antibodies immunoreacted with affinity-purified AT2 receptors. These antibodies were also able to immunoprecipitate AT2 receptors from solubilized N1E-115 cells, as revealed by the pharmacologic profile of 125I-AngII binding to the precipitated protein. Similarly, the antibodies were able to immunoprecipitate a 66-kDa protein that had been covalently crosslinked with 125I-AngII by use of the homobifunctional crosslinker dithiobis(succinimidyl propionate). Collectively, these results demonstrate the development of a specific AT2 receptor antibody that may be used to further characterize this receptor subtype at both the cellular and molecular levels.

Cellular expression of angiotensin type-1 receptor mRNA in the kidney

Angiotensin II has multiple renal effects that are important in the regulation of renal hemodynamics and electrolyte secretion, and binding sites for angiotensin II have been demonstrated in different cells of the kidney. In the present study the cellular localization of mRNA for the angiotensin type 1 (AT1) subtype of the angiotensin II receptor was studied in adult rat kidney using a cRNA probe and in situ hybridization. Strong labeling was demonstrated in tubule cells of the inner and outer stripe of the outer medulla. In emulsion-dipped sections, counter-stained with hematoxylin-eosin, labeling was identified in segment S3 of proximal tubules and in the thick ascending limb of loop of Henle (mTAL). The results suggest expression of AT1-receptor mRNA with a distinct compartmentalization within the nephron.