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PubMed1981

Autoantibodies to insulin receptors.

In summary, these studies using antibodies to the insulin receptor have provided some new insights into the structure of the insulin receptor and the action of insulin itself. They suggest that most of insulin's actions are mediated through a common pathway and these can be initiated by interaction of ligands other than insulin with the insulin receptor. These include the entire spectrum of metabolic effects (both acute and chronic). Receptor occupancy alone is not sufficient for signal generation. Both insulin and anti-receptor antibody induce receptor aggregation which appears to be required for activity. And finally, although both insulin and anti-receptor antibody are internalized, there is no evidence to suggest that this is important in their action. The growth effect of insulin appears to be mediated via a different pathway.

Adipose Tissue↗
PubMed1998

Human sperm non-nuclear progesterone receptor expression is a novel marker for fertilization outcome.

In a prospective, blind study, we have examined the relationship among the expression of human sperm surface progesterone receptors, the ability to undergo a mannose-stimulated acrosome reaction and the rate of fertilization in vitro. Individual aliquots of motile spermatozoa were surface-labelled with progesterone and/or mannose-fluoresceinated ligands. Spontaneous acrosome loss and the increase in acrosome reactions following exposure of spermatozoa to mannose ligands were assessed using rhodaminated Pisum sativum agglutinin. Progesterone fluoresceinated ligand binding was observed to occur in two patterns: (i) a uniform distribution of labelling over the acrosome cap (pattern II), and (ii) labelling limited to the equatorial and postacrosomal regions of the human sperm head (pattern III). A conversion of pattern II to pattern III binding was observed and was associated with the acrosome reaction. Pattern III binding was highly correlated with both fertilization potential and the ability to undergo a mannose-stimulated acrosome reaction (P < 0.001). In contrast, normal sperm mannose receptor expression was seen in five men whose abnormal progesterone receptor expression/function and inability to acrosome react after mannose treatment were correlated with their reduced fertility in vitro. In conclusion, surface progesterone receptor aggregation enhances the mannose ligand-stimulated acrosome reaction. Such detection of defective sperm surface progesterone receptor expression/function may be useful in the evaluation and management of male infertility.

Acrosome↗
PubMed1989

Formation of acetylcholine receptor clusters in chick myotubes: migration or new insertion?

Experiments were performed to study the feasibility of two mechanisms of acetylcholine receptor (ACHR) accumulation in chick myotubes: diffusion and trapping of previously dispersed surface receptors and localized insertion of new receptors at accumulation sites. Fluorescence photobleaching recovery (FPR) measurements indicated that the majority of diffusely distributed ACHRs in chick myotube membranes were mobile whereas nearly all receptors within high density clusters were effectively immobile. Unlike previous reports, two rates of ACHR movement characterized the mobile population. Moreover, we found that the estimated diffusion coefficient depended critically on the objective (spot size) used to assay recovery from bleaching. Implications of this finding for mechanisms of receptor immobilization are discussed. Extracts of chick brain, known to increase the number of surface receptors, did not alter receptor mobility. Extracts of Torpedo electric organ that increase the number of receptor aggregates, decreased the mobile fraction of ACHRs. Simulations of the diffusion and trapping mechanism indicated that captured receptors should congregate around the periphery of a receptor patch during the first hour after they were inserted into the membrane. However, newly inserted ACHRs were found to be located centrally within receptor patches under neurites, and this was not consistent with an exclusive diffusion-trapping mechanism. We also studied the mobility of ACHRs near points of contact made by cholinergic growth cones. The rate of receptor movement was increased in the vicinity of growth cones, but the magnitude of this effect was small.

Animals↗
PubMed1977

Nerve-induced and spontaneous redistribution of acetylcholine receptors on cultured muscle cells.

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.

Animals↗
PubMed1995

Solubilization of receptors for pancreatic polypeptide from rat liver membranes.

We have previously identified, on rat liver microsomes and plasma membranes, proteins that bind pancreatic polypeptide (PP) with high affinity and specificity and that may serve as receptors for a hepatic effect of PP (J. Biol. Chem. 267: 9416-9421, 1992). Further characterization of these proteins requires the solubilization of receptors with conserved ability to bind PP selectively and efficiently. In this report, using 6 mM of the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS), we solubilized, from liver microsomes, receptors that bound PP with high affinity (dissociation constant 6.15 +/- 1.6 nM) and specificity (no interaction with the homologous peptides neuropeptide Y and peptide YY). Gel filtration chromatography showed different degrees of receptor aggregation related to different concentrations of CHAPS in the eluent. To characterize the structure of these solubilized receptors, the chemical cross-linker N-(5-azido-2-nitrobenzoyloxy)succinimide was used to covalently bind these receptors to radiolabeled PP, and the resulting PP-receptor complexes were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A radioactive band with an apparent molecular weight (M(r)) of 46,000 was detected that was inhibited by unlabeled PP with a half-maximal inhibitory concentration of approximately 10(-8) M. It most likely reflected a PP receptor with an estimated M(r) of 42,000, excluding the molecular weight of PP. The migration of this complex was not affected by the reducing agent dithiothreitol, suggesting the absence of disulfide bonding. The solubilization and identification of a bioactive hepatic PP receptor will allow further characterization and purification of this receptor and will lead to the clarification of the interaction between PP and the digestive system.

Animals↗
PubMed1983

Induction of acetylcholine receptor synthesis and aggregation: partial purification of low-molecular-weight activity.

We have studied the effect of saline and acid extracts of chick brain on the total number of acetylcholine (ACh) receptors and the number of receptor clusters in cultured chick muscle cells. Myotubes in 7-day cultures responded more rapidly to brain extract than did myotubes in 4-day cultures, so the older cells were used in subsequent bioassays. A large percentage of the receptor inducing activity was soluble in 2% trifluoroacetic acid (TFA), and this material appeared by Sephadex G-25 chromatography to be about 1000 daltons in size. Activity was retained on octadecasilyl silica and was further purified by reverse-phase high-pressure liquid chromatography using a TFA-acetonitrile gradient system. Material that eluted between 35 and 40% acetonitrile, termed C4018, was 500- to 1000-fold more potent than saline extract. The receptor accumulation induced by C4018 was associated with an increased rate of receptor incorporation, presumably receptor synthesis, rather than to a decrease in receptor degradation. An increase in incorporation was detected as early as 3 hr after C4018 was added to 7-day cultures and the effect was maximal after 10 hr. C4018 also promoted the aggregation of receptors that were already incorporated in the surface membrane at the time to addition. It is not yet known if aggregation of "old" receptors and increased receptor synthesis are related or if the two phenomena are mediated by the same molecule.

Acetonitriles↗
PubMed1981

Alterations in the number and affinity of junctional acetylcholine receptors in a myopathy with tubular aggregates. A newly recognized receptor defect.

This paper reports the findings in a 32-year-old man who presented in adult life with a myasthenic syndrome characterized by dysphagia, dysphonia, fluctuating ptosis, episodic diplopia and a variable weakness of the limbs and trunk. Electromyography showed a small decremental response, increased neuromuscular jitter and blocking of some components. Histochemical and electron microscopic studies revealed changes in end-plate morphology and prominent tubular aggregations within the muscle fibres. Radiochemical investigations using di-iodinated 125I-alpha-bungarotoxin demonstrated a reduction in the number of AChR and alterations in receptor affinity which suggested an abnormality of the AChR macromolecule.

Adult↗
PubMed1996

Reconstitution of T cell receptor signaling in ZAP-70-deficient cells by retroviral transduction of the ZAP-70 gene.

A variant of severe combined immunodeficiency syndrome (SCID) with a selective inability to produce CD8 single positive T cells and a signal transduction defect in peripheral CD4+ cells has recently been shown to be the result of mutations in the ZAP-70 gene. T cell receptor (TCR) signaling requires the association of the ZAP-70 protein tyrosine kinase with the TCR complex. Human T cell leukemia virus type I-transformed CD4+ T cell lines were established from ZAP-70-deficient patients and normal controls. ZAP-70 was expressed and appropriately phosphorylated in normal T cell lines after TCR engagement, but was not detected in T cell lines from ZAP-70-deficient patients. To determine whether signaling could be reconstituted, wild-type ZAP-70 was introduced into deficient cells with a ZAP-70 retroviral vector. High titer producer clones expressing ZAP-70 were generated in the Gibbon ape leukemia virus packaging line PG13. After transduction, ZAP-70 was detected at levels equivalent to those observed in normal cells, and was appropriately phosphorylated on tyrosine after receptor engagement. The kinase activity of ZAP-70 in the reconstituted cells was also appropriately upregulated by receptor aggregation. Moreover, normal and transduced cells, but not ZAP-70-deficient cells, were able to mobilize calcium after receptor ligation, indicating that proximal TCR signaling was reconstituted. These results indicate that this form of SCID may be corrected by gene therapy.

CD4-Positive T-Lymphocytes↗
PubMed1991

The action of luteinizing hormone on the testis.

Luteinizing hormone (LH) and human chorionic gonadotrophin (hCG) receptors are coupled to intracellular effector systems, most notably adenylate cyclase, through guanyl nucleotide-binding proteins or G-proteins. The molecular mechanism involved in the dynamic coupling of the LH/hCG receptor however, are not known. It has been postulated that receptor aggregation at the molecular level plays a critical role in this process. There have been attempts to understand the receptor association and dissociation phenomena at the molecular level. One of them involves the participation of the major histocompatibility complex (MHC) class I antigen in the mechanism of receptor activation and/or expression. One molecular basis for these mechanisms consists of a physical interaction between MHC proteins and receptors to form "compound receptors" able to transfer a hormonal signal to the cell. Using a photo-reactive probe we demonstrated that the LH/hCG receptors and the class I antigens are closely associated in the membrane. Thus, it is possible to form covalent complexes of hCG and class I antigens through the binding of the hormone to specific receptors. These findings imply that LH/hCG receptors and the MHC class I antigens may interact at the level of the plasma membrane in the mechanism of LH action. We also performed experiments using a single cell and limiting stimulation to a patch of membrane. The results stimulating the cell in a localized area suggested that even if all components are entirely free to float there is a constraint in the localization of the receptor, G-protein, and/or the effector, supporting the constraint dissociation model. Within a limited area subunits could dissociate, but they would not be free to diffuse throughout the membrane. Moreover the concept of compartmentalization that has been utilized to explain some inconsistencies in second-messenger action now can be proved by experimental design.

Animals↗
PubMed1997

A single STAT recruitment module in a chimeric cytokine receptor complex is sufficient for STAT activation.

We established a system of receptor chimeras that enabled us to induce heterodimerization of different cytoplasmic tails. Fusion constructs were created that are composed of the extracellular parts of the interleukin-5 receptor alpha and beta chains, respectively, and the transmembrane and intracellular parts of gp130, the signal transducing chain of the interleukin-6 receptor complex. In COS-7 transfectants we observed a dose-dependent interleukin-5-inducible STAT1 activation for which the presence of both the alpha and the beta chain chimera was needed. No STAT activity was detected if one of the cytoplasmic tails of the receptor complex was deleted, indicating that STAT activity resulted from a receptor dimer rather than from higher receptor aggregates. We further investigated whether dimerization of STAT1 depends on the juxtaposition of two STAT recruitment modules in a receptor complex. We show that a receptor dimer with only a single STAT1 docking site was still able to lead to STAT1 activation. This indicates that the formation of a paired set of STAT binding sites in a receptor complex is not the prerequisite for STAT factor dimerization. Our findings are discussed in view of alternative STAT dimerization models.

Animals↗
PubMed1980

Cultured hepatoma cells as a model system for studying insulin processing and biologic responsiveness.

Monolayer cultures of minimal deviation hepatoma cells (H4-II-E-C3') bound and degraded insulin specifically, the apparent Ki value for insulin inhibition of both processes being 1 x 10(-8) M, indicating that cell-bound 125I-insulin is the substrate for subsequent hormone degradation in these cells as in isolated hepatocytes.1 The time course of insulin binding to its receptor depended on hormone concentration and temperature. Degradation of insulin also depended highly on temperature, with little or no degradation occurring at less than 20 degrees C, a temperature below which a membrane-lipid phase transition may block homone translocation or uptake. The effects of various agents on the binding and degradation of 125I-insulin also were tested. Agents believed to inhibit intralysosomal degradation of various proteins also inhibited the degradation of 125I-insulin by H4 cells (chloroquine, ammonium chloride, procaine, and lidocaine); inhibitors of energy production (dinitrophenol, sodium cyanide) inhibited degradation; an agent which inhibits microtubule function (vinblastine) blocked insulin degradation; and methylamine, reported to prevent receptor aggregation,2 also interfered with insulin processing. These findings are consistent with a model for cellular insulin processing, comprising receptor binding, clustering of receptors, endocytotic uptake, intralysosomal degradation, and extracellular release of some degradation products. H4 cells were highly sensitive to insulin. The KE for a half-maximal response of hormone-stimulated incorporationof 14C-glucose into glycogen was 10(-11) M insulin, corresponding to less than 1% receptor occupancy. This response was also mimicked by concanavalin A at a concentration of 10 microgram/ml. Vinblastine and chloroquine both significantly inhibited insulin-stimulated glucose incorporation into glycogen without affecting basal levels. However, since these inhibitory effects were not relieved by addition of excess insulin, it seems unlikely that their action on glycogen synthesis was exerted only at the level of the generation of an active intermediate or degradation product from hormone-receptor complexes. The hormone-sensitive H4 cells thus provide a useful system for further studies examining the role of insulin-receptor uptake in hormone action, receptor regulation, and signal termination.

Animals↗
PubMed2000

Platelet function during cardiopulmonary bypass not changed by two different doses of aprotinin.

BACKGROUND AND OBJECTIVE: Bleeding is one of the major complications of cardiopulmonary bypass (CBP) during cardiac surgery. A platelet function defect seems to be the main cause of the hemostatic problems associated with CBP. Controversial results have been reported concerning the possible protective mechanism of action of aprotinin on platelets. DESIGN AND METHODS: In this study we investigated the effect of two different dosages of aprotinin (high and pump-prime-only dose) on platelet reactivity in vitro and adhesion, activation and aggregation receptors on the platelet surface. RESULTS: The results obtained from 53 patients undergoing CBP showed a significantly deficient platelet aggregation in response to agonist in all groups without differences between aprotinin treated or not treated patients. No changes in platelet surface expression of glycoprotein (GP) IIb-IIIa, GPIb, GPIV and P-selectin, were observed during CBP between patients treated with aprotinin or not. INTERPRETATION AND CONCLUSIONS: These data suggest that inadequate platelet function induced by CBP is not a defect intrinsic to the platelet. We conclude that the hemostatic effect of aprotinin, regardless of the dose employed, is not mediated by protection of platelet function.

Adult↗
PubMed2001

Schwann cells express active agrin and enhance aggregation of acetylcholine receptors on muscle fibers.

To explore novel roles of glial cells in synaptic function and formation, we examined the expression of agrin in frog Schwann cells and tested their role in the aggregation of acetylcholine receptors (AChRs). Using reverse transcription-PCR, we found that Schwann cells along nerve fibers in tadpoles expressed only the inactive agrin isoform B0 but began to also express active agrin isoforms B11 and B19 at approximately metamorphosis. During nerve regeneration in the adult, the expression of these active agrin isoforms in Schwann cells was upregulated, including the appearance of the most potent isoform, B8. This upregulation was induced by regenerating axons but not by nerve injury per se. In muscle cultures, the presence of adult Schwann cells enhanced the number and the total area of AChR aggregates 2.2- and 4.5-fold, respectively, and this enhancement was eliminated by heparin treatment. Furthermore, adult Schwann cells in culture expressed active agrin isoforms and produced agrin protein. Using a novel technique to selectively ablate perisynaptic Schwann cells (PSCs) at the neuromuscular junction, we found that PSCs also expressed active agrin isoforms B11 and B19, and these active isoforms were upregulated, including the appearance of B8, during reinnervation. Observation in vivo showed that extrajunctional AChR aggregates were associated with PSC sprouts after nerve injury and subsequent reinnervation. These results suggest that, contrary to the prevailing view that only neurons express active agrin, glial cells also express active agrin and play a role in the aggregation of AChRs both in vitro and in vivo.

Agrin↗
PubMed1984

Binding kinetics of PAF-acether (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) to intact human platelets.

The binding of [3H]PAF-acether (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) to intact human gel-filtered platelets was measured at 22 degrees C. Specific binding reached saturation within 15 min at high doses of [3H]PAF-acether (0.5-0.9 nM), whereas about 90 min were required when low doses (0.02-0.5 nM) were used. Above 1 nM, [3H]PAF-acether non-specific binding increased progressively, which together with the demonstration of a 3H-labelled metabolite suggested uptake and metabolism of [3H]PAF-acether. Equilibrium analysis revealed one class of specific receptors with a Ka of 18.86 +/- 4.82 X 10(9) M-1 and 242 +/- 64 binding sites per platelet. Non-equilibrium binding revealed a similar Ka (16.87 X 10(9) M-1). Specific binding became irreversible after prolonged incubation, a process that was enhanced at increasing concentrations of [3H]PAF-acether. Platelets made desensitized to PAF-acether by prior incubation with unlabelled PAF-acether failed to bind a second dose of PAF-acether (3H-labelled), suggesting that desensitization resulted from loss of available binding sites. Under the conditions of the binding studies, PAF-acether induced exposure of the fibrinogen receptor, aggregation (in a stirred suspension) and alterations in (poly)-phosphatidylinositides. These results suggest that PAF-acether initiates platelet responses via receptor-mediated processes.

Adrenergic alpha-Antagonists↗
PubMed1988

Calcium specificity of the antigen-induced channels in rat basophilic leukemia cells.

Ion channels, activated upon IgE-Fc epsilon receptor aggregation by specific antigen, were studied in micropipet-supported lipid bilayers. These bilayers were reconstituted with purified IgE-Fc epsilon receptor complex and the intact 110-kDa channel-forming protein, both isolated from plasma membranes of rat basophilic leukemia cells (line RBL-2H3). In order to identify the current carrier through these ion channels and to determine their ion selectivity, we investigated the currents flowing through the IgE-Fc epsilon receptor gated channels in the presence of a gradient of Ca2+ ions. Thus, the solution in which the micropipet-supported bilayer was immersed contained 1.8 mM CaCl2, while the interior of the micropipet contained 0.1 microM Ca2+ (buffered with EGTA). Both solutions also contained 150 mM of a monovalent cation chloride salt (either K+ or Na+). The currents induced upon specific aggregation of the IgE (by either antigen or anti-IgE antibodies) were examined over a range of potentials imposed on the bilayer. The type of conductance event most frequently observed under the employed experimental conditions was a channel that has a slope conductance of 3 pS and a reversal potential practically identical with the calculated value for the reversal potential of calcium (134 +/- 11 mV in the presence of sodium, 125 +/- 13 mV in the presence of potassium). These results indicate that this channel is highly selective for calcium against the monovalent cations sodium and potassium. This same channel has a conductance of 4-5 pS in the presence of symmetrical solutions containing only 100 mM CaCl2 and 8 pS in the presence of 0.5 M NaCl with no calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Evidence for two distinct phosphorylation pathways activated by high affinity immunoglobulin E receptors.

The high affinity receptor for immunoglobulin (Ig) E on mast cells, along with the antigen receptors on T and B cells and Fc receptors for IgG, belongs to a class of receptors which lack intrinsic kinase activity, but activate non-receptor tyrosine and serine/threonine kinases. Receptor engagement triggers a chain of signaling events leading from protein phosphorylation to activation of phosphatidylinositol-specific phospholipase C, an increase in intracellular calcium levels, and ultimately the activation of more specialized functions. IgE receptor disengagement leads to reversal of phosphorylation by undefined phosphatases and to inhibition of activation pathways. Here we show that phenylarsine oxide, a chemical which reacts with thiol groups and has been reported to inhibit tyrosine phosphatases, uncouples the IgE receptor-mediated phosphorylation signal from activation of phosphatidyl inositol metabolism, the increase in intracellular calcium levels, and serotonin release. Phenylarsine oxide inhibits neither the kinases (tyrosine and serine/threonine) phosphorylating the receptor and various cellular substrates nor, unexpectedly, the phosphatases responsible for the dephosphorylation following receptor disengagement. By contrast, it abolishes the receptor-mediated phosphorylation of phospholipase C-gamma 1, but not phospholipase C activity in vitro. Therefore the phosphorylation and activation of phospholipase C likely requires a phenylarsine oxide-sensitive element. Receptor aggregation thus activates at least two distinct phosphorylation pathways: a phenylarsine oxide-insensitive pathway leading to phosphorylation/dephosphorylation of the receptor and of various substrates and a sensitive pathway leading to phospholipase C-gamma 1 phosphorylation.

Animals↗
PubMed1982

Epidermal growth factor: uptake and fate.

Lateral diffusion of epidermal growth factor (EGF) receptors along the plane of the cell membrane can be measured using fluorescently labelled analogues of EGF and the fluorescence photobleaching recovery method in cultured cells. With the aid of high image-intensified fluorescent microscopy, the receptors, which are initially distributed diffusely, form patches and undergo endocytosis at 37 degrees C. These gross processes may not be critical in mediating the initial, rapid actions of the hormone. The processes of uptake and endocytosis correspond biochemically to the loss of surface receptors ('down-regulation') and degradation of the receptor and hormone via lysosomes. The EGF receptors are not apparently recycled or re-utilized, and they are continuously internalized, even in the absence of ligand. Since all manoeuvres that interfere with intracellular degradation or processing block mitogenesis, it is proposed that one or both of these may be essential processes, although in such a case they must be continuous and protracted functions. Slow nuclear accumulation of the complex of hormone and receptor may be an important process. In addition, evidence suggests that limited (submicroscopic) receptor aggregation (dimerization) at the cell surface may be necessary and sufficient to trigger the long-term effects (but not the immediate effects), and thus this aggregation may be required for endocytosis. The ligand itself may not be an essential structural component of the action of the receptor since anti-receptor antibodies can elicit mitogenic responses. Recent results suggest that EGF receptors normally exist in a low affinity state which is rapidly converted by EGF (at 37 degrees C but not at 4 degrees C) to a high affinity state by a process that requires prior intact protein synthesis. Furthermore, the accumulation of a special, stable intracellular pool of the complex may be related to the control of cellular growth (and tumour promotion).

Animals↗
PubMedDate not supplied

Changes in net charge of glucocorticoid receptors by activation, and evidence for a biphasic activation kinetics.

The kinetics of glucocorticoid receptor activation and the changes in molecular properties of the receptors by the activation were studied, employing aqueous two-phase partitioning of rat thymocyte, rat liver and mouse S49.1 lymphoma cell cytosol labelled with tritiated glucocorticoid. By a mathematical analysis of the time-course of the receptor partition coefficient during activation, we demonstrate that at least two different receptor conversions take place during this process. Partitionings at conditions excluding receptor aggregation allowed an evaluation of differences in net charge between activated and non-activated forms of native and chymotrypsin-treated receptors. The net charge of the chymotrypsinized receptor changes little by the activation, being between 0 and -10 at pH 8 both in the non-activated and the activated state. In contrast, the activation changes the net charge of the native receptor from around -50 to around -10.

Animals↗