Interaction Between Equally Charged Membrane Surfaces Mediated by Positively and Negatively Charged Macro-Ions

In biological systems, charged membrane surfaces are surrounded by charged molecules such as electrolyte ions and proteins. Our recent experiments in the systems of giant phospholipid vesicles indicated that some of the blood plasma proteins (macro-ions) may promote adhesion between equally charged membrane surfaces. In this work, theory was put forward to describe an IgG antibody-mediated attractive interaction between negatively charged membrane surfaces which was observed in experiments on giant phospholipid vesicles with cardiolipin-containing membranes. The attractive interactions between negatively charged membrane surfaces in the presence of negatively and positively charged spherical macro-ions are explained using functional density theory and Monte Carlo simulations. Both, the rigorous solution of the variational problem within the functional density theory and the Monte Carlo simulations show that spatial and orientational ordering of macro-ions may give rise to an attractive interaction between negatively charged membrane surfaces. It is also shown that the distinctive spatial distribution of the charge within the macro-ions (proteins) is essential in this process.     

Biological impact of polyacetal particles on loosening of isoelastic stems

The aim of our study was to identify biological factors responsible for premature loosening of polyacetal hip stems. The results of histological analyses of the tissue around 11 total hip prostheses with loosened polyacetal femoral stems were compared to those obtained in a group of 11 total hip prostheses with loosened metal (CoCr) femoral components. A higher number of polymer wear particles surrounded by giant cells, more bone chips, and a more extensive necrosis were found around loosened polyacetal stems. Histomorphological characteristics of polyacetal wear particles containing BaSO(4) granules in the tissue around loosened polyacetal stems were described. Radiological evaluation of the wear of polyethylene cups suggested that elastic modulus of the stem had no influence on the wear of polyethylene cups. This study indicates that polyacetal wear particles have a great biological potential accelerating the process of loosening.     

Rab3a Is Critical for Trapping Alpha-MSH Granules in the High Ca2+-Affinity Pool by Preventing Constitutive Exocytosis

Rab3a is a small GTPase of the Rab3 subfamily that acts during late stages of Ca²⁺-regulated exocytosis. Previous functional analysis in pituitary melanotrophs described Rab3a as a positive regulator of Ca²⁺-dependent exocytosis. However, the precise role of the Rab3a isoform on the kinetics and intracellular [Ca²⁺] sensitivity of regulated exocytosis, which may affect the availability of two major peptide hormones, α-melanocyte stimulating hormone (α-MSH) and β-endorphin in plasma, remain elusive. We employed Rab3a knock-out mice (Rab3a KO) to explore the secretory phenotype in melanotrophs from fresh pituitary tissue slices. High resolution capacitance measurements showed that Rab3a KO melanotrophs possessed impaired Ca²⁺-triggered secretory activity as compared to wild-type cells. The hampered secretion was associated with the absence of cAMP-guanine exchange factor II/ Epac2-dependent secretory component. This component has been attributed to high Ca²⁺-sensitive release-ready vesicles as determined by slow photo-release of caged Ca²⁺. Radioimmunoassay revealed that α-MSH, but not β-endorphin, was elevated in the plasma of Rab3a KO mice, indicating increased constitutive exocytosis of α-MSH. Increased constitutive secretion of α-MSH from incubated tissue slices was associated with reduced α-MSH cellular content in Rab3a-deficient pituitary cells. Viral re-expression of the Rab3a protein in vitro rescued the secretory phenotype of melanotrophs from Rab3a KO mice. In conclusion, we suggest that Rab3a deficiency promotes constitutive secretion and underlies selective impairment of Ca²⁺-dependent release of α-MSH.     

Plasticity in Dendroclimatic Response across the Distribution Range of Aleppo Pine (Pinus halepensis)

We investigated the variability of the climate-growth relationship of Aleppo pine across its distribution range in the Mediterranean Basin. We constructed a network of tree-ring index chronologies from 63 sites across the region. Correlation function analysis identified the relationships of tree-ring index to climate factors for each site. We also estimated the dominant climatic gradients of the region using principal component analysis of monthly, seasonal, and annual mean temperature and total precipitation from 1,068 climatic gridpoints. Variation in ring width index was primarily related to precipitation and secondarily to temperature. However, we found that the dendroclimatic relationship depended on the position of the site along the climatic gradient. In the southern part of the distribution range, where temperature was generally higher and precipitation lower than the regional average, reduced growth was also associated with warm and dry conditions. In the northern part, where the average temperature was lower and the precipitation more abundant than the regional average, reduced growth was associated with cool conditions. Thus, our study highlights the substantial plasticity of Aleppo pine in response to different climatic conditions. These results do not resolve the source of response variability as being due to either genetic variation in provenance, to phenotypic plasticity, or a combination of factors. However, as current growth responses to inter-annual climate variability vary spatially across existing climate gradients, future climate-growth relationships will also likely be determined by differential adaptation and/or acclimation responses to spatial climatic variation. The contribution of local adaptation and/or phenotypic plasticity across populations to the persistence of species under global warming could be decisive for prediction of climate change impacts across populations. In this sense, a more complex forest dynamics modeling approach that includes the contribution of genetic variation and phenotypic plasticity can improve the reliability of the ecological inferences derived from the climate-growth relationships.     

The Relationship between Membrane Potential and Calcium Dynamics in Glucose-Stimulated Beta Cell Syncytium in Acute Mouse Pancreas Tissue Slices

Oscillatory electrical activity is regarded as a hallmark of the pancreatic beta cell glucose-dependent excitability pattern. Electrophysiologically recorded membrane potential oscillations in beta cells are associated with in-phase oscillatory cytosolic calcium activity ([Ca²⁺]_i) measured with fluorescent probes. Recent high spatial and temporal resolution confocal imaging revealed that glucose stimulation of beta cells in intact islets within acute tissue slices produces a [Ca²⁺]_i change with initial transient phase followed by a plateau phase with highly synchronized [Ca²⁺]_i oscillations. Here, we aimed to correlate the plateau [Ca²⁺]_i oscillations with the oscillations of membrane potential using patch-clamp and for the first time high resolution voltage-sensitive dye based confocal imaging. Our results demonstrated that the glucose-evoked membrane potential oscillations spread over the islet in a wave-like manner, their durations and wave velocities being comparable to the ones for [Ca²⁺]_i oscillations and waves. High temporal resolution simultaneous records of membrane potential and [Ca²⁺]_i confirmed tight but nevertheless limited coupling of the two processes, with membrane depolarization preceding the [Ca²⁺]_i increase. The potassium channel blocker tetraethylammonium increased the velocity at which oscillations advanced over the islet by several-fold while, at the same time, emphasized differences in kinetics of the membrane potential and the [Ca²⁺]_i. The combination of both imaging techniques provides a powerful tool that will help us attain deeper knowledge of the beta cell network.     

The efficiency of a closed-loop chemical-free water treatment system for cyprinid fish farms

The study presented has been carried out to evaluate the treatment performance, fish production and water consumption of a closed-loop chemical-free water treatment system for small-scale cyprinid fish farms. The closed-loop system consisted of a 36 m³ experimental pond (Pond A) with initial carp load of 1 kg/m³ (34 Cyprinus c. carpio); of a treatment train (TT) with a roughing filter (RF), glass fibre filters (GFF), and UV-C units (UV); and of an ultrasound unit (US) installed in the corner of the pond. The average circulation of the water in the closed-loop system was 2.3 times per day. Pond A was compared with a control pond (Pond B) of the same dimensions and fish load but with no TT or US. The TT was efficient in the removal of total suspended solids, biochemical oxygen demand, chemical oxygen demand, total coliforms (TC), and faecal coliforms (FC), reaching 35%, 42%, 33%, 37%, 91% and 91% removal, respectively. The majority of pollutant removal took place in the RF, while the GFF contributed mostly to the removal of TC and FC. UV did not contribute to the removal of bacteria, mostly due to low TC and FC inputs. The removal of nutrients in the TT (ammonia, nitrites, nitrates, total phosphorous and orto-phosphate) was not efficient. Despite this, Pond A had markedly lower nutrient concentrations compared to Pond B, and all the mean values of the measured parameters except nitrites and total phosphorous in Pond A were below legislation limit. Specific growth rate and fish body weight increase in Pond A were higher than in Pond B (0.3%/day, 0.2%/day, 152% and 115%, respectively) indicating better rearing conditions in Pond A. However, fish showed with 2.8 in Pond A and 3.3 in Pond B poor feed conversion rate over warm months. Higher water consumption in Pond A was due to various interventions during the pilot operation that can be reduced in normal operation. The results showed that the closed-loop system presented could be useful for semi-natural fish farming of 1-2 kg fish/m³. However, the system should be improved with regular sedimented algae removal to avoid nutrient accumulation.     

Horseshoe bats make adaptive prey-selection decisions, informed by echo cues

Foragers base their prey-selection decisions on the information acquired by the sensory systems. In bats that use echolocation to find prey in darkness, it is not clear whether the specialized diet, as sometimes found by faecal analysis, is a result of active decision-making or rather of biased sensory information. Here, we tested whether greater horseshoe bats decide economically when to attack a particular prey item and when not. This species is known to recognize different insects based on their wing-beat pattern imprinted in the echoes. We built a simulation of the natural foraging process in the laboratory, where the bats scanned for prey from a perch and, upon reaching the decision to attack, intercepted the prey in flight. To fully control echo information available to the bats and assure its unambiguity, we implemented computer-controlled propellers that produced echoes resembling those from natural insects of differing profitability. The bats monitored prey arrivals to sample the supply of prey categories in the environment and to inform foraging decisions. The bats adjusted selectivity for the more profitable prey to its inter-arrival intervals as predicted by foraging theory (an economic strategy known to benefit fitness). Moreover, unlike in previously studied vertebrates, foraging performance of horseshoe bats was not limited by costly rejections of the profitable prey. This calls for further research into the evolutionary selection pressures that sharpened the species's decision-making capacity.     

On the role of anisotropy of membrane constituents in formation of a membrane neck during budding of a multicomponent membrane

The expression for the isotropic membrane bending energy was generalized for the case of a multicomponent membrane where the membrane constituents (single molecules or small complexes of molecules-membrane inclusions) were assumed to be anisotropic. Using this generalized expression for the membrane energy it was shown that the change of intrinsic shape of membrane components may induce first-order-like shape transitions leading to the formation of a membrane neck. The predicted discontinuous membrane shape transition and the concomitant lateral segregation of membrane components were applied to study membrane budding. Based on the results presented we conclude that the budding process might be driven by accumulation of anisotropic membrane components in the necks connecting the bud and the parent membrane, and by accumulation of isotropic (conical) membrane components on the bud. Both processes may strongly depend on the intrinsic shape of membrane components and on the direct interactions between them.     

Regulation of IGF-I function by proinflammatory cytokines: at the interface of immunology and endocrinology

During the past decade, the immune and endocrine systems have been discovered to interact in controlling physiologic processes as diverse as cell growth and differentiation, metabolism, and even human and animal behavior. The interaction between these two major physiological systems is a bi-directional process. While it has been well documented that hormones, including prolactin (PRL), growth hormone (GH), insulin-like growth factor-I (IGF-I), and thyroid-stimulating hormone (TSH), regulate a variety of immune events, a great deal of data have accumulated supporting the notion that cytokines from the innate immune system also affect the neuroendocrine system. Communication between these two systems coordinates processes that are necessary to maintain homeostasis. Proinflammatory cytokines often act as negative regulatory signals that temper the action of hormones and growth factors. This system of 'checks and balances' is an active, ongoing process, even in healthy individuals. Dysregulation of this process has been implicated as a potential pathogenic factor in the development of co-morbid conditions associated with several chronic inflammatory diseases, including type 2 diabetes, cardiovascular disease, cerebrovascular disease, inflammatory bowel disease, rheumatoid arthritis, major depression, and even normal aging. Over the past decade, research in our laboratory has focused on the ability of the major proinflammatory cytokines, tumor necrosis factor (TNF)alpha and interleukin (IL)-1beta, to induce a state of IGF resistance. This review will highlight these and other new findings by explaining how proinflammatory cytokines induce resistance to the major growth factor, insulin-like growth factor-I (IGF-I). We also highlight that IGF-I can induce resistance or reduce sensitivity to brain TNFalpha and discuss how TNFalpha, IL-1beta, and IGF-I interact to regulate several aspects of behavior and cognition.     

A combined NMR and molecular dynamics simulation study to determine the conformational properties of agonists and antagonists against experimental autoimmune encephalomyelitis

Myelin basic protein (MBP) is one of the best characterized autoantigens causing multiple sclerosis (MS), via a procedure that involves a stable formation of the trimolecular complex of a T-cell Receptor (TCR), an MBP epitope, and the receptor HLA-DR2b. Experimental autoimmune encephalomyelitis (EAE) is considered as an instructive model for MS in humans, and plenty of X-ray data is available for a number of EAE inducing peptide-receptor complexes. To date, though, there are no data available for complexes involving peptides reversing EAE, namely antagonists. Conformational properties of the EAE inducing epitope MBP(87-99) were analyzed in DMSO using the NOE connectivities and vicinal H(N)-H(alpha) coupling constants, and compared with the antagonist altered peptide ligands. A robust method, which is based on a combination of molecular dynamics and energy minimization, is proposed for identifying the putative bioactive conformations. Generated conformations are compared with the known X-ray structure of MBP(83-96) (human sequence numbering) in the HLA-DR2b complex. The structural motif for the agonist-antagonist activity is discussed.