Iskanje po katalogu digitalne knjižnice

Opis: Paper artifacts susceptible to acid hydrolysis and mechanical stress require effective conservation methods to ensure their longevity. In this study, a novel approach for the deacidification of acidic paper using calcium carbonate (CaCO3) [1,2]-ethylcellulose nanoparticles (CaCO3-EC NPs) dispersed in a non-aqueous ethyl acetate solution is presented. The dispersions were carefully prepared and applied to model acidic paper samples using a dipcoating method and then analyzed for their effectiveness. Transmission electron microscopy showed the formation of agglomerates containing quadrangular alkaline nanoparticles with diameters of 40 to 100 nm and a total agglomerate size of 250 nm. Hydrodynamic analyzes indicate the presence of a swollen ethyl cellulose coating on these agglomerates, which facilitates their dispersion. The results show the effectiveness of the CaCO3-EC NPs system in neutralizing acidic components (change of paper pH from 4.3 to 7) due to the homogeneous distribution within the paper substrates, effectively arresting the degradation processes. Acid-base titration showed a linear correlation between the concentration of alkaline nanoparticles and the alkaline reserve, emphasizing the role of ethylcellulose in facilitating particle transport within the paper matrix. In addition, ethylcellulose was found to improve the mechanical properties of the treated paper, as demonstrated by the standard mechanical tests. Importantly, the optical properties remained unchanged after treatment, as no adverse changes in color were observed. These results underline the effectiveness of the developed deacidification dispersions for the treatment of acidic paper and potentially other cellulose-based cultural heritage documents prone to acidic degradation. This approach offers promising implications for preserving and restoring valuable historical materials.
Ključne besede: ethylcellulose, calcium carbonate, functional coating, deacidification, strengthening, cultural heritage
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 1
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Opis: Background: The crucial steps in beta cell stimulus-secretion coupling upon stimulation with glucose are oscillatory changes in metabolism, membrane potential, intracellular calcium concentration, and exocytosis. The changes in membrane potential consist of bursts of spikes, with silent phases between them being dominated by membrane repolarization and absence of spikes. Assessing intra- and intercellular coupling at the multicellular level is possible with ever-increasing detail, but our current ability to simultaneously resolve spikes from many beta cells remains limited to double-impalement electrophysiological recordings. Methods: Since multicellular calcium imaging of spikes would enable a better understanding of coupling between changes in membrane potential and calcium concentration in beta cell collectives, we set out to design an appropriate methodological approach. Results: Combining the acute tissue slice method with ultrafast calcium imaging, we were able to resolve and quantify individual spikes within bursts at a temporal resolution of >150 Hz over prolonged periods, as well as describe their glucose-dependent properties. In addition, by simultaneous patch-clamp recordings we were able to show that calcium spikes closely follow membrane potential changes. Both bursts and spikes coordinate across islets in the form of intercellular waves, with bursts typically displaying global and spikes more local patterns. Conclusions: This method and the associated findings provide additional insight into the complex signaling within beta cell networks. Once extended to tissue from diabetic animals and human donors, this approach could help us better understand the mechanistic basis of diabetes and find new molecular targets.
Ključne besede: beta cell, calcium imaging, calcium oscillations, calcium spikes, physiology
Objavljeno v DKUM: 24.01.2025; Ogledov: 0; Prenosov: 7
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Opis: Pancreatic beta cells are coupled excitable oscillators that synchronize their activity via different communication pathways. Their oscillatory activity manifests itself on multiple timescales and consists of bursting electrical activity, subsequent oscillations in the intracellular Ca 2 + , as well as oscillations in metabolism and exocytosis. The coordination of the intricate activity on the multicellular level plays a key role in the regulation of physiological pulsatile insulin secretion and is incompletely understood. In this paper, we investigate theoretically the principles that give rise to the synchronized activity of beta cell populations by building up a phenomenological multicellular model that incorporates the basic features of beta cell dynamics. Specifically, the model is composed of coupled slow and fast oscillatory units that reflect metabolic processes and electrical activity, respectively. Using a realistic description of the intercellular interactions, we study how the combination of electrical and metabolic coupling generates collective rhythmicity and shapes functional beta cell networks. It turns out that while electrical coupling solely can synchronize the responses, the addition of metabolic interactions further enhances coordination, the spatial range of interactions increases the number of connections in the functional beta cell networks, and ensures a better consistency with experimental findings. Moreover, our computational results provide additional insights into the relationship between beta cell heterogeneity, their activity profiles, and functional connectivity, supplementing thereby recent experimental results on endocrine networks.
Ključne besede: pancreatic, beta cells, oscilators, calcium signaling, cells signaling
Objavljeno v DKUM: 10.12.2024; Ogledov: 0; Prenosov: 5
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Opis: Many details of glucose-stimulated intracellular calcium changes in [beta] cells during activation, activity, and deactivation, as well as their concentration-dependence, remain to be analyzed. Classical physiological experiments indicated that in islets, functional differences between individual cells are largely attenuated, but recent findings suggest considerable intercellular heterogeneity, with some cells possibly coordinating the collective responses. To address the above with an emphasis on heterogeneity and describing the relations between classical physiological and functional network properties, we performed functional multicellular calcium imaging in mouse pancreas tissue slices over a wide range of glucose concentrations. During activation, delays to activation of cells and any-cell-to-first-responder delays are shortened, and the sizes of simultaneously responding clusters increased with increasing glucose concentrations. Exactly the opposite characterized deactivation. The frequency of fast calcium oscillations during activity increased with increasing glucose up to 12 mM glucose concentration, beyond which oscillation duration became longer, resulting in a homogenous increase in active time. In terms of functional connectivity, islets progressed from a very segregated network to a single large functional unit with increasing glucose concentration. A comparison between classical physiological and network parameters revealed that the first-responders during activation had longer active times during plateau and the most active cells during the plateau tended to deactivate later. Cells with the most functional connections tended to activate sooner, have longer active times, and deactivate later. Our findings provide a common ground for recent differing views on [beta] cell heterogeneity and an important baseline for future studies of stimulus-secretion and intercellular coupling. NEW & NOTEWORTHY: We assessed concentration-dependence in coupled [beta] cells, degree of functional heterogeneity, and uncovered possible specialized subpopulations during the different phases of the response to glucose at the level of many individual cells. To this aim, we combined acute mouse pancreas tissue slices with functional multicellular calcium imaging over a wide range from threshold (7 mM) and physiological (8 and 9 mM) to supraphysiological (12 and 16 mM) glucose concentrations, classical physiological, and advanced network analyses.
Ključne besede: beta cells, calcium imaging, glucose-dependence, network analysis
Objavljeno v DKUM: 15.10.2024; Ogledov: 0; Prenosov: 19
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Opis: Although mice are a very instrumental model in islet beta cell research, possible phenotypic differences between strains and substrains are largely neglected in the scientific community. In this study, we show important phenotypic differences in beta cell responses to glucose between C57BL/6J, C57BL/6N, and NMRI mice, i.e., the three most commonly used strains. High-resolution multicellular confocal imaging of beta cells in acute pancreas tissue slices was used to measure and quantitatively compare the calcium dynamics in response to a wide range of glucose concentrations. Strain- and substrain-specific features were found in all three phases of beta cell responses to glucose: a shift in the dose-response curve characterizing the delay to activation and deactivation in response to stimulus onset and termination, respectively, and distinct concentration-encoding principles during the plateau phase in terms of frequency, duration, and active time changes with increasing glucose concentrations. Our results underline the significance of carefully choosing and reporting the strain to enable comparison and increase reproducibility, emphasize the importance of analyzing a number of different beta cell physiological parameters characterizing the response to glucose, and provide a valuable standard for future studies on beta cell calcium dynamics in health and disease in tissue slices.
Ključne besede: beta cell, mouse models, calcium imaging, glucose-dependence, tissue slice
Objavljeno v DKUM: 15.07.2024; Ogledov: 148; Prenosov: 22
Celotno besedilo (4,45 MB)
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