1. Critical transitions in pancreatic isletsDean Korošak, Sandra Postić, Andraž Stožer, Boštjan Podobnik, Marjan Rupnik, 2025, original scientific article Abstract: Calcium signals in pancreatic � cell collectives show a sharp transition from uncorrelated to correlated state resembling a phase transition as the slowly increasing glucose concentration crosses the tipping point. However, the exact nature or the order of this phase transition is not well understood. Using confocal microscopy to record the collective calcium activation of � cells in an intact islet under changing glucose concentration in an increasing and then decreasing way, we first show that in, addition to the sharp transition, the coordinated calcium response exhibits a hysteresis indicating a critical, first-order transition. A network model of � cells combining link selection and coordination mechanisms capture the observed hysteresis loop and the critical nature of the transition. Our results point towards an understanding of the role of islets as tipping elements in the pancreas that, interconnected by perfusion, diffusion, and innervation, cause the tipping dynamics and abrupt insulin release.
Keywords: cellular organization, physiology & dynamics, phase transitions in biological systems, complex networks, endocrine system, optical microscopy
Published in DKUM: 19.03.2025; Views: 0; Downloads: 2
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2. The microdynamics shaping the relationship between democracy and corruptionBoris Podobnik, Marko Jusup, Dean Korošak, Petter Holme, Tomislav Lipić, 2022, original scientific article Abstract: Physics has a long tradition of laying rigorous quantitative foundations for social phenomena. Here, we up the ante for physics' forays into the territory of social sciences by (i) empirically documenting a tipping point in the relationship between democratic norms and corruption suppression, and then (ii) demonstrating how such a tipping point emerges from a micro-scale mechanistic model of spin dynamics in a complex network. Specifically, the tipping point in the relationship between democratic norms and corruption suppression is such that democratization has little effect on suppressing corruption below a critical threshold, but a large effect above the threshold. The micro-scale model of spin dynamics underpins this phenomenon by reinterpreting spins in terms of unbiased (i.e. altruistic) and biased (i.e. parochial) other-regarding behaviour, as well as the corresponding voting preferences. Under weak democratic norms, dense social connections of parochialists enable coercing enough opportunist voters to vote in favour of perpetuating parochial in-group bias. Society may, however, strengthen democratic norms in a rapid turn of events during which opportunists adopt altruism and vote to subdue bias. The emerging model outcome at the societal scale thus mirrors the data, implying that democracy either perpetuates or suppresses corruption depending on the prevailing democratic norms.
Keywords: tipping point, complex network, sociophysics
Published in DKUM: 13.03.2025; Views: 0; Downloads: 2
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3. Physiological levels of adrenaline fail to stop pancreatic beta cell activity at unphysiologically high glucose levelsNastja Sluga, Lidija Križančić Bombek, Jasmina Kerčmar, Srdjan Sarikas, Sandra Postić, Johannes Pfabe, Maša Skelin, Dean Korošak, Andraž Stožer, Marjan Rupnik, 2022, original scientific article Abstract: Adrenaline inhibits insulin secretion from pancreatic beta cells to allow an organism to cover immediate energy needs by unlocking internal nutrient reserves. The stimulation of α2-adrenergic receptors on the plasma membrane of beta cells reduces their excitability and insulin secretion mostly through diminished cAMP production and downstream desensitization of late step(s) of exocytotic machinery to cytosolic Ca2+ concentration ([Ca2+]c). In most studies unphysiologically high adrenaline concentrations have been used to evaluate the role of adrenergic stimulation in pancreatic endocrine cells. Here we report the effect of physiological adrenaline levels on [Ca2+]c dynamics in beta cell collectives in mice pancreatic tissue slice preparation. We used confocal microscopy with a high spatial and temporal resolution to evaluate glucose-stimulated [Ca2+]c events and their sensitivity to adrenaline. We investigated glucose concentrations from 8-20 mM to assess the concentration of adrenaline that completely abolishes [Ca2+]c events. We show that 8 mM glucose stimulation of beta cell collectives is readily inhibited by the concentration of adrenaline available under physiological conditions, and that sequent stimulation with 12 mM glucose or forskolin in high nM range overrides this inhibition. Accordingly, 12 mM glucose stimulation required at least an order of magnitude higher adrenaline concentration above the physiological level to inhibit the activity. To conclude, higher glucose concentrations stimulate beta cell activity in a non-linear manner and beyond levels that could be inhibited with physiologically available plasma adrenaline concentration.
Keywords: adrenaline, islets, beta cells, cAMP, concentration dependency, [Ca2+]c oscillations, forskolin
Published in DKUM: 04.07.2024; Views: 155; Downloads: 18
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4. pH-dependence of glucose- dependent activity of beta cell networks in acute mouse pancreatic tissue sliceSandra Postić, Marko Gosak, Wen-Hao Tsai, Johannes Pfabe, Srdjan Sarikas, Andraž Stožer, Dean Korošak, Shi-Bing Yang, Marjan Rupnik, 2022, original scientific article Abstract: Extracellular pH has the potential to affect various aspects of the pancreatic beta cell function. To explain this effect, a number of mechanisms was proposed involving both extracellular and intracellular targets and pathways. Here, we focus on reassessing the influence of extracellular pH on glucose-dependent beta cell activation and collective activity in physiological conditions. To this end we employed mouse pancreatic tissue slices to perform high-temporally resolved functional imaging of cytosolic Ca2+ oscillations. We investigated the effect of either physiological H+ excess or depletion on the activation properties as well as on the collective activity of beta cell in an islet. Our results indicate that lowered pH invokes activation of a subset of beta cells in substimulatory glucose concentrations, enhances the average activity of beta cells, and alters the beta cell network properties in an islet. The enhanced average activity of beta cells was determined indirectly utilizing cytosolic Ca2+ imaging, while direct measuring of insulin secretion confirmed that this enhanced activity is accompanied by a higher insulin release. Furthermore, reduced functional connectivity and higher functional segregation at lower pH, both signs of a reduced intercellular communication, do not necessary result in an impaired insulin release.
Keywords: insulin secretion, membrane excitability, potassium channels, beta cell network, collective activity, calcium waves, pancreatic islets, pH-dependence
Published in DKUM: 01.07.2024; Views: 149; Downloads: 6
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5. Dinamika enodimenzionalnih sistemovVladimir Grubelnik, Marko Marhl, 2024, reviewed university, higher education or higher vocational education textbook Abstract: Učbenik obravnava enodimenzionalne dinamične sisteme z elementarnim pristopom. Cilj je študentom omogočiti boljše razumevanje temeljnih načel dinamike sistemov, kot so določitev stacionarnih stanj, stabilnostna analiza, bifurkacije in dolgoročno obnašanje sistemov. Učbenik je zasnovan predvsem za študente fizike, vendar je uporaben tudi za druge smeri, kjer je matematično modeliranje dinamičnih sistemov del učnega načrta. Vsebinski sklopi učbenika zajemajo osnovne značilnosti dinamičnih sistemov, geometrijski pristop reševanja enodimenzionalnih sistemov, tokove na krožnici, bifurkacije in njihove značilnosti, enodimenzionalne preslikave (mape) ter številne primere enodimenzionalnih sistemov v fiziki, biologiji in kemiji. Primeri so izbrani tako, da študentom pomagajo razvijati intuicijo za dinamiko bolj kompleksnih več dimenzionalnih sistemov, s katerimi se soočajo v vsakdanjem življenju.
Keywords: dinamika sistemov, povratne zanke, stabilnostna analiza, bifurkacije, logistična mapa, kaos
Published in DKUM: 13.02.2024; Views: 368; Downloads: 65
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7. Collective sensing of ß-cells generates the metabolic codeDean Korošak, Marjan Rupnik, 2018, original scientific article Keywords: collective sensing, pancreatic islets, spin glass models, metabolic code, Ca2+ imaging, Ca2+ signaling, correlations, intercellular communication
Published in DKUM: 25.01.2018; Views: 1646; Downloads: 130
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8. Quantifying soil complexity using network models of soil porous structureMarko Samec, A. Santiago, J. P. Cardenas, R. M. Benito, A. M. Tarquis, Sacha Jon Mooney, Dean Korošak, 2013, original scientific article Abstract: This paper describes an investigation into the properties of spatially embedded complex networks representing the porous architecture of soil systems. We suggest an approach to quantify the complexity of soil pore structure based on the node-node link correlation properties of the networks. We show that the complexity depends on the strength of spatial embedding of the network and that this is related to the transition from a non-compact to compact phase of the network.
Keywords: soil complexity, soil pore networks, complex systems
Published in DKUM: 21.07.2017; Views: 1476; Downloads: 339
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9. Functional connectivity in islets of Langerhans from mouse pancreas tissue slicesAndraž Stožer, Marko Gosak, Jurij Dolenšek, Matjaž Perc, Marko Marhl, Marjan Rupnik, Dean Korošak, 2013, original scientific article Abstract: We propose a network representation of electrically coupled beta cells in islets of Langerhans. Beta cells are functionally connected on the basis of correlations between calcium dynamics of individual cells, obtained by means of confocal laser-scanning calcium imaging in islets from acute mouse pancreastissue slices. Obtained functional networks are analyzed in the light of known structural and physiological properties of islets. Focusing on the temporal evolution of the network under stimulation with glucose, we show thatthe dynamics are more correlated under stimulation than under non-stimulated conditions and that the highest overall correlation, largely independent of Euclidean distances between cells, is observed in the activation and deactivation phases when cells are driven by the external stimulus. Moreover, we find that the range of interactions in networks during activity shows a clear dependence on the Euclidean distance, lending support to previous observations that beta cells are synchronized via calcium waves spreading throughout islets. Most interestingly, the functional connectivity patterns between beta cells exhibit small-world properties, suggesting that beta cells do not form a homogeneous geometric network but are connected in a functionally more efficient way. Presented results provide support for the existing knowledge of beta cell physiology from a network perspective and shedimportant new light on the functional organization of beta cell syncitia whose structural topology is probably not as trivial as believed so far.
Keywords: islets of Langerhans, mouse pancreas
Published in DKUM: 16.06.2017; Views: 1540; Downloads: 422
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10. Schottkyjeva bariera : moderni pogledi na star problemDean Korošak, Bruno Cvikl, 1998, review article Abstract: The description of the metal semiconductor contact in the framework of the general model incorporating the interfacial control layer between the metal and the ordered semiconductor is given. Special attention is given to the iCB Schottky structures for nonzero acceleration voltage featuring the disordered interfacial control layer characterized by the metal atoms incorporated into the semiconductor lattice and the DIGS continuum. The expression for the Schottky barrier height variation in ICB structures is given.
Keywords: površine, kovine, polprevodniki, tanke plasti
Published in DKUM: 10.07.2015; Views: 1318; Downloads: 51
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