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PubMed2001

Slow switching in globally coupled oscillators: robustness and occurrence through delayed coupling.

The phenomenon of slow switching in populations of globally coupled oscillators is discussed. This characteristic collective dynamics, which was first discovered in a particular class of the phase oscillator model, is a result of the formation of a heteroclinic loop connecting a pair of clustered states of the population. We argue that the same behavior can arise in a wider class of oscillator models with the amplitude degree of freedom. We also argue how such heteroclinic loops arise inevitably and persist robustly in a homogeneous population of globally coupled oscillators. Although a heteroclinic loop might seem to arise only exceptionally, we find that it appears rather easily by introducing time delay into a population which would otherwise exhibit perfect phase synchrony. We argue that the appearance of the heteroclinic loop induced by the delayed coupling is then characterized by transcritical and saddle-node bifurcations. Slow switching arises when a system with a heteroclinic loop is weakly perturbed. This will be demonstrated with a vector model by applying weak noises. Other types of weak symmetry-breaking perturbations can also cause slow switching.

Journal Article↗

PubMed2004

Electron-phonon coupling and a polaron in the t-J model: from the weak to the strong coupling regime.

We present numeric results for ground state and angle resolved photoemission spectra (ARPES) for a single hole in the t-J model coupled to optical phonons. The systematic-error-free diagrammatic Monte Carlo method is employed where the Feynman graphs for the Matsubara Green function in imaginary time are summed up completely with respect to phonon variables, while magnetic variables are subjected to the noncrossing approximation. We obtain that at electron-phonon coupling constants relevant for high T(c) cuprates the polaron undergoes a self-trapping crossover to the strong-coupling limit and theoretical ARPES demonstrate features observed in experiment: A broad peak in the bottom of the spectra has momentum dependence which coincides with that of a hole in the pure t-J model.

Journal Article↗

PubMed1996

Geometric approach for coupling enhancement of magnetically coupled coils.

This paper presents a geometric approach for the enhancement of the coupling coefficient between two magnetically coupled coils. It is demonstrated that the coupling coefficient can be considerably enhanced, if the turns of the coils are not concentrated at the circumferences, but distributed across the diameters. For analysis, each of the two coils is assumed to be composed of concentric circular loops. The experimental results are in very good agreement with the theoretical results.

Equipment Design↗

PubMed1980

Multi-level couple therapy: applying a metacommunicational framework of couple interactions.

Excerpts from a couple therapy case are cited to illustrate the practical significance of a multi-level framework in understanding couple interactions. The clinical implications of the metacommunicational framework, as a metaphor for examining and understanding relational processes, are discussed. Also, the pragmatics of following "process" at a variety of levels when working with punctuational differences, developing therapy strategies and goals, and measuring the progress of couple therapy are discussed.

Accidents↗

PubMed1984

Propagation through electrically coupled cells: two inhomogeneously coupled cardiac tissue layers.

Most of the ventricular endocardial surface is covered with a layer of Purkinje (P) cells which provide a rapid spread of activation into the underlying ventricular (V) cells. We have shown experimentally that the P-V junctional region of papillary muscles is spatially inhomogeneous with different regions showing bidirectional conduction, bidirectional block, or unidirectional block between the P and V layers. We have now extended our one-dimensional simulations to a double layer of excitable cells with spatially inhomogeneous electrical coupling between the two layers. Our simulations show that a partial uncoupling can actually increase the common conduction velocity of the two layers and can produce successful P-to-V conduction at regions that would otherwise show P-to-V block, and inhomogeneous spatial distributions of coupling resistivity between two excitable layers can simulate the observed spatial distribution of spatially variable conduction block in papillary muscles. Our simulations indicate that a partial regional electrical coupling may be a useful design feature of the heart to enhance the velocity and safety factor of ventricular activation, but the further increases in uncoupling that may be associated with ischemia may provide a structural basis for the occurrence of arrhythmias.

Action Potentials↗

PubMed2003

[Cooperation of two subtypes of PGE2 receptor, Gi coupled EP3 and Gs coupled EP2 or EP4 subtype].

Four prostaglandin E (EP) receptor subtypes have been identified and cloned, designated as EP1, EP2, EP3 and EP4. These EP receptors are members of the G-protein coupled receptor family. EP3 receptor signals are primarily involved in inhibition of adenylyl cyclase via Gi activation, while EP2 and EP4 receptor signals cause a stimulation of adenylyl cyclase via Gs activation. Immune cells, such as mast cells, express multiple EP subtypes on their cell membranes, but few studies have been conducted to understand exactly what signals the main flow for the multiple subtypes expressing immune cells. We previously demonstrated that activation of Gi-coupled EP3 receptor exhibited a cooperative effect on cAMP synthesis induced by Gs-coupled EP2 receptor in COS-7 cells. Here we report that a selective EP4 agonist-induced adenylyl cyclase activity was augmented by simultaneous addition of a selective EP3 agonist in mastocytoma P-815 cells, which express mRNAs for both EP3 and EP4 subtypes. The augmentation in cAMP synthesis was found to be pertussis toxin-sensitive. P-815 cells are demonstrated to bind to Pronectin-F, a proteolytic fragment of fibronectin, in adhesion protein of the extracellular matrix, by addition of PGE2, which is mediated by PKA. The binding of P-815 cells to Pronectin-F mediated by EP4 receptor was augmented by the EP3 receptor. These findings indicate that two subtypes of PGE2 receptors, EP3 and EP4, cooperatively activate the cAMP-mediated adhesion event through induction of fibronectin ligand elicited by PGE2 in P-815 cells. Furthermore, the PGE2-induced adhesion response may contribute to the mast cell recruitment function on extracellular matrix during inflammation.

Adenylyl Cyclases↗

PubMed2002

Coupling-loss reduction of a vertically coupled microring resonator filter by spot-size-matched busline waveguides.

To improve the input-output coupling loss of a vertically coupled microring resonator filter, we fabricated microring resonators on an antiresonant reflecting optical waveguide (ARROW) with a large spot size and on the rectangular busline waveguide with a spot-size transformer. The spot size and the tapered structure were optimally designed from the viewpoint of spot-size matching to single-mode fibers and the reduction of radiation loss. Clear dropping responses were demonstrated for the ARROW-based microring resonator filters, and the coupling loss was successfully reduced by 22 dB.

Journal Article↗

PubMed1999

Effect of volatile anaesthetics on the electrical activity and the coupling coefficient of weakly electrically coupled neurones.

1. The application of the volatile anaesthetics, halothane and isoflurane (1% v/v and 2% v/v), to the CNS of Lymnaea reduced the firing frequency of the small weakly coupled pedal A cluster (PeA) neurones, which eventually become quiescent. There was no change in their resting membrane potential. 2. Met-enkephalin significantly increased the coupling coefficient between PeA neurones. 3. The volatile anaesthetics decreased the coupling coefficient even in the presence of met-enkephalin. 4. These effects were dose dependent and the effects of halothane were more rapid than those of isoflurane, reflecting their different anaesthetic potencies.

Anesthetics, Inhalation↗

PubMed1992

Factors determining the specificity of signal transduction by guanine nucleotide-binding protein-coupled receptors. II. Preferential coupling of the alpha 2C-adrenergic receptor to the guanine nucleotide-binding protein, Go.

Cell to cell communication by many hormones and neurotransmitters involves three major entities: receptor (R), G-protein (G), and effector molecule (E). Plasticity in this system is conferred by the existence of each entity as isoforms or closely related subtypes that are expressed in a tissue-specific and developmentally regulated manner. Factors that determine signal specificity in this system are poorly understood. Such factors include the relative affinity and stoichiometry of R-G or G-E and the possible colocalization of R-G-E in cellular microdomains. Utilizing the alpha 2-adrenergic receptor (alpha 2-AR) system as a representative subfamily of this class of signal transducers, we determined the relative importance of these factors. By analysis of R-G coupling in mammalian cells cotransfected with alpha 2-AR genes and G alpha cDNA, we demonstrate preferential coupling between an alpha 2-AR subtype and Go. Our data implicate R-G affinity as an important determinant of signal transduction specificity and indicate that a critical level of Go alpha is required for coupling. This report indicates the utility of R-G cotransfection in mammalian cells as a "natural environment model" to characterize events occurring at the R-G and G-E interface.

3T3 Cells↗

PubMed1992

Factors determining the specificity of signal transduction by guanine nucleotide-binding protein-coupled receptors. III. Coupling of alpha 2-adrenergic receptor subtypes in a cell type-specific manner.

A number of diverse signaling pathways can be activated by G-protein coupled receptors. However, the factors involved in selection of a particular transduction pathway by a single receptor are not well understood. We are attempting to address this issue utilizing the alpha 2-adrenergic receptor (alpha 2-AR) subfamily as a representative model system. In this report, we demonstrate that the cellular response mediated by an alpha 2-AR subtype is cell-specific and thus depends on its environment. Receptor coupling to adenylylcyclase was determined following stable expression of the rat alpha 2B- and alpha 2D-AR subtypes in three functionally distinct cell types (NIH-3T3 fibroblasts, DDT1 MF-2 smooth muscle cells, and the pheochromocytoma cell line PC-12). When the receptor subtype gene is expressed in NIH-3T3 and DDT1 MF-2 cells, receptor activation inhibits basal and forskolin-induced increases in cellular cAMP. However, in PC-12 transfectants the same receptor subtype actually increases basal cAMP and augments the effect of forskolin. Potentiation of the forskolin effect in PC-12 cells is insensitive to pertussis toxin but is blocked by loading the cells with BAPTA (bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid) which minimizes changes in Ca2+i by calcium chelation. These data and the functional demonstration of a Ca2+/calmodulin-sensitive adenylylcyclase in PC-12 but not NIH-3T3 and DDT1 MF-2 cells, suggests that the cell-specific effects of epinephrine are due to receptor coupling to both different G-proteins and types of adenylylcyclase.

3T3 Cells↗

PubMedDate not supplied

Quantitative analysis of iron-containing protein myoglobin in different foodstuffs by liquid chromatography coupled to high-resolution inductively coupled plasma mass spectrometry.

Quantitative determination was made of the iron-containing protein myoglobin in a range of different foods, including meat, processed meat, fish, and shellfish, by liquid chromatography coupled to a double-focusing sector field inductively coupled plasma mass spectrometry (ICP-MS). The concentration of myoglobin determined in the samples ranged from 0 to 6.5 mg/kg, and the analytical precision (coefficient of variation) for the analysis of 8 replicate raw steak extracts was 2.1%. By using a double-focusing ICP-MS instrument, direct on-line detection of the most abundant iron isotope 56Fe was possible without interference from a major polyatomic interference (40Ar16O). Separation of myoglobin from other iron-containing compounds was facilitated by use of a gel filtration column (TSK Gel G2000SW) and Tris buffer (pH 7.2). The chromatographic column was coupled directly to the nebulizer of the ICP-MS instrument by a short piece of PEEK tubing. To ensure sufficient quality control throughout the study, a raw beefsteak sample was developed as an in-house reference material. The concentration of the heme-iron-containing protein myoglobin in this sample was determined by the developed method and independently by a conventional spectrophotometric method. The agreement between the 2 analytical techniques was very good. The detection limit (3 times the signal/noise ratio for a blank) of the reported method for myoglobin was 0.85 ng Fe/L.

Animals↗

PubMed2005

Opinion of newly wed Greek couples about the nature and functions of modern family. Similarities and differences with the opinion of Bulgarian couples.

BACKGROUND: Among the European countries, Greece has exhibited a significant decline in its total fertility rate. Unlike Bulgaria, Greece conducts little in-depth research to study comprehensively the attitudes of newlywed couples toward family planning and reproductive behaviour. AIM: The present study aimed at exploring the opinion of newly married Greek couples about the nature and functions of modern family and comparing them with those of Bulgarian couples. MATERIAL AND METHODS: We conducted two parallel cross-sectional studies gathering the primary data by individual questionnaire survey using established methods. RESULTS: More than half of the respondents planned to have a child within two years after marriage. Most of the respondents think that the main purpose of having children in a family is to give meaning to a person's life. In both Greece and Bulgaria giving birth to a child in a family is believed to be the consequence of merely life-experience related and emotional prerequisites that arise from the deeply rooted traditional attitudes in these countries towards the value and role of family. The prevailing opinion is that children should be raised by the parents in their parents' home until they become three years of age. Greek women are more inclined than Bulgarian women to stay at home and raise their children even until they complete school and are ready to care for them after graduation and marriage.

Adult↗

PubMed1991

Coupling of a mutated form of the human beta 2-adrenergic receptor to Gi and Gs. Requirement for multiple cytoplasmic domains in the coupling process.

We constructed five genes encoding mutant human beta 2-adrenergic receptor sequence (beta 2AR) which contained 12-22 amino acid substitutions with corresponding sequence from the human alpha 2AAR in order to assess the receptor domains involved in Gs versus Gi recognition and coupling. Mutant beta 2AR with substitutions in the N (S1)- and C-terminal (S2) portions of the third intracellular loop, the proximal cytoplasmic tail (S3), and two combinations thereof (S2,3 and S1,2,3), were stably expressed in Chinese hamster fibrobasts (CHW-1102), as were the human beta 2AR and alpha 2AAR at comparable receptor levels. All mutant receptors with S2 substitutions (i.e. S2, S2,3, S1,2,3) were significantly (approximately 85%) uncoupled from Gs. Upon exposure to pertussis toxin, which uncouples receptors from Gi, S1,2,3 exhibited a 526 +/- 99% increase in agonist-stimulated adenylylcyclase activity compared with a 59 +/- 13% increase with the wild type receptor. This enhanced ability of S1,2,3 to interact with Gs following pertussis toxin treatment indicates that, in the absence of toxin exposure, substantial coupling occurs between the mutant receptor and Gi. Mutant beta 2AR bearing only one or two alpha 2AAR-substituted sequences showed no such enhancement. Forskolin-stimulated enzyme activities were increased by pertussis toxin treatment to similar degrees in all clones examined, indicating that the observed effects are confined to the receptor-mediated pathway. In the absence of GTP, competition binding experiments with S1,2,3, beta 2AR and alpha 2AAR revealed that approximately 40-50% of the receptors formed a high affinity binding state for agonist. Pertussis toxin treatment markedly reduced this to approximately 19% with S1,2,3, while having no effect on beta 2AR and completely eliminating high affinity agonist binding to alpha 2AAR. These results suggest that S1,2,3 interacts with Gi as well as Gs, and that receptor:G protein coupling requires the concerted participation of multiple cytoplasmic receptor domains.

Adenosine Diphosphate Ribose↗

PubMed1979

Coupling of glucagon receptor to adenylyl cyclase. Requirement of a receptor-related guanyl nucleotide binding site for coupling of receptor to the enzyme.

Effects of glucagon and guanyl nucleotides on the rat liver plasma membrane adenylyl cyclase were studied. It was established that: 1) glucagon stimulates the fully guanyl-5'-yl imidodiphosphate (GMP-P(NH)P)-activated enzyme between 20 and 70%, provided a guanyl nucleotide is present in the assay; 2) glucagon has no effect on adenylyl cyclase activity in membranes activated fully by GMP-P(NH)P and then washed free of nucleotides. It is concluded that occupancy of the guanyl nucleotide binding site that activates the catalytic moiety of the system is not sufficient to promote hormone-receptor coupling to adenylyl cyclase and that occupancy of a second site by guanyl nucleotides is essential to effect stimulation of adenylyl cyclase by the glucagon-receptor complex. The data presented raise the question whether the guanyl nucleotide site that promotes coupling is distinct from the guanyl nucleotide site that modulates binding of glucagon to receptor and whether the occupancy of the guanyl nucleotide site associated with the catalytic moiety is necessary for coupling.

Adenylyl Cyclases↗

PubMed2004

GoLoco motif peptides as probes of Galpha subunit specificity in coupling of G-protein-coupled receptors to ion channels.

Biochemical and structural studies of signaling proteins have revealed critical features of peptide motifs at the interaction surfaces between proteins. Such information can be used to design small peptides that can be used as functional probes of specific interactions in signaling cascades. This article describes the use of a novel domain (the GoLoco motif) found in several members of the regulators of G-protein signaling (RGS) protein family to probe the specificity of Galpha subunit involvement in the coupling of dopamine and somatostatin receptors to ion channels in the AtT20 neuroendocrine cell line. Peptides encoding the GoLoco motifs of RGS12 and AGS3 were perfused into single cells during electrical recording of agonist-induced current responses by whole cell patch clamp methods. The particular sequences chosen have been demonstrated to bind selectively to the GDP-bound form of Galphai, but not Galphao, and preclude association of Gbetagamma and Galphai subunits. A functional manifestation of this property is observed in the progressive uncoupling of D2 dopamine receptors and Kir3.1/3.2 channels with repeated agonist application. Similar uncoupling is not observed with somatostatin receptors nor with D2 receptors coupling to calcium channels, suggesting Galpha subunit specificity in these signaling pathways. Motifs found in other proteins in the GPCR signaling machinery may also prove useful in assessing G-protein signaling specificity and complexity in single cells in the future.

Amino Acid Sequence↗

PubMed2005

G protein-coupled receptor kinase 2-mediated phosphorylation of ezrin is required for G protein-coupled receptor-dependent reorganization of the actin cytoskeleton.

G protein-coupled receptor kinase 2 (GRK2) phosphorylates and desensitizes activated G protein-coupled receptors (GPCRs). Here, we identify ezrin as a novel non-GPCR substrate of GRK2. GRK2 phosphorylates glutathione S-transferase (GST)-ezrin, but not an ezrin fusion protein lacking threonine 567 (T567), in vitro. These results suggest that T567, the regulatory phosphorylation site responsible for maintaining ezrin in its active conformation, represents the principle site of GRK2-mediated phosphorylation. Two lines of evidence indicate that GRK2-mediated ezrin-radixinmoesin (ERM) phosphorylation serves to link GPCR activation to cytoskeletal reorganization. First, in Hep2 cells muscarinic M1 receptor (M1MR) activation causes membrane ruffling. This ruffling response is ERM dependent and is accompanied by ERM phosphorylation. Inhibition of GRK2, but not rho kinase or protein kinase C, prevents ERM phosphorylation and membrane ruffling. Second, agonist-induced internalization of the beta2-adrenergic receptor (beta2AR) and M1MR is accompanied by ERM phosphorylation and localization of phosphorylated ERM to receptor-containing endocytic vesicles. The colocalization of internalized beta2AR and phosphorylated ERM is not dependent on Na+/H+ exchanger regulatory factor binding to the beta2AR. Inhibition of ezrin function impedes beta2AR internalization, further linking GPCR activation, GRK activity, and ezrin function. Overall, our results suggest that GRK2 serves not only to attenuate but also to transduce GPCR-mediated signals.

Actins↗

PubMed1991

Na(+)-coupled alternative to H(+)-coupled primary transport systems in bacteria.

Protons are the most common coupling ions in bacterial energy conversions. However, while many organisms, such as the alkaliphilic Bacilli, employ H(+)-bioenergetics for electron transport phosphorylation, they use Na+ as the coupling ion for transport and flagellar movement. The Na+ gradient required for these bioenergetic functions is established by the secondary Na+/H+ antiporter. In contrast, Vibrio alginolyticus and methanogenic bacteria have primary pumps for both H+ and Na+. They use the proton gradient for ATP synthesis while other, less energy-consuming membrane reactions are powered by the Na+ gradient. In a third mode, some anaerobic bacteria possess decarboxylases acting as primary Na+ pumps. For instance, in Klebsiella pneumoniae, the Na+ gradient established by oxaloacetate decarboxylase is used for the uptake of the growth substrate citrate, and Propionigenium modestum consumes the energy of the Na+ gradient formed by methylmalonyl-CoA decarboxylase directly for ATP synthesis.

Adenosine Triphosphate↗

PubMed2002

Post-translational proteolytic processing of the calcium-independent receptor of alpha-latrotoxin (CIRL), a natural chimera of the cell adhesion protein and the G protein-coupled receptor. Role of the G protein-coupled receptor proteolysis site (GPS) motif.

The calcium-independent receptor of alpha-latrotoxin (CIRL), a neuronal cell surface receptor implicated in the regulation of exocytosis, is a natural chimera of the cell adhesion protein and the G protein-coupled receptor (GPCR). In contrast with canonic GPCRs, CIRL consists of two heterologous non-covalently bound subunits, p120 and p85, due to endogenous proteolytic processing of the receptor precursor in the endoplasmic reticulum. Extracellularly oriented p120 contains hydrophilic cell adhesion domains, whereas p85 resembles a generic GPCR. We determined that the site of the CIRL cleavage is located within a juxtamembrane Cys- and Trp-rich domain of the N-terminal extracellular region of CIRL. Mutations in this domain make CIRL resistant to the cleavage and impair its trafficking. Therefore, we have named it GPS for G protein-coupled receptor proteolysis site. The GPS motif is found in homologous adhesion GPCRs and thus defines a novel receptor family. We postulate that the proteolytic processing and two-subunit structure is a common characteristic feature in the family of GPS-containing adhesion GPCRs.

Amino Acid Motifs↗