Showing papers on "Receptor published in 1972"

Differentiation of the transmembrane Na and Ca channels in mammalian cardiac fibres by the use of specific inhibitors

Abstract: According to earlier studies on mammalian papillary muscles, verapamil and compound D 600 (a methoxy-derivative of verapamil) can abolish the Ca dependent contractile responses completely whilst the Na dependent action potentials persist. In an attempt to clarify the mechanism of action separate measurements of the transmembrane Na and Ca currents have been performed on ventricular trabeculae of cats using a special voltage clamp technique. The following results were obtained: As a functional significance of this dual membrane transport system it is possible to change the contractile force by inotropic substances which act on the Ca conductivity without a corresponding influence on excitation.

Culture of Enzymatically Dispersed Anterior Pituitary Cells: Functional Validation of a Method

Abstract: A method for preparing short—term enzymatically dispersed pituitary cell cultures is described. It has been used to assay hypothalamic releasing factors. The cells secrete TSH or LH and FSH in amounts directly related to the dose of TRF or LRF respectively. The minimal active doses of synthetic TRF and either synthetic or highly purified ovine LRF is ca. 10-10M. Apparent affinity constants for TRF or LRF receptors are ca. 10-9M. Enhanced secretion rates of TSH or LH of 8– to 20–fold in response to maximal levels of TRF or LRF are routinely observed. The sensitivity of the cultured cells to TRF and LRF is maintained for more than 2 weeks in culture although the magnitude of the secretory response and the intracellular hormone content declines with time in culture. Chronic administration of TRF or LRF depletes the intracellular hormone levels while simultaneously increasing the total TSH or LH content in the culture (tissue and fluid). As has been observed with other in vitro systems, high medium potassium,...

The Use of Dopamine β-Hydroxylase as a Marker for the Central Noradrenergic Nervous System in Rat Brain

Abstract: Improvements in the method for localization of dopamine-β-hydroxylase by immunofluorescence allow the observation of noradrenergic-cell bodies, non-terminal fibers, and axon terminals in the rat brain. The distribution of the hydroxylase correlated well with the results obtained by localization of norepinephrine. Dopamine-β-hydroxylase was not observed in dopaminergic neurons or terminals, indicating that these cells do not have the capacity to synthesize norepinephrine. The use of the hydroxylase as a marker, however, has made it possible to visualize noradrenergic nerve terminals on small arteries in the brain parenchyma that have not been described by catecholamine-fluorescence histochemistry. The source of the terminals on small arteries appears to be central noradrenergic neurons rather than the peripheral sympathetic nervous system. Dopamine-β-hydroxylase generally was not observed in the large arteries of the brain parenchyma. These observations suggest that cerebral microcirculation is regulated by central noradrenergic neurons.

Three acetylcholine receptors in Aplysia neurones

Abstract: 1. In the pleural ganglion of Aplysia californica, groups of cells were identified that respond differently to an iontophoretic injection of ACh. The anterior neurones are excited by ACh, whereas the medial cells are inhibited. The inhibitory response is biphasic, consisting of a short-latency, rapid component and a longer-latency, slow component. Homologous responses (e.p.s.p.s in the anterior cells and a two-component inhibitory response in the medial cells) are evoked in these same cell groups by stimulation of an identifiable presynaptic neurone. 2. The e.p.s.p. and the corresponding ACh potential are completely eliminated by hexamethonium which has no effect on either of the inhibitory potentials. Both the e.p.s.p. and the rapid i.p.s.p. (and the corresponding ACh potentials) are blocked by tubocurarine, dihydro-β-erythroidine, strychnine and brucine. These drugs have no effect on the slow inhibitory potential, whether elicited synaptically or by ACh injection. The slow response can be selectively blocked by methylxylocholine, tetraethylammonium (TEA), and phenyltrimethylammonium (PTMA). Since the three types of potentials were found to be differentially affected by ACh antagonists, it was concluded that the various responses are due to activation of three different ACh receptors. 3. Of the cholinomimetics tested, only carbamylcholine imitates all three actions of ACh. Nicotinic agents, which were shown to activate the two curare-sensitive receptors, have no stimulating effect on the curare-insensitive receptor. This latter receptor can be selectively stimulated by arecoline. The cholinomimetics were shown to have a secondary blocking effect on the receptor(s) they stimulate. 4. Muscarine, even at high doses, is ineffective as either a stimulating or a blocking agent on any of the three receptor types. The muscarinelike drugs oxotremorine, methacholine, and pilocarpine have only weak and non-specific cholinomimetic action on these receptors. Their blocking effects are likewise negligible. 5. The two curare-sensitive receptors, which are presumably the same as those described by Tauc & Gerschenfeld (1962), respond like vertebrate nicotinic receptors to both cholinomimetics and cholinolytics. The third receptor type, on the other hand, has a unique pharmacological profile. It is unaffected by both nicotine and muscarine, and is blocked neither by curare nor by atropine. Knowing that it can be stimulated by arecoline and blocked by methylxylocholine, TEA and PTMA does not facilitate its incorporation into the classical scheme of cholinergic receptors.

Evidence for a receptor recognizing antigen complexed immunoglobulin on the surface of activated mouse thymus lymphocytes.

Abstract: The distribution in the mouse of lymphoid cells carrying receptors for IgG or IgG-Ag was investigated. B lymphocytes were found to have receptors reacting with both IgG and IgG-Ag. Resting T lymphocytes did not react with IgG-Ag. T lymphocytes activated by passage through irradiated, allogeneic mice had a receptor reacting with IgG-Ag, but not with IgG.

Adaptation in Skate Photoreceptors

Abstract: Receptor potentials were recorded extracellularly from the all-rod retina of the skate after the application of sodium aspartate. This agent suppresses the responses of proximal elements, but leaves relatively unaffected the electrical activity of the photoreceptors (a-wave) and pigment epithelium (c-wave). Since the latter develops too slowly to interfere with the receptor response, it was possible to isolate receptor potentials and to compare their behavior in light and dark adaptation with earlier observations on the S-potential, b-wave, and ganglion cell discharge. The results show that the photoreceptors display the full complement of adaptational changes exhibited by cells proximal to the receptors. Thus, it appears that visual adaptation in the skate is governed primarily by the photoreceptors themselves. Of particular interest was the recovery of sensitivity in the presence of background fields that initially saturate the receptor potential. Analysis of this recovery phase indicates that a gain-control mechanism operates within the receptors, at a distal stage of the visual process.

Acetylcholine receptors. Distribution and extrajunctional density in rat diaphragm after denervation correlated with acetylcholine sensitivity

Abstract: Using 125iodine-labeled α-bungarotoxin (α-BGT-125I) and quantitative radioautography, we have studied the time-course of the change in acetylcholine (ACh) receptor distribution and density occurring in rat diaphragm after denervation. In innervated fibers, ACh receptors are localized at the neuromuscular junction and the extrajunctional receptor density is less than five receptors per square micrometer. The extrajunctional receptor density begins to increase between 2 and 3 days after denervation and increases approximately linearly to 1695 receptors/µm2 at 14 days, subsequently decreasing to 529 receptors/µm2 at 45 days. We have isolated plasma membranes from rat leg muscles at various times after denervation and find that the change in concentration of ACh receptors in the membranes measured by α-BGT-125I binding and scintillation counting follows a time-course similar to the change in ACh receptor density measured radioautographically. Furthermore, we have correlated extrajunctional ACh receptor density measured by radioautography with extrajunctional ACh sensitivity measured by iontophoretic application of ACh and intracellular recording and find that the log of ACh receptor density is related to 0.53 times the log of ACh sensitivity. These results are discussed in terms of the electrophysiological experiments on the ACh receptor and the recent, more biochemical approaches to the study of ACh receptor control and function.

The structure of erythrocyte membranes studied by freeze-etching. II. Localization of receptors for phytohemagglutinin and influenza virus to the intramembranous particles.

Abstract: The distribution of specific glycoprotein receptors on the external surfaces of red cells was mapped, by the freeze-etching technique, to determine if the receptors coincided with the underlying 75-A intramembranous particles. Phytohemagglutinin, ferritin-conjugated phytohemagglutinin, and influenza virus were used as labeling agents since they can be seen by freeze-etching techniques and each reacts with a different site on the same glycoprotein molecule. The distribution of these labels was studied on intact human red cells, isolated ghost membranes, and trypsin-treated ghost membranes. The results show that the receptors for these labels are distributed uniformly over the surfaces of normal red cell membranes in the same apparent distribution as that of the 75-A particles within the membrane. The association between the external receptors and the underlying particles is especially evident when trypsin-treated ghost membranes are labeled: the labeled receptor sites and the intramembranous particles both form sharply defined, reticulated networks, which overlap. These results provide further support for the idea that membrane-bound glycoproteins are oriented so that their carbohydrate-rich segments, which bear the antigenic sites and receptors, are exposed to the external medium, while hydrophobic segments of the same molecules interact with lipids, and possibly other proteins, to form the intramembranous particles.

Effects of chemicals on receptors and horizontal cells in the retina

Abstract: 1. By applying atomized chemical solutions on to gecko and carp retinae, neuropharmacological reactions of the photoreceptors and horizontal cells were observed. 2. Sodium L-glutamate and L-aspartate, glycine, ACh and GABA, had no appreciable effect on the photoreceptor activity. 3. Carp horizontal cells were depolarized by both L-glutamate and L-aspartate. When maximally depolarized, the action of the endogenous transmitter from the receptor terminals was completely masked, resulting in abolition of the S-potentials. 4. Responses to red light in both L- and C-type horizontal cells were more strongly affected by aspartate than responses to blue light. 5. Glycine and GABA hyperpolarized the horizontal cells, and the S-potentials were diminished. 6. ACh had no effect on the activity of the horizontal cells.

Restriction of the Mobility of Lymphocyte Immunoglobulin Receptors by Concanavalin A

Abstract: The induction by anti-immunoglobulin of patch and cap formation on mouse lymphocytes was inhibited by the addition of concanavalin A. This effect was reversed by α-methyl-D-mannoside, a competitive inhibitor of the binding of concanavalin A. Concanavalin A prevented both patch and cap formation, in contrast to the metabolic inhibitor NaN3, which prevented only cap formation. This suggests that binding of concanavalin A induces changes on or in the lymphocyte membrane that inhibit free diffusion of immunoglobulin receptors.

The mechanism of antigenic stimulation of primary and secondary clonal precursor cells

Abstract: Cell transfers to carrier-immunized irradiated mice have permitted an analysis of the in vitro stimulation of clonal precursors of anti-2,4-dinitrophenyl (DNP) antibody-producing cells derived from both immune and nonimmune mice. The results indicate that: (a) carrier-specific enhancement is obligatory for stimulation of primary precursor cells and increases both the size and number of detectable foci derived from secondary precursors. (b) This carrier-specific enhancement is most apparent in the stimulation of precursors of high-affinity antibody producer cells. (c) The antibody produced by primary foci, like that of secondary foci, appears homogeneous. (d) The frequency of clonal precursors in normal spleens is 38% that in spleens from mice 4-8 months after immunization, and the number of such precursors in normal spleens can be reduced fivefold by specific suppression of donor mice with soluble antigen. (e) The average of association constants of primary monofocal antibodies, like that of primary serum antibody produced in carrier-primed mice, is less than 10-fold lower than that of secondary clonal or serum antibody. (f) The affinity of primary monofocal antibodies shows a slight dependence on stimulating antigen concentration; however, a minimum threshold affinity consonant with stimulation is apparent. (g) Free hapten inhibits antigenic stimulation of primary precursor cells at a much lower concentration than is required for the inhibition of secondary precursors. These results are interpreted as indicating that (a) primary stimulation, like secondary stimulation, results from the selective stimulation by antigen of a population of cells differing from one another in their potential antibody product but each having only a single such product; (b) the antigen receptors of primary cells interact with antigen as if they are monovalent while receptors of secondary cells evidence multivalence; (c) antigenic stimulation appears to require both a relatively high affinity of receptors for bound antigen and an interlinking of receptors through such antigen; stimulation is thus seen as resulting from a stabilization of receptors within antigen-receptor aggregates to the cell surface; (d) T-cells appear to serve both in cross-linking antigens and in amplifying the size of stimulated clones.

Inhibitory and excitatory effects of dopamine on Aplysia neurones

Abstract: 1. Electrophoretic application of dopamine (DA) on Aplysia neurones elicits both excitatory and inhibitory effects, which in many cases are observed in the same neurone, and often result in a biphasic response. 2. The DA receptors are localized predominantly on the axons. Desensitization, which occurs after repeated injections or with bath application of DA, is more marked for excitatory responses. 3. Tubocurarine and strychnine block the DA excitatory responses without affecting the inhibitory ones, which can be selectively blocked by ergot derivatives. It is concluded that the excitatory and inhibitory effects are mediated by two distinct receptors. 4. The two DA receptors can be pharmacologically separated from the three ACh receptors described in the same nervous system. 5. In some neurones the dopamine inhibitory responses can be inverted by artificial hyperpolarization of the membrane at the potassium equilibrium potential, EK, indicating that dopamine causes a selective increase in potassium permeability. 6. In other neurones the reversal potential of dopamine inhibitory responses is at a more depolarized level than EK, but can be brought to EK by pharmacological agents known to block the receptors mediating the excitatory effects of DA. 7. In still other neurones, the hyperpolarization induced by DA cannot be inverted in normal conditions, but a reversal can be induced by ouabain or by the substitution of external sodium by lithium. These results are discussed in terms of an hypothesis in which dopamine increases the potassium permeability of a limited region of the axonal membrane. 8. It is concluded that a selective increase in potassium permeability probably accounts for all dopamine inhibitory effects in the neurones studied.

Role of DNA and Specific Cytoplasmic Receptors in Glucocorticoid Action

Abstract: Glucocorticoids induce tyrosine aminotransferase (EC 2.6.1.5) synthesis in cultured rat hepatoma cells. These steroids penetrate the cell membrane and bind to specific cytoplasmic receptor proteins. The resulting complex binds to the nucleus. This nuclear binding has now been studied in a cell-free preparation. The reaction appears to require a temperature-dependent modification of the steroid-receptor complex. There is a fixed number of nuclear sites that are half saturated at a complex concentration of 6 to 24 x 10(-11) M. Treatment with deoxyribonuclease destroys nuclear-binding capacity. The complex also binds to purified HTC cell DNA with characteristics similar to the binding to isolated nuclei, and, as in intact cells, receptors complexed with an anti-inducer steroid bind very poorly to DNA. These data suggest that the nuclear sites for binding steroid-receptor complexes are on the DNA. Since the extent of complex binding to purified DNA exceeds that observed with isolated nuclei, chromosomal proteins may act to restrict binding to certain regions of the DNA. These studies suggest that steroid hormones stimulate the synthesis of specific proteins by affecting the transcription of structural or regulatory genes.

Angiotensin II Vascular Receptors: Their Avidity in Relationship to Sodium Balance, the Autonomic Nervous System, and Hypertension

Abstract: During intravenous administration of varying doses of angiotensin II antibody to anesthetized rats, apparently specific vascular receptors were characterized. These receptors compete with administered antibody to bind circulating angiotensin. This competitive phenomenon was used to evaluate the affinity of these receptors for angiotensin. Apparent vascular receptor affinity was defined by the amount of antibody required to block the blood pressure response to exogenous angiotensin. It was found that this receptor affinity varies directly with sodium intake so that the amount of antibody required to block was eightfold greater in normal animals on a high sodium intake, as compared with those on a low sodium intake. Sodium dependence of receptors was also demonstrated in nephrectomized animals, in desoxycorticosterone (DOC)-treated rats, and in chronic renal hypertension. Thus the observed changes in receptor affinity were usually inversely related to measured endogenous angiotensin II levels. Ganglionic blockade increased antibody requirement eightfold. All of these changes were consistent, with no overlap observed in response of individual animals from different groups. These results may explain the variation in pressor activity of angiotensin associated with changes in salt balance and ganglionic blockade. In general, when sufficient antibody was injected to block the effect of exogenous angiotensin a blood pressure lowering effect was also observed. Two exceptions were the nephrectomized and the one-kidney renal hypertensive animals, in both of which antibody administration had no effect on blood pressure. Additional results suggest that changes in receptor affinity are involved in the pathogenesis of various types of experimental hypertensions because the amount of antibody required to block angiotensin was enhanced in renal (twofold), DOC (fourfold), and genetic (fourfold) hypertension. Accordingly, changes in the affinity of these receptors could be critically involved in normal blood pressure control and in various forms of experimental and clinical hypertension, even when circulating angiotensin II levels are normal.

Effects of vasoactive agents on isolated human umbilical arteries and veins

Abstract: ALTURA, BURTON M., D. MALAVIYA, CHARLES F. REICH, AND LOUIS R. ORKIN. Effects of vasoactive agents on isolated human umbilical arteries and veins. Am. J. Physiol. 222(Z): 345-355. 1972.In vitro experiments, using both helically and longitudinally cut human umbilical arteries and veins (HUAV), were designed to determine: I) whether any of the known circulating vasoactive substances can induce contraction of these vessels in low (physiologic?) concentrations; 2) the relative potency of these substances; 3) the existence of specific drug receptors which subserve contraction; and 4) the relative contribution each type of smooth muscle layer (i.e., longitudinal vs. circular) may play in response to vasoactive agents and in development of spontaneous mechanical activity. The results indicate : 1) 10 different vasoactive agents (amines, polypeptides, prostaglandins, and potassium ions) induce varying degrees of unequal contractile responses (serotonin = maximum); 2) only serotonin (

Calcitonin Receptors of Kidney and Bone

Abstract: Receptors for calcitonin, determined by activation of adenylate cyclase, were found in a distribution among zones of the kidney distinct from that of receptors for parathyroid hormone or vasopressin Competitive binding studies showed that the receptors for calcitonin are similar in kidney and bone and that their high apparent affinity for salmon calcitonin accounts in part for the high biological potency in vivo of salmon calcitonin

Receptors for complement and immunoglobulin on human leukemic cells and human lymphoblastoid cell lines.

Abstract: The bone marrow-derived (B) lymphocyte can be identified by the presence of easily detectable surface immunoglobulin and a receptor for antigen-antibody-complement complexes (EAC'). Monocytes and macrophages also bear a receptor for EAC' and in addition possess a receptor for red cell-IgG complexes (EA). Thymus-derived (T) lymphocytes bear neither of these receptors. The cells of 15 patients with leukemia and 19 human lymphoblastoid cell lines were examined for the presence of the EAC' and EA receptors. Of the human leukemias studied, only the cells from the patients with chronic lymphatic leukemia (CLL) possess the EAC' receptor. The EA receptor could not be demonstrated on CLL cells; hence, CLL cells bear the lymphocyte EAC' receptor and by this criteria represent B lymphocytes. 12/19 of the cell lines studied could be classified as B lymphocytes by the presence of the EAC' receptor and absence of the EA receptor. 2/19 cell lines possessed both the EAC' and EA receptors and thus resemble the monocyte. 5/19 cell lines had no detectable receptor for EAC' or EA. The approach presented in this study for the classification of leukemias and cell lines as to their B lymphocyte, T lymphocyte, or monocyte origin may have useful diagnostic and therapeutic implications.

Evidence for a Primary Association between Immunoblasts and Small Gut

Abstract: SINCE the observations of Gowans and Knight1 it has been shown that many of the lymphoid blast cells (immunoblasts) that appear in the thoracic duct lymph of rats after immunization of the caudal lymph nodes with a variety of antigens “home” to the lamina propria of the small gut2, where they differentiate into plasma cells3. The immunological specificity of the immunoblasts, however, does not seem to affect their affinity for the small gut2,3. Recent work4 has shown that immunoblasts home just as readily to the small gut of unsuckled, neonatal rats obtained by Caesarian section, in which the gut is sterile and presumably antigen-free, and where there is no influence of endogenous or maternal colostral immunoglobulins. The entry of immunoblasts into the lamina propria must involve the transmigration of these cells across the vascular endothelium. The first event in such a process may be the engagement of a receptor on the surface of the immunoblast with a complementary group on its endothelial surface. We have studied the entry of immunoblasts into “free” grafts of syngeneic foetal gut, implanted subcutaneously, and the entry of xenogeneic immunoblasts into normally situated gut.

Target tissue receptors for progesterone: the influence of estrogen treatment.

Abstract: The effects of estrogen treatment on the specific progesterone binding protein (receptor) in the chick oviduct were investigated. The progesterone receptor is present in non-estrogen treated oviducts but the tissue concentration of this protein increases several fold during a 2- week-period of estrogen treatment. In addition, qualitative changes in the receptor protein are indicated by its sedimentation properties on sucrose gradients. Following estrogen treatment, the 4-5S progesterone-receptor complex is apparently altered to a form which sediments in the 6-8S region on sucrose gradients. These results suggest that the enhanced responsiveness of the oviduct to progesterone following estrogen treatment may arise through quantitative and qualitative changes in progesterone receptor molecules. (Endocrinology 90: 1041, 1972)

A functional analysis of the components of the mesencephalic nucleus of the fifth nerve in the cat

Abstract: 1. The mesencephalic nucleus of the trigeminal nerve has been studied using extracellular micro-electrode recording and the constituent cell types identified. 2. Two types of unit were found, namely, muscle spindle first order afferents of ipsilateral jaw-closing muscles and mechanoreceptor afferents of ipsilateral maxillary and mandibular teeth. 3. No evidence was found for representation of extra-ocular muscle stretch receptors, of temporo-mandibular joint receptors or of tendon organs of jaw muscles. 4. Spindle units of each of the jaw-closing muscles were recorded in all parts of the nucleus and there was no evidence of their segregation according to muscle of origin. 5. Attempts to classify spindle units by their dynamic response to ramp stretches, their following of high frequency vibration and their interspike interval variability at constant length gave no indication of two populations when fusimotor activity was suppressed. 6. Following the injection of suxamethonium, however, units fell into two groups according to their dynamic index. Their behaviour resembled that described for primary and secondary spindle afferents. In data pooled from all of the jaw-closing muscles there were approximately equal numbers of units in each group.

Acetylcholine receptors: number and distribution at neuromuscular junctions in rat diaphragm.

Abstract: The number of acetylcholine receptors per motor end plate in the rat diaphragm, measured by the binding of [(125)1]alpha-bungarotoxin, varies directly with rat size and is (4.0 +/- 0.2) x 10(7) for full-grown male rats. Autoradiographic analysis of single fibers labeled with this substance reveals that virtually all of these receptors are localized in the end plate.

Radioligand-Receptor Assay of Luteinizing Hormone and Chorionic Gonadotropin

Abstract: The specific binding of labeled gonadotropin to subcellular fractions of the rat testis has been utilized in the development of a sensitive radioligand assay system for LH and HCG. The cell-free supernatant of the fragmented interstitial cell fraction was found to contain high affinity gonadotropin receptors, which showed rapid and specifically reversible binding of 125I-labeled LH and HCG. For binding assays, satisfactory results were also obtained with the fraction prepared by centrifugation at 1500 g after homogenization of the whole testis. Assays were performed by incubation of tracer hormone with standards or samples and binding fraction for 2 hr at 37 C, or 16 hr at 24 C. Separation of bound and free tracer was performed by centrifugation and washing of the particulate receptor fraction, followed by measurement of the bound radioactivity. Parallel dose-response curves were obtained with human pituitary LH (LER 907), human urinary LH, and human chorionic gonadotropin, while ovine, bovine, and rat LH...