A kinetic comparative study on lymphocyte responses to superantigen and phytohemagglutinin: reciprocal presentation of superantigen on the surface of activated lymphocytes

The kinetics of thymidine incorporation into fractionated T lymphocytes responding to bacterial superantigens were compared to those of cells activated by phytohemagglutinin (PHA). Evident differences between the kinetics of cell proliferation induced by PHA-P and staphylococcal enterotoxin B (SEB) emerged after Day 4 of culture. PHA-P-induced proliferative responses of peripheral blood mononuclear cells (PBMCs) and fractionated cells were apparent on Day 4 because of the presence of accessory cells in the initial cell suspensions. This gradually diminished in correlation with the decline of accessory cells in the cultures. The SEB-induced cell growth (PBMCs and CD4+ cells), however, continued until Day 9 of the culture. This finding suggests the reciprocal usage of MHC class II molecules to present SEB by activated T lymphocytes for superantigen-induced T cell activation and suggests that superantigen-related immune activation may depend in part on the potential of activated T lymphocytes to mediate reciprocal cell-to-cell interactions in the presence of superantigens. The decline observed in the CD8+ cell response to SEB and toxic shock syndrome toxin-1 after Day 4 was revived by exogenous recombinant interleukin-2 (rIL-2) supplementation, suggesting that the consequent autocrine or paracrine secretion of IL-2 from the responding cells is essential for subsequent cell proliferation. SEB-induced cell proliferation was significantly suppressed by anti-CD11a (lymphocyte function-associated antigen-1; LFA-1, alpha-chain) monoclonal antibody, and the inhibitory effect was most obvious in 6-day cultured CD8+ lymphocytes. The results suggest that the lymphocyte response associated with the cell-to-cell copresentation of superantigens involves LFA-1 molecules as an accessory factor, particularly in CD8+ lymphocytes.

Immunohistochemical localization of metallothionein in the olfactory pathway of dogs

Dogs raised in the open air were used in this study. Metallothionein (MT) immunoreactivity was observed in the nucleus and/or cytoplasm of sustentacular cells of the olfactory epithelium in the nasal mucosa, whereas there was few MT-positive cells in the respiratory epithelium. MT immunoreactivity was also observed in astrocytes in all layers of the the olfactory bulb cortex; glial cells surrounding the glomeruli in the olfactory bulb showed prominent immunoreactivity for MT. Adult dogs exhibited stronger immunoreactivity for MT than young. Northern blot analysis demonstrated substantial levels of MT mRNA in the olfactory mucosa and olfactory bulb. Physiological roles of MT localized in the olfactory pathway of dogs were discussed.

The distribution of differentiated phenotypes of chondrocytes in osteoarthritic knee

Articular cartilage consists of chondrocytes and a cartilagenous matrix produced by these cells. The cartilaginous matrix is considered to undergo various changes in response to the surrounding environment. In this study, cartilaginous changes related to osteoarthritis of the knee were investigated. Histological changes were apparent in medical joint lesions, and changes typical of osteoarthritis, such as cell clustering and disruption of the matrix, were always observed. Degeneration was less severe in the lateral joint lesions. A biochemical analysis was undertaken and the molecular size of the proteoglycan produced in the matrix was measured by glycerol density gradient ultracentrifugation method, following pulse labeling with 35S-Sulfuric acid. The proteoglycan produced in the histologically altered regions tended to be of low molecular size. However, the size was still significantly larger than that of proteoglycans located in the nonarticular tissues such as synovia membrane, so the differentiated phenotype of chondrocytes persisted.

Role of platelet-activating factor and prostanoids in hemodynamic changes in rat experimental endotoxic shock

The present experiments were conducted to elucidate the role of platelet-activating factor (PAF) and cyclooxygenase products in the cardiovascular responses to endotoxin in anesthetized rats. Endotoxin (10 mg/kg, i.v.) induced hypotension that was accompanied by a decrease in cardiac output and an increase in calculated total peripheral resistance, suggesting that this hypotension mainly resulted from the reduced cardiac output. The endotoxin-induced decrease in cardiac output and hemoconcentration was significantly attenuated by TCV-309 (a PAF receptor antagonist), ibuprofen (a cyclooxygenase inhibitor) or S-1452 (a thromboxane A2/prostaglandin H2-receptor antagonist). During the 3-hr observation period following endotoxin administration, ibuprofen and S-1452 showed only early protection and TCV-309 showed late attenuation of the endotoxin-induced hypotension. Tachycardiac responses to endotoxin were only blocked by ibuprofen but not by TCV-309 or S-1452. These results suggest that both PAF and cyclooxygenase product(s), including thromboxane A2, mediate the decrease in cardiac output and hypotension in rat experimental endotoxic shock. Cyclooxygenase product(s) other than thromboxane A2 or prostaglandin endoperoxide may be involved in the endotoxin-induced increase in heart rate.

The role of physicochemical properties of biomaterials and bacterial cell adhesion in vitro

This study was undertaken to investigate the physicochemical aspects of the interaction between the surface of biomaterials and bacterial cell membranes in vitro, aimed at studying the mechanisms of bacterial adhesion to biomaterials. Correlations were made between the number of adherent bacterial cells (S. aureus) and each of the calculated components of surface free energy (i.e., dispersion, polarity and hydrogen bond) of biomaterials. The effect of antibodies to cell-adhesion molecules on bacterial adhesion was also studied using monoclonal antibodies to vitronectin receptor, fibronectin receptor and CD44. This study indicates the polarity component of surface free energy plays a dominant role in the process of bacterial adhesion at least in vitro. The number of cells adherent to materials decreased to 44-73% of the control value in the presence of antibodies tested, showing that cell adhesion molecules affect adherence to biomaterials. Moreover, the results suggested that bacterial adhesion was prevented by specific blockade of cell adhesion molecule receptors.

Evaluation of the subacute pulmonary and testicular inhalation toxicity of diborane in rats

This study aimed to clarify the subacute pulmonary and testicular inhalation toxicity of diborane (B2H6, CAS: 19287-45-7) in rats. Male Wistar rats were exposed for 8 weeks to 0.11 or 0.96 ppm of diborane for 6 hr/day, 5 days/week. The control group was exposed to filtered air. Bronchoalveolar lavage fluid (BALF), hematological, biochemical, and histopathological examinations were conducted. Sperm counts and spermatic morphological changes were examined in epididymides, and histopathological examination was carries out in testes. BALF examinations revealed that the percentage of neutrophils increased in a dose-dependent manner and that of macrophages decreased in rats exposed to 0.96 ppm. Quantities of total and individual phospholipids in BALF increased in rats exposed to 0.96 ppm. The proportion of phosphatidylglycerol plus sphingomyelin decreased, and phosphatidylethanolamine and phosphatidylinositol increased in rats exposed to 0.96 ppm. LDH increased in rats exposed to 0.96 ppm, and ALP showed a dose-dependent increase. In serum, alpha 1-antitrypsin and superoxide dismutase activities increased in rats exposed to 0.11 or 0.96 ppm. These changes showed dose-dependent effects on the lung in rats exposed to diborane, possibly indicating that the hyperenergia of type II cells with proliferation and/or hypertrophy without histopathological changes occurred even in rats exposed to 0.11 ppm. Testicular examinations revealed no particular findings. The TLV-TWA of diborane (0.1 ppm) seems to be high and possibly unsafe, considering that the no-observed-effect level over 8 weeks for rat lung was under 0.11 ppm.

[A clinical evaluation of fluconazole in deep seated fungal infections associated with hematological disorders]

The effectiveness of fluconazole on deep seated fungal infections associated with hematological disorders was evaluated in a multicenter clinical study. The underlying diseases included acute myeloblastic leukemia, acute lymphocytic leukemia, malignant lymphoma, adult T cell leukemia, multiple myeloma and others. Fluconazole (FLCZ) was administrated 100-400 mg/day intravenously or orally to 79 patients with systemic fungal infections complicated with hematological disorders and it was possible to evaluate clinical efficacies in 60 patients. 27 patients were diagnosed as having determinate systemic fungal infections and 33 patients suspected fungal infections. The clinical efficacies were 81.5% (22/27) in patients with diagnosed fungal infections and 57.6% (19/33) in patients with suspected fungal infections. The overall clinical efficacy was 68.3% (41/60). No side effects such as gastrointestinal symptoms, vascular pain and renal dysfunction were observed in this study. As for abnormal laboratory test, transient increases in GOT, GPT, Al-P, LDH, serum Na, Cl and decrease in serum K were observed in 9 patients (11.4%). These results indicated that FLCZ has a high therapeutic efficacy on deep seated fungal infections in patients with hematological disorders.

Production of chronic compression of the cauda equina in rats for use in studies of lumbar spinal canal stenosis

STUDY DESIGN

The pathophysiology of lumbar spinal canal stenosis was analyzed with a new model in rats.

OBJECTIVES

To produce chronic compression of the cauda equina in rats for analysis of the pathophysiology of lumbar spinal canal stenosis.

SUMMARY OF BACKGROUND DATA

Models of compression to date have involved acute or subacute compression. A model of chronic compression has not been available.

METHODS

A stainless steel wire fastened around the spine at L5 in 3-week-old rats, with a plate inserted against the ventral aspect of the vertebra to protect it from the wire. as the rats grew, the wire cut into the spinal canal. One year after the operation, canal stenosis was present without paralysis of the back limbs.

RESULTS

Stenosis seen in sagittal sections, as a percentage of the original width, was 51.6 +/- 6.2% (mean +/- standard deviation). In histologic analysis of the region near the wire, findings included axonal degeneration, demyelination, vacuolar degeneration of the nerve fibers, and narrowing the intradural blood vessels with a decrease in their number. Cephalad and caudad to the wire, congested intradural blood vessels, degenerative foci near these congested vessels, fibrosis around these foci, congested epidural vessels, and fibrosis around these vessels were observed. During electrophysiologic analysis (six rats with stenosis), the conduction velocity of the cauda equina was found to be delayed.

CONCLUSIONS

The histologic and electrophysiologic findings in this animal model were similar to findings in human subjects, so rats prepared in this way should be useful for study of chronic compression of the cauda equina.

A rare case of sarcoidosis with rheumatoid arthritis

Sarcoidosis shows many of the clinical and immunological abnormalities and is a multi-organ granulomatous disease of unknown cause which has histological features of non-caseous epithelioid granuloma formation. Sarcoidosis is rarely coexisted rheumatoid arthritis. Although such arthropathy if occur is thought to manifest rheumatoid changes, the current presence of sarcoidosis and rheumatoid arthropathy has been reported by very few histological studies. We experienced a case of combination of sarcoidosis and rheumatoid arthritis both of which were histologically confirmed. This patient initially developed small papules on the face and was diagnosed as having sarcoidosis after one year. Later, she showed symptoms and signs of polyarthritis and was confirmed to have sarcoidosis and rheumatoid arthritis in combination by histological analysis. We present this case with some reference to literatures.

Clinical effect of etidronate disodium (EHDP) on heterotopic ossification following total hip arthroplasty

We investigated the status of the development of heterotopic ossification and compared the frequency of heterotopic ossification in the EHDP group with that in the untreated (control) group to evaluate the efficacy and safety of EHDP. Seventy-seven patients who had undergone total hip arthroplasty or femoral head prosthesis for the treatment of osteoarthritis and femoral neck fracture were enrolled in the study. Heterotopic ossification surrounding the hip joint was evaluated according to the roentgenographic classification. In the control group, heterotopic ossification was found in 10 patients (20%) during the period, while in the EHDP group, it was found in one patient (3.7%) during the treatment period after the operation. Gastrointestinal disorder, in one case only was a side effect observed during EHDP treatment. It was revealed that EHDP inhibits heterotopic ossification following total hip replacement in patients with osteoarthritis.

Correction of dorsi-flexed intercalated segment instability after restoration of scaphoid height in a cadaver model of scaphoid non-union

Models of scaphoid non-union with static dorsi-flexed intercalated segment instability were produced in five frozen arms from cadavers or subjects following accidents by repetitive mechanical loading of the wrist joints longitudinally after a bone defect has been made at the mid-portion of the scaphoid. We designed four models of reduction: anatomical reduction; reduction with a shortened scaphoid; anatomical reduction but with the radio-lunate ligament sectioned, and a shortened scaphoid with the radio-lunate ligament sectioned. Results suggested that anatomical reduction with rigid fixation with a Herbert screw was most effective for correction of malalignment with DISI. Preservation of the radio-lunate ligament during the palmar approach to the scaphoid seemed to be important to prevent ligamentous carpal instability.

Parallel induction of cecropin and lysozyme in larvae of the silkworm, Bombyx mori

Lysozyme activity in the hemolymph of Bombyx mori increased in parallel with cecropin activity after injection of the larvae with soluble peptidoglycan or UV-killed bacteria. The lysozyme and cecropin A genes were expressed in parallel in the fat body after injection of peptidoglycan as detected by northern blot hybridization. The elicitor specificity for lysozyme induction was identical to that for cecropin, suggesting a common mechanism for recognition of bacteria and following signal transduction introducing to the simultaneous synthesis of cecropin and lysozyme. Bacterial cells killed by UV-irradiation were also effective as elicitor when added to the fat body culture, suggesting that phagocytosis of bacteria by hemocytes may not be an essential process for the induction of antibacterial protein synthesis in the silkworm.

Role of porins in the antibiotic susceptibility of Pseudomonas aeruginosa: construction of mutants with deletions in the multiple porin genes

We inserted deletions in the chromosomal genes of Pseudomonas aeruginosa coded for the outer membrane porins, proteins C, D2, or E1, and all possible combinations of these proteins by the gene replacement technique and selecting for imipenem-resistance. Determination of the minimum inhibitory concentrations of beta-lactams, fluoroquinolones, chloramphenicol and gentamicin in these mutants revealed that most mutants showed equal susceptibility to the porin-sufficient strain. The only exception was that imipenem and meropenem showed increased minimum inhibitory concentrations in all of the mutants lacking protein D2. These results firmly established that the P. aeruginosa porins identified so far form the pores do not accommodate the passage of most antipseudomonal antibiotics, with the exception of carbapenems.

Augmented lung adenocarcinoma cytotoxicity by the combination of a genetically modified anti-Lewis Y antibody and antibodies to complement regulatory proteins

Complement-dependent cytotoxicity (CDC) mediated by a chimeric anti-Lewis Y monoclonal antibody (cH18A; human IgG1) was investigated in this study. Human lung adenocarcinoma cell lines (PC7, PC9, and PC14) were used as the target cells. PC7 and PC9 cells, expressed Lewis Y antigen and were lysed by cH18A as effectively as by the parent mouse anti-Lewis Y antibodies (mH18A) in a concentration-dependent manner. PC14 cells did not express Lewis Y antigen and were not lysed by either cH18A or mH18A. cH18A mediated CDC activity against PC7 and PC9 cells was enhanced by the combined use of monoclonal antibodies directed against CD46(MCP), CD55(DAF), and CD59. These molecules are complement-regulatory proteins which protect host cells from CDC. PC7 and PC9 cells, showed high levels of surface expression of these proteins, PC7 cells were more susceptible to cH18A-mediated CDC than PC9 cells. Use of multiple blocking antibodies to the complement-regulatory proteins produced more enhancement of cH18A-mediated CDC than a single antibody. Moreover, expression of CD55 and CD59 by PC7 and PC9 cells was decreased after treatment with PI-PLC, resulting in increased susceptibility to cH18A-mediated CDC. Although the reason is unknown, PC7 cells became more susceptible to CDC than PC9 cells after PI-PLC treatment even in the absence of cH18A. These data suggest that chimeric monoclonal antibodies can be used to induce CDC against lung adenocarcinoma, and that such CDC is potentiated by a variety of antibodies blocking compliment-regulatory proteins on the tumour cell surface.

Radiological evaluation of disease progression in rheumatoid arthritis

X-ray photographs of the wrist joints in 210 cases of Rheumatoid Arthritis (RA), who visited an outpatient clinic for RA in Orthopedic Department of the Osaka City Medical School were investigated using Carpo-Metacarpal Ratio (CMR) and Shinomiya's criteria, more detailed classification system based on the staging criteria of Steinbrocker. Radiological staging of the wrist joints revealed a correlation with the duration of RA and was considered to be a useful parameter in disease assessment. Radiological alterations in the wrist joints were progressive, but with great individual differences.

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.

Serum concentrations of granulocyte colony-stimulating factor (G-CSF) determined by a highly-sensitive chemiluminescent immunoassay during the clinical course of subacute thyroiditis

Granulocyte colony-stimulating factor (G-CSF) concentrations in serum were determined for the first time by a newly developed and highly sensitive chemiluminescent immunoassay (the limitation of detection, 0.5 pg/ml) in ten patients with subacute thyroiditis, during treatment with glucocorticoid or indomethacin. Before therapy, circulating neurophil counts significantly increased to 5.15 +/- 2.07 x 10(3)/microliters compared with the convalescent phase (2.94 +/- 1.07 x 10(3)/microliters), and the data were correlated with individual serum G-CSF levels (r = 0.854, P < 0.01). Serum concentrations of interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were less than the detectable threshold of ELISA. During two weeks of glucocorticoid therapy, although the circulating neutrophil counts increased from 5.15 +/- 2.46 x 10(3)/microliters to 7.73 +/- 1.64 x 10(3)/microliters (P < 0.01), serum G-CSF levels were depressed from 25.1 +/- 15.3 pg/ml to 13.8 +/- 13.9 pg/ml (P < 0.01). These data indicate that G-CSF is one of the mediators of the increase of neutrophils in subacute thyroiditis, while it does not contribute to steroid-induced neutrophilia.

Disulfide bridges in extracellular domains of angiotensin II receptor type IA

Angiotensin II receptor type IA (AT1A) has a cysteine (Cys) residue in each of four extracellular domains, and these Cys residues are believed to form two disulfide bridges. However, the question as to which pairs of Cys residues form disulfide bridges have not been experimentally determined. We constructed four mutants of rat AT1A, in which extracellular Cys residues were individually replaced by glycine (mutant C-1, C-2, C-3 and C-4). Further, we constructed two double mutants, in which two extracellular Cys residues were simultaneously substituted for by glycine. The binding affinity for angiotensin II in a double mutant C-1 + 4 (Cys18,274Gly) was similar to that in individually substituted mutants (C-1, C-2, C-3 and C-4) whereas the ligand binding of a double mutant C-2 + 4 (Cys101,274Gly) was completely abolished. The bindings of the non-peptide AT1A antagonist [125I]EXP-985 to mutants C-1, C-4 and C-1 + 4 were only slightly reduced whereas in mutant C-2, C-3 and C-2 + 4 the specific binding for [125I]EXP-985 was completely abolished. These results suggest that disulfide bridges in AT1A are formed between Cys18 and Cys274, and between Cys101 and Cys180, and the latter disulfide bond is essential for the binding of the non-peptidic antagonists [125I]EXP-985 or losartan.

Oxidative DNA damage induced by silica in vivo

Occupational exposure to silica has often been associated with the development of pulmonary fibrosis and, occasionally, lung cancer. Their development may be mediated by oxidant-induced cellular injury. The short- and long-term effects of a single intratracheal instillation of silica in rats (10 mg/200 microliters/saline per rat) was assessed by measuring 8-hydroxy-2'-deoxyguanosine (oh8dG) levels in lung tissue and peripheral blood leukocytes. Cell differentials, reduced glutathione (GSH), and superoxide dismutase (SOD), lipid peroxide, and total phospholipids in peripheral blood and/or bronchoalveolar lavage fluid (BALF) were also measured. The pulmonary oh8dG levels increased approximately 2.24- 2.86-fold from 1 to 5 days after exposure to silica. It was still elevated 1 and 4 weeks after installation, but the difference was no longer statistically significant. The oh8dG levels in peripheral blood leukocytes were never significantly different, but they were generally higher than in the controls. The low SOD levels in the BALF of exposed rats in the early stage and the higher GSH levels in the late stage may represent protective reactions against the generation of oxygen species. A significant increase in oh8dG levels in lung tissue suggested the possible carcinogenicity of silica.

Tissue- and development-specific expression of goat insulin-like growth factor-I (IGF-I) mRNAs

We cloned four kinds of goat insulin-like growth factor-I (IGF-I) cDNAs. Each of them encodes the same mature IGF-I and different signal peptides. In this study, we analyzed expression of the four kinds of mRNAs in tissues in various developmental stages by a reverse transcriptase-polymerase chain reaction assay. The results suggest that their expression may be controlled by different promoters, the activities of which are tissue- and development-specific.

Cloning, expression and regulation of angiotensin II receptors

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.

Dynamic aspects in the expression of the goat insulin-like growth factor-I (IGF-I) gene: diversity in transcription and post-transcription

Goat IGF-I (gIGF-I) cDNA was cloned using the reverse transcriptase-polymerase chain reaction (RT-PCR). The cDNA, which was homologous to rat class 1 IGF-I cDNA, was 969 bp long. From the open reading frame found in it, we predicted a 154 amino acid protein consisting of a 49 amino acid signal peptide, a 70 amino acid mature IGF-I peptide, and a 35 amino acid E domain (the COOH-terminal peptide). From the gIGF-I gene, we isolated and sequenced some segments containing four exons that encompassed the entire gIGF-I cDNA sequence. Goat liver RNA was analyzed by RT-PCR, and the nucleotides of the RT-PCR products were sequenced and checked with the nucleotide sequences of the segments from the gIGF-I gene. The gene had three leader exons (1W, 1, and 2, from upstream to downstream) and was transcribed into three kinds of mRNAs (classes 1W, 1, and 2). Another RNA species was detected by RT-PCR analysis of exon 1W. We sequenced it and found that in this transcript, the 3'-portion of exon 1 was inserted between exons 1W and 3, resulting in class 1W-1 del. mRNA. That is to say, the gIGF-I gene had three leader exons and four kinds of mature mRNA.

Role of carboxyl tail of the rat angiotensin II type 1A receptor in agonist-induced internalization of the receptor

Binding of angiotensin II (Ang II) to its receptor type 1A (AT1A) is known to trigger its internalization. We studied the role of cytosolic segments of AT1A in the internalization, and obtained results indicating a functional role of the cytosolic carboxyl terminal tail of AT1A in the internalization. Deletion of 50 amino acids from the carboxyl terminus abolished the receptor internalization. Deletion mutants lacking 13 and 32 amino acid residues in the carboxyl terminal cytosolic region were internalized to the same extent as wild type AT1A; however, internalization of a mutant lacking the last 42 residues was partially suppressed. Thus, residues 310 through 327 were shown to be essential for the internalization. We propose that a short domain in the cytoplasmic tail (residues 310 to 327) may play a dominant role in the agonist-induced receptor internalization of AT1A. Our results also suggest that the molecular determinants of the AT1A receptor involved in receptor internalization are distinct from those participating in the desensitization process.