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PubMed1982

Role of membrane integrity and cation interaction for heart sarcolemmal adenylate cyclase and Na+-K+ ATPase.

The adenylate cyclase and Na+ -K+ ATPase activities decreased on storage at 4 degrees C as well as on freezing and thawing of the rat heart sarcolemma. Treatment of the sarcolemmal fraction with phospholipase C and trypsin also depressed the adenylate cyclase and Na+ -K+ ATPase activities; the Na+ -K+ ATPase was more sensitive to these treatments than the adenylate cyclase. When the sarcolemmal enzyme activities were determined in the presence of different concentrations of some cations the adenylate cyclase activity was enhanced and the Na+ -K+ ATPase activity was depressed by monovalent cations (Na+, K+, Rb+, Cs+, Li+, and NH+4). Divalent cations such as Sr2+, Ba2+, Co2+, and Mn2+ had biphasic or no effects on the adenylate cyclase activity but inhibited the Na+ -K+ ATPase activity. Although Ca2+, Ni2+, Cd2+, Cu2+, Hg2+, and Zn2+ depressed both Na+ -K+ ATPase and adenylate cyclase activities, the degree of inhibition of these enzymes was different. These results reveal the role of membrane integrity for full expression of the adenylate cyclase and Na+ -K+ ATPase activities, whereas both monovalent and divalent cations appear to regulate sarcolemma-bound enzyme activities.

Adenylyl Cyclases↗
PubMedDate not supplied

Cooperative and competitive spatial interactions in motion integration.

Recovering the velocity of objects moving in the visual field requires both the integration and segmentation of local neuronal responses elicited by moving stimuli in primary visual cortex. Herein, we investigate the effects of the contrast, density, spatial proximity, spatial frequency, and spatial configuration of component motions on these complementary processes. Measuring the ability of human observers to discriminate the global direction of motion displays composed of spatially distributed patches of drifting gratings whose motion is locally ambiguous, we provide psychophysical evidence that linking component motion across space is facilitated at low contrast and high patch density. Furthermore, direction discrimination depends on the spatial frequency of component gratings and is more accurate for spatial configurations that contain "virtual" L junctions as compared to configurations composed of "virtual" T junctions. We suggest that the conditions yielding global motion coherence can be accounted for by the existence of anisotropic cooperative/competitive, contrast-dependent, long-range interactions among oriented direction-selective units. In addition, we bring evidence that motion segmentation processes rely upon the processing of moving local spatial discontinuities. The results are discussed in the light of recent psychophysical and physiological evidence that long-range excitatory and inhibitory interactions within primary visual cortex modulate perceptual linking.

Contrast Sensitivity↗
PubMed1990

Alterations in the p'R promoter of coliphage lambda modify both its activity and interaction with the integration host factor (IHF).

A limited number of deletion/insertions and a point mutation in the -35 region of the p'R promoter of phage lambda were examined and found to influence both transcription and its repression by the integration host factor (IHF). Positive effects on transcription (in the absence of IHF) are small (up to 1.4-fold) and are caused by a deletion-substitution upstream of the -35/ihf site. Up to three base changes in the -35 promoter element seem to be tolerated, with only a small negative effect on transcription. In some cases, effective transcription requires supercoiling of such mutant template. Since an ihf sequence overlaps the -35 region of p'R, IHF represses transcription. Repression is correlated with IHF binding and consequent DNA bending, as assessed by gel retardation experiments. Nine p'R mutants were tested for their IHF binding and repression; the results confirm the consensus sequence, 5'-W2WWWWN7WWWWCARNWN2TTR derived from the hydroxyl radical footprinting, where the bold letters indicate the IHF-protected bases and W is A or T, R is A or G and N represents A, T, G or C. Perhaps surprisingly, some mutations just upstream or downstream of this ihf sequence also affect IHF binding, as observed not only for the pR'/ihf but also for the att H' site of lambda. Supercoiling in some cases permits the IHF-mediated repression to be overcome, probably by increasing the RNA polymerase binding and/or decreasing the interaction with IHF. All our data are consistent with a model which assumes that IHF initially binds to one or two ihf contact points depending on preexisting DNA topology, bends DNA, and completes the remaining contacts while finally adjusting the DNA conformation to establish the best fit within the minor groove of the double helix. Effective IHF repression of transcription would thus depend on several factors, including: (1) the sequence, and (2) the initial conformation of the ihf site, together with (3) the capacity of IHF to compete with RNA polymerase for the overlapping binding sites.

Bacterial Proteins↗
PubMed1998

Protein subunit interactions and structural integrity of amyloidogenic transthyretins: evidence from electrospray mass spectrometry.

Wild-type and variant transthyretins form amyloid fibrils in two different diseases. The biologically active form of transthyretin is a tetramer but there is evidence that a monomeric species is the amyloidogenic intermediate. Using mass spectrometry we have developed an approach to monitor the proportions of monomer and tetramer in wild-type and variant transthyretins, and found a strong correlation between the instability of the tetramer in the gas phase and the amyloidogenicity of the protein variant. The presence of water molecules in the central channel has been found to be critical for maintaining intact the complex in the gas phase, with additional stability observed in the presence of excess thyroxine. The solution structure of monomeric transthyretin under fibril-forming conditions was studied using hydrogen exchange monitored by mass spectrometry. The results show that Val30Met transthyretin, the commonest amyloidogenic variant, exhibits loss of hydrogen exchange protection substantially more rapidly than the wild-type protein, suggesting partial unfolding of the beta-sheet structure. These results provide new insights into the correlation between tetramer stability and amyloidogenicity as well as supporting a possible route to fibril formation via transient unfolding of the transthyretin monomer.

Amyloid↗
PubMed2003

Enhancing evolvability with mutation buffering mediated through multiple weak interactions.

The evolutionary adaptability of a system is dependent on three organizational properties, self-organizing dynamics that are hierarchically organized, component redundancy, and multiple weak interactions [Towards high evolvability dynamics, in: G. van de Vijver, S. Salthe, M. Delpos (Eds.), Evolutionary Systems, Kluwer Academic Publishers, Dordrecht, 1998, pp. 147-169]. This study reports on the use of the dual dynamics network model as an aid in understanding the role multiple weak interactions play in enhancing evolutionary adaptability. Dual dynamics networks are self-organizing systems that consist of simple components that change local state due to the coupled influences from connected components exerting strong discrete decision-making influences and from groups of components exerting multiple weak influences [J. Theor. Biol. 193 (1998) 287]. The dual dynamics model has been enhanced to support investigations of properties relevant to a system's capacity for evolvability, such as structure-function relationships, neutrality, adaptive tolerance, and evolutionary search performance. Three network types are investigated, each utilizing a different method of coupling strong and weak influences. The results demonstrate that the manner of coupling multiple weak interactions into the systems dynamics significantly affects the structure-function maps and the consequent evolvability characteristics. Specifically it is found that a form of coupling, denoted as linear modulation, enhances evolutionary adaptability. Linear modulation coupling requires that the weak interactions be integrated with strong interactions in a manner that implies a linear ordered relation between the possible state values of the components of the systems. When coupling functions that do not imply such an ordering of local state values are used, evolutionary adaptability is decreased.

Adaptation, Physiological↗
PubMed2003

Transgene integration, organization and interaction in plants.

It has been appreciated for many years that the structure of a transgene locus can have a major influence on the level and stability of transgene expression. Until recently, however, it has been common practice to discard plant lines with poor or unstable expression levels in favor of those with practical uses. In the last few years, an increasing number of experiments have been carried out with the primary aim of characterizing transgene loci and studying the fundamental links between locus structure and expression. Cereals have been at the forefront of this research because molecular, genetic and cytogenetic analysis can be carried out in parallel to examine transgene loci in detail. This review discusses what is known about the structure and organization of transgene loci in cereals, both at the molecular and cytogenetic levels. In the latter case, important links are beginning to be revealed between higher order locus organization, nuclear architecture, chromatin structure and transgene expression.

Models, Genetic↗
PubMed1990

Effects of contextual integration on recall of pictures by older adults.

This study investigated age-related differences in the ability to utilize integrative relationships between target and context as a memory support by directly manipulating the relationship between a target picture and context. We hypothesized that as the active integration required between target and cue increased, age differences would increase. Old and young adults were instructed to remember target pictures, each presented with a pictorial cue. The cue/target relationship was one of three types: categorically related (high integration condition), visually interacting (high integration condition), or unrelated and noninteracting (low integration condition). Cued recall of the targets was tested. The results indicated that the poorly integrated target-context relationship produced the largest age difference, supporting the integration hypothesis.

Adolescent↗
PubMed2001

Microbes and microbial toxins: paradigms for microbial-mucosal interactions II. The integrated response of the intestine to Clostridium difficile toxins.

Clostridium difficile, the major etiologic factor of antibiotic-associated diarrhea and colitis, mediates its effects by releasing two large protein exotoxins, toxins A and B. A major toxin effect is related to the disassembly of actin microfilaments, leading to impairment of tight junctions in human colonocytes. The mechanism of actin disaggregation involves monoglucosylation of the signaling proteins Rho A, Rac, and Cdc 42, which control stress fiber formation directly by toxins A and B. An important aspect of C. difficile infection is the acute necroinflammatory changes seen in patients with pseudomembranous colitis. The early mechanism of toxin-mediated inflammation involves toxin effects on cellular mitochondria, release of reactive oxygen species, and activation of mitogen-activated protein kinases and the transcription factor nuclear factor-kappaB. Injection of toxin A into animal intestine triggers secretion of fluid and intestinal inflammation characterized by epithelial cell destruction and neutrophil activation. A critical feature of C. difficile enterotoxicity is communication between enterocytes and lamina propria nerves, macrophages, and mast cells mediated via release of neuropeptides and proinflammatory cytokines.

Acute-Phase Proteins↗
PubMed1995

Evaluation of a distance consulting service based on interactive video and integrated computerized technology.

Telemedicine equipment was installed at a rural site in Drumheller and at Calgary, 85 miles (136 km) away. It allowed consultation between health-care providers at Drumheller and specialists and subspecialists at the Faculty of Medicine in Calgary. The efficacy of the system in providing more equitable access to health care for persons living in geographically remote sites was evaluated during a 12-month pilot project. Seventy-five encounters were attempted during the study. A total of 55 encounters (42 clinical and 13 non-clinical) were completed. The completed clinical encounters were distributed across a wide spectrum of medical specialties. Users of the system reported favourably on the impact of the telemedicine system on access to health services for rural patients, on diagnostic, investigative and management decisions, on patient and physician travel times, on feelings of professional isolation and educational opportunities and on overall patient health status. The study provides new knowledge and demonstrates the success of the technology in this project. As expected, other problems were raised and addressed in a preliminary manner including: the potential for health-provider education; acquisition and retention of rural physicians; ethical, legal and patient confidentiality issues; minimum acceptable technology; and network management issues.

Canada↗
PubMed1990

Two requirements for job contentment: autonomy and social integration.

The interaction of autonomy (control over work activities) and social integration (relationships with co-workers) was investigated in a sample of newly employed nurses in the 6th and 12th month of work. Those nurses with low autonomy and low social integration reported low job satisfaction and work motivation, poor commitment to the organization and less intent to stay on the job. They were older, with more experience and more education and tended to work on medical units. This study supports the notion of feminist psychologists that what women nurses want is "autonomy with connectedness".

Adult↗
PubMed2001

Antibody-antigen interactions measured by surface plasmon resonance: global fitting of numerical integration algorithms.

The interactions between adenylate kinase (AK) and a monoclonal antibody against AK (McAb3D3) were examined by means of optical biosensor technology, and the sensograms were fitted to four models using numerical integration algorithms. The interaction of a solution of McAb3D3 with immobilized AK follows a double exponential function and the data fitted well to an inhomogeneous ligand model. The interaction of a solution AK with immobilized McAb3D3 follows a single exponential function and the data fitted well to a pseudo-first order reaction model. The true association constants of AK binding to McAb3D3 in solution were obtained from competition BIAcore measurements. The difference in results obtained with solid-phase BIAcore and competition BIAcore may be due to rebinding of the dissociated analyte to the immobilized surface. The results obtained with BIAcore are compared to those obtained by ELISA methods. We suggest that the best method for analysis of BIAcore data is direct, global fitting of sensorgrams to numerical integration algorithms corresponding to the different possible models for binding.

Adenylate Kinase↗
PubMed1998

Ethanol and neurotransmitter interactions--from molecular to integrative effects.

There is extensive evidence that ethanol interacts with a variety of neurotransmitters. Considerable research indicates that the major actions of ethanol involve enhancement of the effects of gamma-aminobutyric acid (GABA) at GABAA receptors and blockade of the NMDA subtype of excitatory amino acid (EAA) receptor. Ethanol increases GABAA receptor-mediated inhibition, but this does not occur in all brain regions, all cell types in the same region, nor at all GABAA receptor sites on the same neuron, nor across species in the same brain region. The molecular basis for the selectivity of the action of ethanol on GaBAA receptors has been proposed to involve a combination of benzodiazepine subtype, beta 2 subunit, and a splice variant of the gamma 2 subunit, but substantial controversy on this issue currently remains. Chronic ethanol administration results in tolerance, dependence, and an ethanol withdrawal (ETX) syndrome, which are mediated, in part, by desensitization and/or down-regulation of GABAA receptors. This decrease in ethanol action may involve changes in subunit expression in selected brain areas, but these data are complex and somewhat contradictory at present. The sensitivity of NMDA receptors to ethanol block is proposed to involve the NMDAR2B subunit in certain brain regions, but this subunit does not appear to be the sole determinant of this interaction. Tolerance to ethanol results in enhanced EAA neurotransmission and NMDA receptor upregulation, which appears to involve selective increases in NMDAR2B subunit levels and other molecular changes in specific brain loci. During ETX a variety of symptoms are seen, including susceptibility to seizures. In rodents these seizures are readily triggered by sound (audiogenic seizures). The neuronal network required for these seizures is contained primarily in certain brain stem structures. Specific nuclei appear to play a hierarchical role in generating each stereotypical behavioral phases of the convulsion. Thus, the inferior colliculus acts to initiate these seizures, and a decrease in effectiveness of GABA-mediated inhibition in these neurons is a major initiation mechanism. The deep layers of superior colliculus are implicated in generation of the wild running behavior. The pontine reticular formation, substantia nigra and periaqueductal gray are implicated in generation of the tonic-clonic seizure behavior. The mechanisms involved in the recruitment of neurons within each network nucleus into the seizure circuit have been proposed to require activation of a critical mass of neurons. Achievement of critical mass may involve excess EAA-mediated synaptic neurotransmission due, in part, to upregulation as well as other phenomena, including volume (non-synaptic diffusion) neurotransmission. Effects of ETX on receptors observed in vitro may undergo amplification in vivo to allow the excess EAA action to be magnified sufficiently to produce synchronization of neuronal firing, allowing participation of the nucleus in seizure generation. GABA-mediated inhibition, which normally acts to limit excitation, is diminished in effectiveness during ETX, and further intensifies this excitation.

Animals↗