Showing papers on "Receptor published in 1977"
TL;DR: It is concluded that the opioid peptidergic system has agonists of different characteristics which interact with more than one type of receptor.
Abstract: Opioid peptides were assayed by inhibition of 3H-naloxone and 3H-leu-enkephalin binding in brain homogenates and by depression of contractions of the guinea pig ileum and mouse vas deferens. We conclude that the opioid peptidergic system has agonists of different characteristics which interact with more than one type of receptor.
2,443 citations
TL;DR: Experiments suggest that another important group of psychoactive drugs, the benzodiazepines, bind to specific receptors on the membranes of rat brain cells, and this suggests that there may be an unknown endogenous neurotransmitter which is the natural ligand for the Benzodiazepine receptor.
Abstract: HIGH affinity binding of tritium labelled morphine and morphine-like drugs to membranes in brain homogenates1–3 was a decisive advance in the characterisation of opiate receptors and the discovery of enkephalines and endorphines We report here experiments which suggest that another important group of psychoactive drugs, the benzodiazepines, bind to specific receptors on the membranes of rat brain cells This suggests that there may be an unknown endogenous neurotransmitter which is the natural ligand for the benzodiazepine receptor The binding sites are distributed unevenly through the brain, and displacement potencies of benzodiazepines correlate with pharmacological effects predictive of anxiolytic activity
1,399 citations
TL;DR: A division of adrenergic receptors into alpha and beta types could conceivably lead to the development of powerful agents even more selective for inhibition of renin release, control of blood pressure by a central site of action, reduction of fever, and possible other scientific or therapeutic applications.
796 citations
TL;DR: The relative quantity of these steroid receptors at the outer surfaces of cells from diverse tissues corresponds well with the capacity of a given cell to accumulate and retain oestrogen.
Abstract: OESTROGENS are more readily accumulated and retained in responsive cells than in cells that are not their targets1. Cytoplasmic macromolecules2 which specifically interact with oestradiol and other steroid hormones seem to mediate transfer of the agonist to the nuclear chromatin, where the complex is believed to promote expression of the phenotypic effects3–6. It is generally assumed that the hormone diffuses passively to “cytoplasmic” receptors which determine the cellular specificity of response7. But some experiments indicate that steroid hormones interact with components of biological membranes and may enter their respective target cells by a membrane-mediated process8–12 which is saturable and temperature-dependent13–17. We have investigated steroid-binding components associated with the plasma membranes of cells isolated from endometrium, liver and intestinal mucosa. Endometrial and liver cells show substantial binding to oestrogen immobilised by covalent linkage to an inert support, while intestinal cells have no such binding sites. The relative quantity of these steroid receptors at the outer surfaces of cells from diverse tissues corresponds well with the capacity of a given cell to accumulate and retain oestrogen.
692 citations
TL;DR: NGF can be shown to increase the survival, but not the division, of melanoma cells maintained in medium depleted of serum growth factors, similar to its effect on cultured sympathetic ganglion cells and on other cells derived from the neural crest.
Abstract: Purified mouse nerve growth factor (NGF)radiolabeled with 125I was tested for its ability to bind to a variety of different cultured cells NGF binds readily to human and hamster melanoma cells but does not bind to many other cell lines The three cell lines with the highest number of NGF receptors were derived from metastatic melanomas One of these lines, A875, was studied in detail and was shown to have approximately 7x10(5) NGF receptors per cell with an association constant of 10x10(9) liters/mole The use of these cells in competition binding assays permits the detection of 025 ng of NGF in various biologic fluids NGF can be shown to increase the survival, but not the division, of melanoma cells maintained in medium depleted of serum growth factors This effect of NGF as a specific "survival factor" appears analogous to its effect on cultured sympathetic ganglion cells and on other cells derived from the neural crest
615 citations
TL;DR: The distribution of opiate receptors, determined by the autoradiographic localization of stereospecific [3H]diprenorphine binding sites, was studied in the brain stem and associations of some receptors with small diameter axons, pupillary reflexes, hormonal control, and effects of opiates on neurotransmitter systems were discussed.
601 citations
TL;DR: It is demonstrated that thyroid hormones can regulate the number of cardiac beta-adrenergic receptors, and may be responsible, at least in part, for the enhanced catecholamine sensitivity of beta- adrenergic-coupled cardiac responses in the hyperthyroid state.
562 citations
Journal Article•
TL;DR: The data indicate that the cytotoxic lymphocyte in this system is Fc receptor positive, largely complement receptor negative, and may possess low density or low affinity receptors for SRBC.
Abstract: Using a series of techniques to identify and deplete various peripheral blood lymphocyte subpopulations, we studied the cytotoxic reactivity of normal individuals against the myeloid cell line K-562 in a 4-hr 51chromium-release assay. Depletion of lymphocytes bearing complement receptors had a variable, usually negligible effect on cytotoxicity. In contrast, depletion of lymphocytes bearing Fc receptors abrogated target cell lysis. Separation of lymphocytes with high-affinity binding of sheep red blood cells (SRBC) evidenced by rosette formation at 29 degrees C yielded a population of rosette-forming cells containing few cytotoxic cells, whereas separation of total E-RFC under optimal rosetting conditions produced a rosette fraction containing a major proportion of the effector cells. These data indicate that the cytotoxic lymphocyte in this system is Fc receptor positive, largely complement receptor negative, and may possess low density or low affinity receptors for SRBC.
460 citations
TL;DR: It is concluded that ACh receptors aggregate within the sarcolemma, spontaneously as well as in response to innervation, thereby contributing to the development of high receptor density in the subneural muscle membrane.
Abstract: 1. Theree-day-old cultures of myotomal muscle, obtained from embryos of Xenopus laevis, were stained with fluorescent conjugates of alpha-bungarotoxin and maintained in native toxin in order to ensure that ACh receptors subsequently inserted into the sarcolemma would not be stained. Neural tube cells were then added to the cultures. 2. When cultures were exmained 1-3 days later fluorescent stain was found to be associated with sites of nerve-muscle contact. In some cases the stain along the path of contact extended for greater distances than the patches of stain seen on non-contacted muscle cells. 3. The development of new areas of fluorescent stain at sites of nerve-muscle contact was confirmed by making successive observations on the same muscle cells over a period of a day. 4. Similar experiments on muscle cells not contacted by nerve revealed the formation of new receptor patches, usually in areas of cell growth. 5. The majority of fluorescent pathes on non-contacted muscle cells did not undergo changes in size or shape over the course of 1-2 days. However some examples of enlargement, shrinkage and disappearance were observed. 6. On the basis of these findings it is concluded that ACh receptors aggregate within the sarcolemma, spontaneously as well as in response to innervation. In the latter case extrajunctional receptors accumulate at the site of nerve contact thereby contributing to the development of high receptor density in the subneural muscle membrane. This process of receptors redistribution occurs in the absence of synaptic or contractile activity. 7. Possible mechanisms involved in the redistribution of ACh receptors are discussed in relation to those which appear to modulate ligand-induced changes in the distribution of lectin and immunoglobulin receptors.
452 citations
TL;DR: Preliminary clinical correlation of ER, PgR and response to endocrine therapy is encouraging, and it is found that the response rate is significntly higher if the tumor contains both ER and PgG than if the tumors contains ER alone.
Abstract: Regardless of the type of endocrine therapy employed objective tumor regression occurs in only 20-40% of breast cancer patients. With added combination chemotherapy an objective remission in 60% of patients may be achieved. Mammary glands contain specific receptors for hormones cytoplasmic proteins for steroids and cell surface receptors for polypeptides. Hormone-dependent tumors contain receptors but autonomous tumors often do not. The presence of estrogen receptor (ER) in a tumor does not guarantee that the tumor will behave in a hormone-dependent manner. The receptor sediments primarily at 8S in low salt sucrose gradients and at 4S in high salt sucrose gradients. ER values in primary tumors have ranged from 0 to 1000 fmol/mg of cytosol protein. ER values have been helpful in predicting results of endocrine therapy for matastatic breast cancer. When the ER value of the tumor is positive the response to endocrine therapy is 55-60%. Receptors for prolactin progestins and androgens have also been identified in breast tumors. Simultaneous analyses of these receptor proteins may be helpful in explaining the 45% with positive ER values who do not respond to hormone manipulation. In metastatic tumors when both progesterone receptor (PgR) and ER were present response to therapy was 81%. In some cases patients whose tumors have failed to regress after high doses of estrogens have responded to a combination of estrogen and progesterone. The synthetic progestin R5020 has been used to demonstrate PgR. Further studies of the biological responses of tumors not only to estrogens but also to glucocorticoids and progestins may permit a more precise description of the biochemical lesion in a tumor and the specific treatment to which it will respond.
401 citations
Journal Article•
TL;DR: In the presence of Triton X-100, GABA-receptor binding can be detected with considerable sensitivity using fresh or previously frozen tissue in the presenceof sodium, facilitating studies of GABA receptors in small tissue samples and increasing the sensitivity of radioreceptor assays for endogenous GABA.
Abstract: The effects of ions, detergents, and enzymes on γ-aminobutyric acid (GABA) binding to synaptic receptor sites in membranes of rat brain in the absence of sodium is contrasted with influences on sodium-dependent GABA binding. The anions thiocyanate, iodide, and nitrate increase the potency of the GABA antagonist bicuculline 10-fold in inhibiting sodium-independent GABA-receptor binding without affecting the potency of GABA agonists. Very low concentrations of the detergent Triton X-100 increase sodium-independent GABA-receptor binding up to 5-fold. In the presence of Triton X-100, GABA-receptor binding can be detected with considerable sensitivity using fresh or previously frozen tissue in the presence of sodium, facilitating studies of GABA receptors in small tissue samples and increasing the sensitivity of radioreceptor assays for endogenous GABA.
TL;DR: It is reported here that benzodiazepine receptors are also present in the human brain, that the cerebral and cerebellar cortical regions contain the highest densities of binding sites and that the receptors in human brain are very similar to those in rat brain.
Abstract: THE presence of brain-specific benzodiazepine receptors in membranes from rat brain is now established1–4. Highly significant correlations between the affinities of various benzodiazepines for the benzodiazepine receptor site in rat brain on the one hand and clinically predictive pharmacological activities in several species on the other, strongly suggest that the benzodiazepine receptor in vitro is related to a physiologically relevant receptor for benzodiazepines in vivo. We report here that benzodiazepine receptors are also present in the human brain, that the cerebral and cerebellar cortical regions contain the highest densities of binding sites and that the receptors in human brain are very similar to those in rat brain.
TL;DR: The action of these compounds as GABA agonists provides indirect evidence that GABA interacts with bicuculline-sensitive postsynaptic receptors in the cat spinal cord in a partially extended and almost planar conformation.
Abstract: COMPOUNDS which mimic the activity of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) on postsynaptic receptors are of particular pharmacological interest as possible therapeutic agents in human neurological disorders and as molecular probes with which to study different types of GABA receptors. The GABA molecule has considerable flexibility with free rotation around all three carbon–carbon bonds as indicated in Fig. 1. This conformational mobility is reduced in GABA analogues such as trans-4-aminocrotonic acid1 and muscimol2, which are potent GABA agonists at bicuculline-sensitive receptors on spinal neurones of the cat. The conformational mobility of such compounds can be reduced still further by incorporating the amino function in a ring structure. This has led to a new class of GABA agonist described here, based on l,2,3,6-tetrahydropyridine-4-carboxylic acid (isoguvacine) and the related bicyclic isoxazole 4,5,6,7-tetra-hydroisoxazolo[5,4-c]pyridin-3-ol (THIP) (Fig. 1). Isoguvacine represents a semi-rigid analogue of trans-4-aminocrotonic acid in a folded conformation. THIP, a folded analogue of muscimol, is even more rigid as the ‘masked’ carboxyl group (the 3-isoxazolo moiety) is fixed in the general plane of the molecule. The action of these compounds as GABA agonists provides indirect evidence that GABA interacts with bicuculline-sensitive postsynaptic receptors in the cat spinal cord in a partially extended and almost planar conformation.
TL;DR: The binding of formylNorleu-Leu-Phe to a site on rabbit neutrophils indicates that a natural bacterial product and synthetic formyl-peptides produce chemotaxis by the same receptor mechanism.
Journal Article•
TL;DR: The data indicate that effector cells in NK and ADCC are in overlapping, if not identical, subpopulations of Fc receptor-bearing lymphocytes of probable T cell lineage.
Abstract: Natural (or “spontaneous”) cytotoxicity against the K-562 myeloid cell line and antibody-dependent cellular cytotoxicity (ADCC) against sensitized Chang liver cells were monitored simultaneously in a 4 hr 51 Cr release assay, using the same preparations of normal human peripheral blood lymphocytes as effector cells. Both types of cytotoxic activity were expressed by lymphocytes bearing receptors for sheep erythrocytes and for the Fc portion of IgG. Up to 80% of the total natural killer (NK) cell and K cell (ADCC) activities were recovered in E-rosette pellets separated under optimal conditions. Since the ability to form rosettes with sheep erythrocytes is primarily a marker for human T cells, it seems likely that both NK and K cells are in the T cell lineage. Further, both NK and K cell cytolytic activities were severely depressed after brief exposure of lymphocyte suspensions or rosette pellets to ammonium chloride solutions. Both activities returned to normal values after 24-hr incubation at 24°C. Such sensitivity of human lymphocytes to ammonium chloride solutions may explain why other investigators have failed to observe NK or ADCC activity by E-RFC. When lymphocytes bearing Fc receptors were adsorbed onto plastic surfaces coated with a monolayer of immobilized antigen-antibody complexes made up of TNP and rabbit anti-TNP serum, both NK and ADCC activities were simultaneously depleted. Such depletion was completely blocked when Staphylococcal protein A, which binds selectively to the Fc portion of IgG, was incubated on the antigen-antibody monolayers before adding the lymphocytes. This confirmed that both NK and ADCC activities were mediated by effector lymphocytes bearing Fc receptors. When protein A at concentrations ranging from 0.01 to 100 µg/ml was added to the 51 Cr release assays, ADCC was significantly inhibited, presumably due to binding of protein A to available Fc sites of the sensitizing antibody. However, protein A had no effect on NK reactivity at any of the concentrations tested. When lymphocytes were treated for 30 min at 37°C with purified trypsin or α-chymotrypsin at concentrations from 0.01 to 10 mg/ml, NK activity was significantly inhibited whereas ADCC was unaffected. Other enzymes depressed (pronase, subtilisin) had no effect except at high concentrations (lipase), or stimulated (neuraminidase) both NK and K cell activity similarly, and therefore failed to distinguish between the effector cell types. Thus, our data indicate that effector cells in NK and ADCC are in overlapping, if not identical, subpopulations of Fc receptor-bearing lymphocytes of probable T cell lineage. The cytolytic mechanisms in NK and ADCC appear to be distinct, since we have been unable to find evidence for an “arming” antibody involved in this NK system.
TL;DR: It is indicated that long-term haloperidol treatment produces rather selective increases in dopamine/neuroleptic receptors, without much change in 4 other types of receptors.
TL;DR: Evidence is presented that three Escherichia coli phages use the major outer membrane proteins Ia, Ib, and II, respectively, as receptors, and that lipopolysaccharide may thus cause the specific localization of these proteins.
Abstract: Three Escherichia coli phages, TuIa, TuIb, and TuII, were isolated from local sewage. We present evidence that they use the major outer membrane proteins Ia, Ib, and II, respectively, as receptors. In all cases the proteins, under the experimental conditions used, required lipopolysaccharide to exhibit their receptor activity. For proteins Ia and II, an approximately two- to eightfold molar excess of lipopolysaccharide (based on one diglucosamine unit) was necessary to reach maximal receptor activity. Lipopolysaccharide did not appear to possess phage-binding sites. It seemed that the lipopolysaccharide requirement reflected a protein-lipopolysaccharide interaction in vivo, and lipopolysaccharide may thus cause the specific localization of these proteins. Inactivation of phage TuII by a protein II-lipopolysaccharide complex was reversible as long as the complex was in solution. Precipitation of the complex with Mg2+ led to irreversible phage inactivation with an inactivation constant (37 degrees C)K = 7 X 10-2 ml/min per microgram. With phages TuIa and TuIb and their respective protein-lipopolysaccharide complexes, only irreversible inactivation was found at 37 degrees C. The activity of the three proteins as phage receptors shows that part of them must be located at the cells surface. In addition, the association of proteins Ia and Ib with the murein layer of the cell envelope makes this pair trans-membrane proteins.
TL;DR: A general molecular mechanism for the process of capping, in which actin and myosin are directly involved, is proposed that membrane-associated actin is directly or indirectly bound to an integral protein or class of proteins, X, in the plasma membranes of eukaryotic cells.
Abstract: The mechanism of capping of cell surface receptors has been examined by a double fluorescence staining procedure that permitted simultaneous observations of the distribution of a surface-bound ligand together with intracellular actin or myosin. At an early stage in the capping of the T-25 antigen or the H2 histocompatibility antigens on mouse splenic T lymphocytes, or of concanavalin A receptors on HeLa cells, when the specific receptors in question were collected into patches that were distributed over the entire cell surface, the intracellular membrane-associated actin or myosin was also accumulated into patches that were located directly under the receptor patches. These and other results have led us to propose a general molecular mechanism for the process of capping, in which actin and myosin are directly involved. It is suggested that membrane-associated actin is directly or indirectly bound to an integral protein or class of proteins, X, in the plasma membranes of eukaryotic cells. When any receptor in the membrane is aggregated by an external multivalent ligand, the aggregate binds effectively to X, whereas unaggregated receptors do not bind to X. The receptor aggregates, linked to actin (and myosin) through X, are then actively collected into a cap by an analogue of the actin--myosin sliding filament mechanism of muscle contraction.
TL;DR: Concentration of antibodies to acetylcholine receptor in serum from patients with myasthenia gravis was measured using receptor from human muscle labeled with [ 125 I]α-bungarotoxin as antigen to suggest that it may be useful in diagnosis and monitoring immunosuppressive therapy.
TL;DR: It is reported here that propranolol a stereospecific affinity for the 5- HT receptor from rat brain which is similar in magnitude to the putative 5-HT receptor blocking drug methylsergide.
Abstract: ADVANCES in neurotransmitter receptor identification and quantification by biochemical techniques involving radiolabelled analogues of putative neurotransmitters have led to the characterisation of a number of receptor systems in mammalian brain tissue1; these include the catecholamines2,3, 5-HT4, glycine5 and GABA6 receptors. The development of these techniques has provided a means of screening chemical compounds for their effects on different receptor systems7. The central nervous system effects of (±)-propranolol (Inderal, ICI) in animals are well documented8,9. This drug has therapeutic benefit in man in anxiety10, and is also reported to have similar benefit in schizophrenia11,12, essential tremor13 and drug dependence14. The origin of these effects is not understood but theories about its mode of action include β-adrenergic blockade15, membrane stabilisation8 and a 5-HT receptor blocking action16,17. We report here that propranolol a stereospecific affinity for the 5-HT receptor from rat brain which is similar in magnitude to the putative 5-HT receptor blocking drug methylsergide.
TL;DR: Autoradiography indicates that the distribution of bound toxin reflects that of acetylcholine (ACh) receptors on these developing muscle cells, and most of the bungarotoxin binding could be inhibited by curare.
Abstract: 1. The distribution of α-bungarotoxin binding sites on embryonic and neonatal rat skeletal muscle fibres was determined by autoradiography. Most of the bungarotoxin binding could be inhibited by curare. This observation, together with the spatial distribution of toxin-binding sites, indicates that the distribution of bound toxin reflects that of acetylcholine (ACh) receptors on these developing muscle cells.
2. At 15 days of embryogenesis, muscle fibres showed an essentially uniform distribution of receptors. By 16 days, many fibres showed an accumulation of receptors in their mid-region. This accumulation was at the same location as histochemically demonstrated cholinesterase activity.
3. At 16 days ACh receptors were distributed over the entire length of the fibres, with a gradient of increasing density as the accumulation was appoached. The density of toxin binding sites in the accumulation was greater than the general level on 15 day cells, suggesting that the high junctional density does not develop solely by the loss of extrajunctional receptors.
4. The accumulations of ACh receptors became more pronounced and circumscribed with embryonic development, and after birth the extent of the localizations appeared to follow the size of the neuromuscular junction. The extrajunctional receptor density decreased with development, and by 1 week after birth was undetectable by the methods used.
5. The results suggest that the high junctional receptor density found on adult, innervated skeletal muscle fibres develops after the formation of the neuromuscular junction.
TL;DR: The occurrence of this ‘receptor mislocation mutation’ provides strong evidence for the role of the coated pit in the receptor-mediated uptake of lipoproteins and has implications for the structure and assembly of plasma membranes in mammalian cells.
Abstract: Low density lipoprotein is taken up by cultured human fibroblasts through an endocytic process that requires the binding of the lipoprotein to specific receptors located in coated pits on the cell surface. The coated pits are discrete segments of the plasms membrane that can undergo rapid invagination to form coated endocytic vesicles. In one form of the human genetic disorder familial hypercholesterolaemia, the responsible mutation produces altered lipoprotein receptors that lack the ability to become incorporated into coated pits. Instead, these mutant receptors are scattered at random over the entire plasma membrane. Becuase of their mislocation on the cell surface, the mutant lipoprotein receptors are unable to carry their bound lipoprotein into the cell. The occurrence of this 'receptor mislocation mutation' provides strong evidence for the role of the coated pit in the receptor-mediated uptake of lipoproteins. The data also have implications for the structure and assembly of plasma membranes in mammalian cells.
TL;DR: Findings may represent the converse of agonist-induced desensitization which is associated with decreases in beta-receptor number and provide a potential explanation for the clinically observed “propranolol withdrawal syndrome”.
TL;DR: Fluorescent concanavalin A (con A)-labelling showed that an electric field grossly redistributed con A receptors along the plasma membranes of living muscle cells within 4 h, which seemed to be electrophoretic in nature.
Abstract: Fluorescent concanavalin A (con A)-labelling showed that an electric field of 4 V cm-1 grossly redistributed con A receptors alone the plasma membranes of living muscle cells within 4 h. This field produced a voltage drop of 12 mV across these 30 micronm-wide cells. The movement of receptors was independent of cell metabolism and seemed to be electrophoretic in nature.
TL;DR: The results indicate that E3 acts as an estrogen antagonist when injected as a bolus because of the short nuclear retention time of RnE3 complexes, which suggests E3 is a potent estrogen without antagonistic properties.
Abstract: The relationship between nuclear retention or residency or receptor estrogen complexes and the agonistic and antagonistic properties of estriol was examined. Cytoplasmic estrogen receptor (Rc) and uterine weight were measured 24 and 48 h after treatment with estradiol (E2), estriol (E3), or or both hormones (E2 and E3). Levels of Rc were elevated in all groups at either time. Since levels of Rc were above control in each case, Rc does not appear to be the limiting factor in the antagonistic effect of estriol. Therefore, the effect of these steroids on translocation and retention of nuclear receptor estrogen complexes (RnE) was examined. Rats were injectd as above and RnE measured by 3[H] estradiol exchange 1, 3, and 6 h after injection. All treatments cause equal translocation of receptor of the nuclear compartment. However, by 6 h the quantity of Rn present in E2 treated animals was significantly above controls while that in E2 + E3 animals was intermediate. E3 alone failed to cause significant nuclear retention of Rn. These patterns of retention correlate with the weight and cytoplasmic receptor responses above and suggest that the short nuclear residency time of RnE3 complexes relates to the antagonism of E3. To test this, these estrogens were administered via paraffin pellets to maintain blood levels of each hormone. Levels of Rn were elevated 24 and 48 h after implant with no significant differences between treatment groups. Likewise, there were no differences in the growth response. Uterine weights were highly stimulated in all three cases (300% above control). These results indicate that E3 acts as an estrogen antagonist when injected as a bolus because of the short nuclear retention time of RnE3 complexes. However, when E3 is present continuously and RnE3 is elevated and maintained, E3 is a potent estrogen without antagonistic properties.
TL;DR: This work has measured the concentration of β-adrenergic receptors in crude membrane fractions of mononuclear cells from human subjects of various ages, and observed a significant decrease in receptor concentration in cells from older individuals.
Abstract: CONCENTRATIONS of certain hormone receptors are known to be reduced during ageing in several animal species1–4. Most relevant work, however, has been limited to intracellular hormone receptors such as those for steroids, and less is known about changes in cell surface receptors, including those for catecholamines. We have measured the concentration of β-adrenergic receptors in crude membrane fractions of mononuclear cells from human subjects of various ages. Receptor affinities for (—)3H-dihydroal-prenolol were esentially the same for all subjects. But a significant decrease in receptor concentration was observed in cells from older individuals.
TL;DR: The data suggest that the antibodies present in these three sera bind to different determinants on the insulin receptor, and these antibodies may be useful probes of receptor structure and function.
Abstract: Autoantibodies to the insulin receptor have been detected in the sera of several patients with the Type B syndrome of insulin resistance and acanthosis nigricans. In this study we have used three of these sera (B-1, B-2, and B-3) as probes of the insulin receptor in isolated rat adipocytes. Preincubation of adipocytes with each of the three sera resulted in an inhibition of subsequent [125I]insulin binding. 50% inhibition of binding occurred with serum dilutions of 1:5 to 1:7,500. As in our previous studies with other tissues, Scatchard analysis of the insulin-binding data was curvilinear consistent with negative cooperativity. Computer analysis suggested that in each case the inhibition of binding was due to a decrease in receptor affinity rather than a change in available receptor number.
In addition to the effects on insulin binding, adipocytes pretreated with antireceptor sera also showed alterations in biological responses. All three sera produced some stimulation of basal glucose oxidation. With serum B-3, maximal stimulation of glucose oxidation occurred at a serum concentration that inhibited binding by only 10-15%, whereas with serum B-2 the dilution curves for inhibition of binding and stimulation of glucose oxidation were superimposable. Serum B-1 behaved as a partial agonist; that is, it inhibited binding more effectively than it stimulated glucose oxidation. Cells pretreated with this serum in a concentration which inhibited binding by 80% also showed a five-fold shift to the right in the dose response of insulin-stimulated glucose oxidation, whereas spermine-stimulated glucose oxidation was unaffected. Serum B-2, which contained the highest titer of antireceptor antibodies, also stimulated 2-deoxy-glucose transport, as well as glucose incorporation into lipid and glycogen.
Both the ability of the serum to inhibit binding and stimulate glucose utilization were enriched in purified immunoglobulin fractions and retained in the F(ab′)2 fragment of the IgG. In addition, the bioactivity was blocked by antihuman IgG but not by anti-insulin antibodies. Enzymatic digestion of adipocytes with trypsin resulted in a complete loss of insulin-stimulated bioactivity of serum B-3, but had only minor effects on the glucose oxidation produced by serum B-1 or B-2.
These data suggest that the antibodies present in these three sera bind to different determinants on the insulin receptor. Thus, these antibodies may be useful probes of receptor structure and function.
TL;DR: Results suggest the involvement of a histaminic step in the action of NT, SP and MS, and suggest that steroid priming is required for TRF to exhibit PRL-releasing activity.
Abstract: Neurotensin (NT), substance P (SP) and morphine sulfate (MS) elevate plasma prolactin and growth hormone levels in both normal or estrogen-progesterone pretreated male rats. By contrast, steroid priming is required for TRF to exhibit PR.L-releasing activity. Naloxone, an opiate receptor blocker, reverses the stimulatory effect of MS only. Diphenhydramine, a histamine antagonist, inhibits the response to NT, SP and MS without affecting the response to TRF. These results suggest the involvement of a histaminic step in the action of NT, SP and MS. TRF, NT and SP do not appear to stimulate PRL and GH through activation of an opiate receptor. (Endocrinology 100: 751, 1977)
TL;DR: Mouse macrophages, activated in vivo or in vitro, were made to internalize sheep erythrocytes opsonized with IgG or IgM and complement, and experiments with cytochalasin B suggested that microfilaments were essential for the phagocytosis by Fc but much less important with the C3 receptor.
Abstract: Mouse macrophages, activated in vivo or in vitro, were made to internalize sheep erythrocytes opsonized with IgG or IgM and complement. Scanning electron microscopy and transmission electron microscopy were performed ac various times after the transfer of the cultures from conditions favoring attachment to conditions favoring internalization. The receptors for Fc and C3 were distributed randomly over the macrophage surface with the exception of the extreme periphery, were Fc receptors were more abundant. The E-IgG were ingested by means of thin membrane extensions rising from the macrophage surface and enclosing the opsonized particles tightly in a cup-like structure protruding from the macrophage surface. Only afterwards were the covered particles drawn into the cell body proper. The E-IgMC were seen to sink directly into the macrophage cytoplasm without apparent involvement of membrane extensions. Experiments with cytochalasin B suggested that microfilaments were essential for the phagocytosis by Fc but much less important with the C3 receptor.
Journal Article•
TL;DR: Results indicate that the specificity of inhibitory effects is related to receptor specificity, and dexamethasone is a potent inhibitor when cells are cloned in agarose, having a marked effect even at a concentration of 7 X 10(-9) M.
Abstract: Summary A human lymphoblastoid cell line (CEM), the growth of which is inhibited by glucocorticoids, is described. Although growth of the original uncloned cell line is only slightly retarded by dexamethasone, sensitive clones were isolated in which growth is completely blocked by 2 to 3 days of exposure to 10 -6 m dexamethasone. After 4 to 5 days, these cells become pyknotic and lyse. The inhibitory effect of dexamethasone first become apparent in suspension culture at a concentration of about 5 × 10 -8 m. Receptor analysis showed the presence of specific glucocorticoid receptors with an apparent dissociation constant for dexamethasone of about 1.3 × 10 -8 m both in the sensitive and in one resistant clone analyzed. Ability to displace dexamethasone from the receptor is correlated with the known glucocorticoid activity of all steroids tested, as is their ability to inhibit cloning of sensitive cells in agarose. These results indicate that the specificity of inhibitory effects is related to receptor specificity. Dexamethasone is a potent inhibitor when cells are cloned in agarose, having a marked effect even at a concentration of 7 × 10 -9 m. CEM cells thus provide human cell lines suitable for in vitro analysis of steroid effects on leukemic cells.