Showing papers on "Receptor published in 1975"

Complement and immunoglobulins stimulate superoxide production by human leukocytes independently of phagocytosis.

Abstract: Human peripheral blood polymorphonuclear leukocytes, when exposed to appropriate stimuli, generate significant amounts of superoxide anion (O-.2), a highly reactive molecule which is possibly involved in bacterial killing. Since the subcellular localization and mechanism of activation of O-.2 generating systems are unknown, we have investigated superoxide dismutase-inhibitable cytochrome c reduction (attributable to O-.2) by, and lysosomal enzyme release from, normal polymorphonuclear leukocytes and cells rendered incapable of ingesting particles by treatment with cytochalasin B. Neither phagocytosis nor lysosomal degranulation were prerequisites for enhanced O-.2 generation. Cytochalasin B-treated cells exposed to (a) serum-treated zymosan, a C3b receptor stimulus; (b) heat aggregated human IgG, an Fc receptor stimulus; and (c) the complement component, C5a, generated enhanced amounts of O-.2 in a time and concentration-dependent fashion. These cells also responded by releasing lysosomal enzymes, but there was no correlation between the ability of any immune reactant to provoke enzyme release and its ability to stimulate O-.2 generation. The three stimuli also enhanced O-.2 generation by normal (untreated) polymorphonuclear leukocytes, but only serum-treated zymosan and aggregated IgG were capable of provoking lysosomal enzyme release from normal cells. Untreated zymosan and native IgG neither stimulated O-.2 production nor provoked lysomal enzyme release. Since enhanced O-.2 production was stimulated by immune reactants in the absence of phagocytosis, the O-.2 generating system is very likely associated with the external plasma membrane of the polymorphonuclear leukocyte. Leukocyte membrane receptors for complement and immunoglobulins may therefore not only serve in particle recognition but also may initiate biochemical events which accompany phagocytosis and killing.

Studies on the mechanism of phagocytosis. I. Requirements for circumferential attachment of particle-bound ligands to specific receptors on the macrophage plasma membrane.

Abstract: These experiments were designed to evaluate the role of macrophage plasma membrane receptors for the third component of complement (C) and for the Fc portion of IgG in the ingestion phase of phagocytosis. Sheep erythrocyte (E) were coated with anti-E IgG [E(IgG)]; these E(IgG) were then attached to cultivated monolayers of mouse peritoneal macrophages under conditions which reversibly inhibit ingestion of E(IgG). The E(IgG)-macrophage complexes were further incubated under similar conditions with an antimacrophage IgG fraction which blocks Fc receptor-mediated ingestion but has no effect upon ingestion mediated by other phagocytic receptors. When these cultures were subsequently incubated under conditions optimal for particle ingestion, phagocytosis of the IgG-coated erythrocytes did not occur; the erythrocytes remained bound to the Fc receptors of the macrophage plasma membrane. To determine whether ligands must cover the entire surface of an attached particle to permit ingestion of that particle, C-coated E [E(IgM)C] were bound to the C receptors of thioglycollate-induced (activated) macrophages at 4 degrees C. E(IgM)C-macrophage complexes were then trypsinized at 4 degrees C, a procedure which resulted in cleavage of erythrocyte-bound C3b molecules to a form of C3 not recognized by the macrophage receptors for C3b. Under the conditions used, trypsin did not affect the attachment of E(IgM)C to the macrophage surface or the macrophage receptors for C3b. When these trypsin treated E(IgM)C-macrophage complexes were incubated at 37 degrees C, the bound E(IgM)C were not ingested; the erythrocytes remained attached to the macrophage plasma membrane via the macrophage's C receptors. These results indicate that attachment of a particle to specific receptors on the macrophage plasma membrane is not sufficient to trigger ingestion of that particle. Rather, ingestion requires the sequential, circumferential interaction of particle-bound ligands with specific plasma membrane receptors not involved in the initial attachment process.

Predicting response to endocrine therapy in human breast cancer: a hypothesis.

Abstract: We hypothesize that the presence of progesterone receptors in human breast tumors may be a sensitive marker for predicting response to endocrine therapy. Progesterone receptors were found in 56 percent of tumors with estrogen receptors, but were absent in tumors without estrogen receptors. Preliminary clinical correlations show that only those breast tumors with progesterone receptors regressed after endocrine therapy.

Studies of the macrophage complement receptor. Alteration of receptor function upon macrophage activation.

Abstract: We have examined the roles of Fc receptors and complement receptors in mediating the interaction of sensitized sheep erythrocytes (E) with activated and with nonactivated mouse peritoneal macrophages. Both activated and nonactivated macrophages ingest IgG-coated erythrocytes [E(IgG)]; activated cells intest 1.5-2 times as man E(IgG) as do nonactivated macrophages. Thus, there is a quantitative difference in Fc receptor-mediated ingestion between activated and nonactivated macrophages. There is, however, a qualitative difference in function of complement receptors of activated and nonactivated macrophages. Nonactivated macrophages avidly bind complement-coated E [E(IgM)Ia1, but do not ingest them to a significant degree. Activated macrophages, on the other hand, bind and ingest E(IgM)C. The possibility of Fc receptor participation in mediating ingestion of E(IgM)C by activated macrophages was eliminated by blocking Fc receptors with an antimacrophage IgG fraction. Activated macrophages treated with antimacrophage IgG did not ingest E(igG) but did ingest both E(IgM)C AND E(IgM)C. Nonactivated macrophages treated with antimacrophage IgG did not interact at all with E(IgG). These cells bound, but did not ingest, E(IgM)C and E(IgM)C. Complement receptor-mediated ingestion is a marker for macrophage activation and may be physiologically important in the elimination of complement-coated particles.

Morphine receptors as regulators of adenylate cyclase activity

Abstract: Morphine inhibits adenylate cyclase (EC 4.6.1.1) activity of neuroblastoma times glioma hybrid cells. The inhibition is stereospecific and is reversed by the antagonist, naloxone. The relative affinities of narcotics for the opiate receptor agree well with their effectiveness as inhibitors of adenylate cyclase. Morphine-sensitive and -insensitive cell lines were found, and the degree of sensitivity was shown to be dependent upon the abundance of narcotic receptors. Thus, morphine receptors are functionally coupled to adenylate cyclase. A molecular mechanism for narcotic addiction and tolerance is proposed.

Human epidermal growth factor: isolation and chemical and biological properties

Abstract: A polypeptide hormone has been isolated from human urine, human epidermal growth factor. It was assayed by its ability to compete with 125I-labeled mouse-derived epidermal growth factor in binding to human foreskin fibroblasts. The biological effects of the human polypeptide are similar to those previously described for the mouse hormone. These include the stimulation of the growth in vitro of human foreskin fibroblasts and corneal epithelial cells in organ culture, and the in vivo induction of precocious eyelid opening in the newborn mouse. The amino acid compositions of the two polypeptides differ, although certain similarities are present. The estimated molecular weight of the human polypeptide, 5300-5500, is slightly lower than that of the mouse hormone. Both polypeptides apparently compete for the same site on the cell membrane; and antibodies to the mouse polypeptide crossreact to some extent with the human hormone.

Adrenergic and cholinergic receptors in the human prostate, prostatic capsule and bladder neck.

Abstract: The adrenergic and cholinergic receptors of the human prostatic capsule, prostatic "adenoma", and bladder neck, were investigated by the in-vitro isometric technique. The prostatic capsule was found to be very rich in both alpha-adrenergic receptors and cholinergic receptors. The prostatic adenoma was moderately rich in alpha-adrenergic receptors, but cholinergic receptors were absent. Beta-adrenergic receptors were absent in the prostatic adenoma, and there was an equivocal response in less than half the specimens of the prostatic capsule. An attempt was made to distinguish between the trigonal component at the posterior bladder neck, and the true bladder neck muscle both posteriorly and antero-laterally. The results indicat that the "posterior bladder neck" seen at operation is predominantly trigonal muscle, and is poor in cholinergic receptors. The adrenergic response is variable in the true bladder neck muscle, but is present and strong in the trigonal muscle. This response is characteristically gradual in its development. In view of the findings in this investigation, it is suggested that certain instances of acute retention of urine in prostatic patients are due to over-stimulation of the alpha-adrenergic receptors, particularly those in the prostatic capsule. Similarly, the accepted clinical contraindication to the use of cholinergic drugs for retention in the prostatic patient is supported by the distribution of the cholinergic receptors in the tissues examined.

Antibodies that impair insulin receptor binding in an unusual diabetic syndrome with severe insulin resistance

Abstract: Six patients with a unique form of diabetes associated with extreme insulin resistance have markedly reduced insulin binding to specific receptors on their circulating monocytes. When normal insulin receptors were exposed to serum or immunoglobulin fractions from three of these patients in vitro the specific binding defect was reproduced.

Catecholamine-induced subsensitivity of adenylate cyclase associated with loss of beta-adrenergic receptor binding sites

Abstract: Injection of frogs with beta-adrenergic catecholamines for 1-24 hr produces marked subsensitivity of the erythrocyte membrane adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1.] to in vitro stimulation by isoproterenol. The subsensitization is specific for catecholamine stimulation, since basal and fluoride-stimulated enzyme activity are unaffected. Maximum isoproterenol-stimulated adenylate cyclase activity declines by 75% in the isoproterenol-treated animals (P less than 0.001). The concentration of isoproterenol causing one-half maximal activation of adenylate cyclase, however, is unaltered. (-)[3H]Alprenolol, a potent competitive beta-adrenergic antagonist, was used to study directly the beta-adrenergic receptor binding sites in the erythrocyte membranes from control and subsensitized animals. A highly significant (P less than 0.005) 60% fall in the number of the beta-adrenergic receptor binding sites ("specific"(-)[3H]alprenolol binding sites) in the treated animals was found. The binding affinity of the sites was not markedly altered. These data suggest that beta-adrenergic catecholamines are able to regulate catecholamine sensitivity of tissues in vivo, by regulating the properties of the beta-adrenergic receptor binding sites.

Acetylcholine receptor turnover in membranes of developing muscle fibers.

Abstract: [125I mono-iodo-alpha-bungarotoxin is used as a specific marker in a description of acetylcholine receptor metabolism. It is concluded that acetylcholine receptors in the surface membranes of chick and rat myotubes developing in cell cultures have a half-life of 22-24 h. Alpha-bungarotoxin (bound to a receptor which is removed from the membrane) is degraded to monoiodotyrosine which appears in the medium. Several observations are consistent with a model in which receptors or alpha-bungarotoxin-receptor complexes are internalized and then degraded: (a) the rate of appearance of iodotyrosine does not reach its maximal rate until 90 min after alpha-bungarotoxin is bound to the surface receptors; (b) 2,4-dinitrophenol, reduced temperature, and cell disruption all inhibit the degradation process. The degradation of surface receptors is not coupled to the process by which receptors are incorporated into the membrane. Evidence suggest that receptors are incorporated into the surface membrane from a presynthesized set of receptors containing about 10% as many alpha-bungarotoxin binding sites as does the surface. Additionally, a third set of acetylcholine receptors is described containing about 30% as amny binding sites as does the surface. These "hidden" recptors are not precursors yet are not readily accessible for binding of extracellular alpha-bungarotoxin. These findings are discussed in relation to both plasma membrane biosynthesis and control of chemosensitivity in developing and denervated skeletal muscle.

Steroid hormone receptors

Abstract: Publisher Summary This chapter discusses different aspects of steroid hormone receptors. Steroid hormones show different kinds of activities when examined at the physiological level. Differences may be also classified in terms of gross biological responses. Studies of the development of male secondary sex organs and hypothalamus in mammals, and of the oviduct in avians and batracians suggest that hormones such as estradiol or testosterone can promote the formation of morphologically and functionally stabilized new type of cells, enough to justify thinking in terms of differentiation processes. There are intracellular specific protein receptors for binding steroid hormones, all properties of which are compatible with the assumption that they are receptors. It is found that when estradiol, estrone, and estriol are compared, the rate of dissociation of uterine receptor steroid complexes is similar for the three steroids, but the rate of association is slower for the two lower affinity ones than for estradiol. The kinetic parameters of the binding reaction of the uterine receptor-estradiol are also studied.

Estrogen-Induced Uterine Responses and Growth: Relationship to Receptor Estrogen Binding by Uterine Nuclei11

Abstract: The relationship between estrogen receptor (R) binding by uterine nuclei and uterotrophic responses was examined. Immature rats received a single injection of estradiol (E2) or estriol (E3) and the following parameters were measured: accumulation and retention of the estrogen receptor by the nucleus of uterine cells; incorporation of 14C-glucose into CO2, lipid, protein and RNA; RNA polymerase activity; water imbibition and increased dry weight. E2 and E3 were of equal potency with regard to the rapid accumulation of R by the nucleus but differed with respect to long term retention of R. The concentrations of nuclear RE2 and RE3 complexes were equivalent between 1 and 3 hr after estrogen injection; however, by 6 hr RE2 remained significantly elevated while RE3 levels had fallen to control values. E2 and E3 were also of equal potency with respect to the stimulation of enhanced glucose utilization, water imbibition, the incorporation of 14C-glucose into lipid, protein and RNA 3 hours following an injection ...

Search for an Endogenous Ligand for the Opiate Receptor

Abstract: It was investigated whether there is an endogenous factor in the brain which binds to the opiate receptor in neural tissue. Extracts from rat brain were processed in different ways; fractions were assayed for ability to inhibit the receptor binding of dihydromorphine. There was no evidence for high-molecular weight substances or lipid soluble substances with such ability. On the other hand, processing of an acid water extract of brain except the cerebellum (which was negative) yielded an active fraction with receptor blocking activity. This fraction was heat stable, polyionic and had an apparent molecular weight of 1000-1 200 dalton. These and other characteristics indicate that it might well be a peptide. The factor inhibited binding to the opiate receptor in synaptic plasma membranes of rat brain and to the receptor of the guinea-pig ileum although it was less effective on the latter, particularly after long-term incubation. The interaction between the factor and dihydromorphine was reversible and apparently competitive.

In vitro models in the study of structure-activity relationships of narcotic analgesics.

Abstract: Evidence has been adduced for the view that the morphiness receptor or receptors in the myenteric plexus of guinea pig ileum are very similar to the brain receptors that mediate the analgesic action of the narcotic alagesics. Such an in vitro model is very suitable for the study of structure-activity relationships because the angonist and antagonist activities of compounds can readily be assessed. One example is the investigation of the effects of changes at the N atom. Another point of interest is the role of substitutions at the C14 atom in morphine and morphinans. Such alterations in structure may have a profound effect on the relative agonist and antagonist activities and may convert a drug with dual agonist and antagonist actions into an antagonist devoid of agonist action.

Binding of monomeric immunoglobulins to fc receptors of mouse macrophages.

Abstract: The binding properties of surface receptors of immunoglobulins on mouse macrophages were studied with mouse myeloma proteins and normal peritoneal macrophages, thioglycollate-stimulated macrophages, and a macrophage cell line, P388D1. Primary cultures of mouse embryo fibroblasts served as controls. IgG2a proteins were bound strongly;IgG2b was bound weakly (one-twentieth as well as IgG2a);IgM, IgA, and IgG1 were not bound significantly. The number of binding sites per cell for IgG2a was 4 X 10(5) for thioglycollate-stimulated cells and 1 X 10(5) for normal and P388D1 cells. Binding was exothermal: with decreasing temperature the equilibrium (association) constants increased and dissociation rate constants decreased (at 37degreesC the respective values were 2 X 10(7) M-1 and 0.26 min-1, the latter value corresponds to a half time for dissociation of 2.6 min). From the rapidity of association and dissociation, it appears that the surface of the macrophage is in a dynamic equilibrium with IgG2a molecules in the cell's immediate microenvironment. The receptors for IgG2a are clearly specific for determinants in the immunoglobulin constant domain: two IgG2a proteins with greatly different isoelectric points (determined by isoelectric focusing) were bound with the same affinity to the same receptors; moreover, the Fc fragment was bound and Fab fragments were not. The Fc receptors for IgG2a proteins were readily eliminated by exposing macrophages briefly to trypsin. The receptors were regenerated during subsequent cultivation in serum-free medium; regeneration was inhibited totally by cycloheximide and partially by actinomycin D.

Thyrotropin-releasing hormone regulates the number of its own receptors in the GH3 strain of pituitary cells in culture

Abstract: Thyrotropin-releasing hormone (TRH), a hypothalamic tripeptide, binds rapidly and reversibly to specific membrane receptors on GH3 cells, a clonal strain of rat pituitary cells grown in culture. GH3 cells were incubated for 1-72 hr with unlabeled TRH, washed, and then incubated for 1 hr with [3H]TRH. Under these conditions 80% of any bound, unlabeled TRH exchanges with [3H]TRH in the medium, and the amount of radioactivity bound to the cells gives a measure of the number of TRH receptors. In GH3 cells, the number of available TRH receptors decreased from 92% of control after 1 hr to 35% after 48 or 72 hr of incubation with unlabeled TRH. Binding of [3H]TRH to both intact control and TRH-treated cells was half-maximal at 8 nM [3H]TRH, but the maximum amount of [3H]TRH bound was decreased by 75% in cells previously incubated for 48 hr with unlabeled TRH. Equilibrium binding studies were performed using membrane fractions prepared from control cells and cells previously exposed to TRH for various periods. The dissociation constant of the TRH-receptor complex was the same in all cases, but the maximum amount of TRH bound decreased progressively in membrane fractions from cells incubated with TRH for 1-51 hr. TRH receptors were not found in cytoplasmic fractions of control or TRH-treated cells. The loss of TRH receptors was reversible within 4 days. In the continued presence of the tripeptide the number of receptors remained low for 12 days. After incubation for 2 days with different concentrations of TRH, the number of receptors was decreased to 33% of control at 100-300 nM TRH, and half of this decrease occurred at about 1 nM TRH; half-maximal biological responses occur at 2 nM TRH. The biologically active Ntau-methylhistidyl derivative of TRH also effected a loss of receptors, while three inactive analogs of TRH did not cause reductions in the number of TRH receptors. In cultures incubated for 40 hr with cycloheximide, protein synthesis was inhibited by 85%, but the number of TRH receptors was 76% of control suggesting that the receptor has a long half-life. When GH3 cells were incubated with cycloheximide plus TRH, the number of TRH receptors decreased by only 23% as compared to a decrease of 73% in cells incubated with TRH alone, suggesting that receptor loss is partially dependent on active protein synthesis. We conclude that in GH3 cells TRH regulates the number of its own receptors.

Insulin Receptor Deficiency in Genetic and Acquired Obesity

Abstract: We have previously shown that in the insulin-resistant obese hyperglycemic mouse (ob/ob) there is a deficiency in the number of insulin receptor sites on hepatocytes, adipocytes, and thymic lymphocytes. We now find that concentration of insulin receptors on liver plasma membranes is decreased in the db/db mouse, another form of inherited obesity, and in normal mice that became obese after treatment with gold thioglucose, while thin mice, heterozygous for the ob mutation (ob/+), have normal insulin binding. With acute and chronic food restriction of the ob/ob and gold thioglucose obese mice, there is reduction in hyperinsulinemia and an associated increase in the insulin receptor concentration toward normal. In contrast, when fasting ob/ob mice were given exogenous insulin to maintain the hyperinsulinemia, insulin receptors failed to increase. Thus, in all cases, there was a consistent relationship between the degree of hyperinsulinemia and of insulin receptor loss. These findings suggest that decreased insulin binding is a characteristic feature of the insulin resistance of obesity, and that sustained hyperinsulinemia is a major factor in the control of the concentration of insulin receptors on target cells.

Prolactin receptors in rat liver: possible induction by prolactin.

Abstract: A prolactin receptor, present in adult female rat liver, can be induced in males by estrogen. Hypophysectomy diminished receptor levels in the female and rendered males unresponsive to estrogen. A renal pituitary implant blunted the decrease in hypophysectomized females and induced the receptor in hyophysectomized males. The increased receptor level in hypophysectomized males with a renal pituitary implant was preceded by a sustained elevation of circulating prolactin. Our observations suggest that prolactin induces its own receptor.

Rapid changes in rat pineal beta-adrenergic receptor: alterations in l-(3H)alprenolol binding and adenylate cyclase.

Abstract: The properties of the beta-adrenergic receptor which regulates adenylate cyclase [ATP pyrophosphate-lyase (cyclizing)8 EC 4.6.1.1] in the pineal gland are similar to the properties of the sites which specifically bind l-[3H]alprenolol, a potent beta-adrenergic antagonist. Stimulation of the beta-adrenergic receptor results in a 30-fold increase in the activity of N-acetyltransferase (= arylamine acetyltransferase; acetyl CoA:arylamine N-acetyltransferase, EC 2.3.1.5), an enzyme involved in the synthesis of thepineal hormone melatonin. In the normal diurnal light-dark cycle there is greater physiological stimulation of the beta-adrenergic receptor in the pineal during the night than during the day. Pineals from rats kept in constant light for 24 hr possess more hormone-sensitive adenylate cyclase and specifically bind more l-[3H]alprenolol than do pineals from rats kept in the dark overnight. When rats, exposed to light for 24 hr, are treated with the beat-adrenergic agonist isoproterenol, there is a rapid loss of both hormone-sensitive adenylate cyclase activity and specific l-[3H]alprenolol binding sites. There is no change in the affinity of adenylate cyclase for isoproterenol or for its substrate, ATP. Similarly, although there are fewer binding sites, there is no change in the affinity of the remaining sites for either agonist or antagonist. Inhibition of protein synthesis with cycloheximide does not affect the loss of either adenylate cyclase activity or specific binding sites. The data suggest that stimulation of the beta-adrenergic receptor causes a rapid decrease in the number of available receptors and in hormone-sensitive adenylate cyclase activity; conversely, lack of stimulation causes an increase in these parameters. It is suggested that these changes contribute to the phenomena of super- and subsensitivity in the pineal gland by regulating the capacity of the pineal to synthesize cyclic AMP in response to beta-adrenergic stimulation.

Chemical differentiation of histamine H1- and H2-receptor agonists.

Abstract: Histamine exists predominantly as the NT-H tautomer of the monocation (IIa) at a physiological pH of 7.4 and structure-activity studies indicate that this tautomer is likely to be the pharmacologically active species for both H1 and H2 receptors. Effective H2-receptor agonists appear to require a prototropic tautomeric system whereas H1-receptor agonists do not need to be tautomeric. This identifies a chemical difference in the receptor requirements which provides the basis for obtaining selective histamine H1-receptor agonists. Thus 2-(2-aminoethyl)thiazole and 2-(2-aminoethyl)pyridine are nontautomeric and are highly selective agonists for histamine H1 receptors (H1:H2 ca. 90:1 and 30:1, respectively). In conjunction with the selective H2-receptor agonist, 4-methylhistamine, they are of great value for studying the pharmacology of histamine receptors.

Defect in insulin binding to receptors in obese man. Amelioration with calorie restriction.

Abstract: With insulin at 0.1 ng/ml, the binding of (125I)insulin in vitro to circulating lymphocytes from 11 obese patients was less than that observed with cells from 10 thin volunteers. Furthermore, with obese cells, unlabeled insulin was less effective in competing with labeled hormone for binding, both at low and high concentrations of unlabeled insulin. These differences were not accounted for by the high concentrations of insulin in the circulation of the obese patients at the time fthe blood was drawn, or by differences in degradation of hormone, or in the characteristics of the cell population. The decrease in binding appears to be due to a lowering of the receptor concentration, but some loss of affinity has not been excluded. Institution of a calorie restricted diet (nine patients) which ameliorated the hyperinsulinemia, produced an improvement in hormone binding. Since the insulin receptors of lymphocytes in metabolic disorders seem to reflect the state of insulin receptors or target cells such as liver and fat, the lymphocytes or other leukocytes appear to be ideal for studies of impaired cell responsiveness to hormones in man.

Differential effects of protein-modifying reagents on receptor binding of opiate agonists and antagonists.

Abstract: Opiate receptor binding is enhanced by prior incubation, which removes an endogenous inhibitor of receptor binding. Protein-modifying reagents which affect sulfhydryl groups differentially influence the binding of agonists and antagonists to the opiate receptor. These reagents, including iodoacetamide, N-ethylmaleimide, mercuriacetate, mersalyl acid, p-aminophenylmercuric acetate, and p-chloromercuribenzoate, strongly inhibit [3H]dihydromorphine binding at concentrations which do not affect [3H]naloxone binding. Prior treatment with opiates protects the receptor binding from reagents. The reagents decrease the apparent number of dihydromorphine binding sites without altering their affinity, and also increase the sensitivity of agonist binding to the inhibitory effects of sodium.

Direct identification and characterisation of beta-adrenergic receptors in rat brain.

Abstract: MODULATION of cellular function by the autonomic nervous system is accomplished, at least in part, by the stimulation of β-adrenergic receptors by catecholamines at neuroeffector junctions1. Activation of these receptors results in stimulation of adenylate cyclase with increased intracellular levels of cyclic AMP. The β-adrenergic receptors of a variety of non-neural tissues have been characterised indirectly by measurement of altered adenylate cyclase activity or of intracellular cyclic AMP in response to β-adrenergic agonists and antagonists. Direct characterisation of the β-adrenergic receptors in avian2,3 and amphibian4 erythrocytes and in canine heart5 has been accomplished by binding assays using radioactive β-adrenergic antagonists.

Characterization of the macrophage receptro for complement and demonstration of its functional independence from the receptor for the Fc portion of immunoglobulin G.

Abstract: The complement receptor of the macrophage membrane recognizes particle-bound C3b but does not recognize particle-bound C3d. C3-b-coated sheep erythrocytes were bound to macrophages via their C3b receptors, and the preparations were then incubated with either latex particles or opsonized pneumococci (test particles). Macrophages ingested the test particles, but erythrocytes were not ingested; they remained bound to C3b receptors of the macrophage plasma membrane. Thus, a signal initiating ingestion via one type of receptor is not transmitted to all receptors which have the potential to mediate phagocytosis.