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1.
Exocytosis of insulin in vivo maturation of mouse endocrine pancreas
Aldo Rozzo, Tiziana Meneghel-Rozzo, Saška Lipovšek Delakorda, Shi-Bing Yang, Marjan Rupnik, 2009, published scientific conference contribution

Abstract: The aim of this study was to define when an insulin-positive cell becomes functional in vivo and starts to exocytose insulin in a regulated nutrient-dependent manner. Insulin-positive cells appear in embryonic life (midgestation) and complete their maturation, presumably around birth. In order to work with embryonic and newborn endocrine pancreas, we used organotypic slices. The mouse embryonic pancreas slices show high basal insulin release that is not further elevated by high glucose levels. Despite the presence of functional voltage-activated ion channels, the cells are not electrically active in the presence of secretagogues. At birth, the high basalinsulin release drops and, after postnatal day 2, the insulin-positive cells show both adult-like bursting electrical activity and hormone release induced by high glucose levels. These properties allowed us to define them as beta cells. Despite the apparent stability of the transcription factor profile reported in insulin-positive cells during late-embryonic life, functional beta cells appear only 2 days after birth.
Keywords: cell biology, insulin release, embrios, newborn, beta-cell maturation, developing pancreas
Published: 07.06.2012; Views: 528; Downloads: 5
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2.
Membrane potential and calcium dynamics in beta cells from mouse pancreas tissue slices
Marjan Rupnik, Andraž Stožer, Jurij Dolenšek, Borut Žalik, Maša Skelin, Marko Gosak, Denis Špelič, 2015, review article

Abstract: Beta cells in the pancreatic islets of Langerhans are precise biological sensors for glucose and play a central role in balancing the organism between catabolic and anabolic needs. A hallmark of the beta cell response to glucose are oscillatory changes of membrane potential that are tightly coupled with oscillatory changes in intracellular calcium concentration which, in turn, elicit oscillations of insulin secretion. Both membrane potential and calcium changes spread from one beta cell to the other in a wave-like manner. In order to assess the properties of the abovementioned responses to physiological and pathological stimuli, the main challenge remains how to effectively measure membrane potential and calcium changes at the same time with high spatial and temporal resolution, and also in as many cells as possible. To date, the most wide-spread approach has employed the electrophysiological patch-clamp method to monitor membrane potential changes. Inherently, this technique has many advantages, such as a direct contact with the cell and a high temporal resolution. However, it allows one to assess information from a single cell only. In some instances, this technique has been used in conjunction with CCD camera-based imaging, offering the opportunity to simultaneously monitor membrane potential and calcium changes, but not in the same cells and not with a reliable cellular or subcellular spatial resolution. Recently, a novel family of highly-sensitive membrane potential reporter dyes in combination with high temporal and spatial confocal calcium imaging allows for simultaneously detecting membrane potential and calcium changes in many cells at a time. Since the signals yielded from both types of reporter dyes are inherently noisy, we have developed complex methods of data denoising that permit for visualization and pixel-wise analysis of signals. Combining the experimental approach of high-resolution imaging with the advanced analysis of noisy data enables novel physiological insights and reassessment of current concepts in unprecedented detail.
Keywords: calcium sensors, membrane potential sensors, calcium imaging, membrane potential imaging, beta cell, pancreas, denoising, patch-clamp
Published: 22.06.2017; Views: 151; Downloads: 15
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