252 research outputs found
Die vorvertragliche Anzeigepflicht des Versicherungsnehmers im VVG 2008
No full textBarg ES. Die vorvertragliche Anzeigepflicht des Versicherungsnehmers im VVG 2008. Berlin: Logos-Verl.; 2008
Statistical Frailty Modeling for Quantitative Analysis of Exocytotic Events Recorded by Live Cell Imaging: Rapid Release of Insulin-Containing Granules Is Impaired in Human Diabetic β-cells
No full textHormones and neurotransmitters are released when secretory granules or synaptic vesicles fuse with the cell membrane, a process denoted exocytosis. Modern imaging techniques, in particular total internal reflection fluorescence (TIRF) microscopy, allow the investigator to monitor secretory granules at the plasma membrane before and when they undergo exocytosis. However, rigorous statistical approaches for temporal analysis of such exocytosis data are still lacking. We propose here that statistical methods from time-to-event (also known as survival) analysis are well suited for the problem. These methods are typically used in clinical settings when individuals are followed over time to the occurrence of an event such as death, remission or conception. We model the rate of exocytosis in response to pulses of stimuli in insulin-secreting pancreatic beta-cell from healthy and diabetic human donors using piecewise-constant hazard modeling. To study heterogeneity in the granule population we exploit frailty modeling, which describe unobserved differences in the propensity to exocytosis. In particular, we insert a discrete frailty in our statistical model to account for the higher rate of exocytosis in an immediately releasable pool (IRP) of insulin-containing granules. Estimates of parameters are obtained from maximum-likelihood methods. Since granules within the same cell are correlated, i.e., the data are clustered, a modified likelihood function is used for log-likelihood ratio tests in order to perform valid inference. Our approach allows us for example to estimate the size of the IRP in the cells, and we find that the IRP is deficient in diabetic cells. This novel application of time-to-event analysis and frailty modeling should be useful also for the study of other well-defined temporal events at the cellular level
Semidefinite programming bounds for few-distance sets in the Hamming and Johnson spaces
No full textWe study the maximum cardinality problem of a set of few distances in the
Hamming and Johnson spaces. We formulate semidefinite programs for this problem
and extend the 2011 works by Barg-Musin and Musin-Nozaki. As our main result,
we find new parameters for which the maximum size of two- and three-distance
sets is known exactly.Comment: Renew the whole article to add more results and author
Mechanisms of exocytosis in insulin-secreting B-cells and glucagon-secreting A-cells.
No full textIn pancreatic B- and A-cells, metabolic stimuli regulate biochemical and electrical processes that culminate in Ca2+-influx and release of insulin or glucagon, respectively. Like in other (neuro)endocrine cells, Ca2+-influx triggers the rapid exocytosis of hormone-containing secretory granules. Only a small fraction of granules (<1% in insulin-secreting B-cells) can be released immediately, while the remainder requires translocation to the plasma membrane and further "priming" for release by several ATP- and Ca2+-dependent reactions. Such functional organization may account for systemic features such as the biphasic time course of glucose-stimulated insulin secretion. Since this release pattern is altered in type-2 diabetes mellitus, it is conceivable that disturbances in the exocytotic machinery underlie the disease. Here I will review recent data from our laboratory relevant for the understanding of these processes in insulin-secreting B-cells and glucagon-secreting A-cells and for the identification of novel targets for antidiabetic drug action. Two aspects are discussed in detail: 1) The importance of a tight interaction between L-type Ca2+-channels and the exocytotic machinery for efficient secretion; and 2) the role of intragranular acidification for the priming of secretory granules and its regulation by a granular 65-kDa sulfonylurea-binding protein
Mechanisms of exocytosis in insulin-secreting B-cells and glucagon-secreting A-cells
No full textIn pancreatic B- and A-cells, metabolic stimuli regulate biochemical and electrical processes that culminate in Ca2+-influx and release of insulin or glucagon, respectively. Like in other (neuro)endocrine cells, Ca2+-influx triggers the rapid exocytosis of hormone-containing secretory granules. Only a small fraction of granules (<1% in insulin-secreting B-cells) can be released immediately, while the remainder requires translocation to the plasma membrane and further "priming" for release by several ATP- and Ca2+-dependent reactions. Such functional organization may account for systemic features such as the biphasic time course of glucose-stimulated insulin secretion. Since this release pattern is altered in type-2 diabetes mellitus, it is conceivable that disturbances in the exocytotic machinery underlie the disease. Here I will review recent data from our laboratory relevant for the understanding of these processes in insulin-secreting B-cells and glucagon-secreting A-cells and for the identification of novel targets for antidiabetic drug action. Two aspects are discussed in detail: 1) The importance of a tight interaction between L-type Ca2+-channels and the exocytotic machinery for efficient secretion; and 2) the role of intragranular acidification for the priming of secretory granules and its regulation by a granular 65-kDa sulfonylurea-binding protein.</p
Mechanisms of insulin exocytosis and release
No full textPopular Abstract in Swedish Insulin frisätts från B-cellerna i bukspottkörteln (pankreas) när blodsockerhalten ökar över den normala (80-100 mg per dl), exempelvis efter en kolhydrat- och sockerrik måltid. Medan ?friska? B-celler har förmågan att reagera kraftigt redan på små (10%) förändringar i blodsockerhalten, så utvecklar ?ålders-diabetiska? B-celler en blodsockerblindhet och insulinfrisättningen ökar inte tillräckligt för att balansera det ökade insulinbehovet. Inuti den insulinfrisättande B-cellen lagras insulin i ett stort antal små lagringsblåsor. Insulinblåsorna kan ses som en såpbubbla innehållande en kristall av insulin. För att insulin skall kunna utöva sin biologiska verkan måste dessa lagringsblåsor sammansmälta med den omgivande cellväggen (cellmembranet). Varje B-cell innehåller fler än 10 000 sådana insulinblåsor men endast en bråkdel (0,5%) av dessa är omedelbart frisättningsbara. En ökad kalciumkoncentration inuti B-cellen till följd av ett stimulerat kalciuminflöde är den signal som igångsätter frisättningen av insulin. Kalcium transporteras in i cellen genom ett speciliserat transportprotein som bildar en vattenfylld kanal genom cellväggen, s.k. kalciumkanaler. Avhandlingens första del undersöker förhållandet mellan dessa kalciumkanaler och insulinblåsorna. En viktig slutsats av detta arbete är att insulinblåsorna och kalciumkanalerna bildar en funktionell enhet. Detta gör att insulinblåsorna kan sammansmälta med cellmembranet mycket snabbt (inom en hundradels sekund) vid stimulering av insulinfrisättningen samtidigt som energiåtgången för att återställa kalciumhalten till vilonivån minimeras. En serie kemiska reaktioner är nödvändig för att göra insulinvesikeln frisättningskompetent. Avhandlingens andra huvudtema är undersökningar av dessa förlopp. Sådana undersökningar är viktiga eftersom störningar i dessa reaktioner kan tänkas medföra minskad insulinfrisättning, t.ex. den som uppträder vid åldersdiabetes. Vi har identifierat ett nytt och, som det förefaller, avgörande steg i utmognadsprocessen som medverkar i en surgörning (d.v.s. en sänkning av pH:t) av insulinblåsornas inre. Ett komplex av åtminstone tre äggviteämnen (proteiner) deltar i förloppet och skulle vara en ideal måltavla för nya blodsockersänkande diabetesmediciner. Intressant nog har vissa nu använda diabetesmediciner som ?biverkan? att de påverkar just utmognadsprocessen och surgörningen av blåsorna. En förhoppning är att vi genom att karakterisera dessa processer skall kunna ?skräddarsy? nya läkemedel som selektivit påverkar just dessa processer. I det avslutande arbetet har vi utvecklat tekniker som medger undersökningar av lagringsblåsorna inuti cellen innan insulin frisätts. De tekniker som hittills använts av oss och andra har endast medgivit undersökningar av det sista steget, d.v.s. uppträdandet av insulin utanför cellen eller blåsornas sammansmältning med cellmembranet. För att förstå hur insulin frisätts och vad som avgör lagringsblåsornas frisättningsförmåga är det naturligtvis viktigt att undersöka de tidigare stegen. Något tillspetsat kan man kanske säga att uppfattningen att man kan förstå insulinsekretionens reglering genom att enbart mäta insulin är lika naivt som att tro att man kan förstå hur en bil fungerar genom att undersöka vad som kommer ur avgasröret! Med hjälp av en teknik där vi gör insulinblåsorna fluorescerande (d.v.s. de utsänder ljus) har vi kunnat visa att enbart insulinblåsor som sitter fast vid cellmembranet frisätts i samband med stimulering. Vi visar också att antalet blåsor som sitter fast vid membranet väsentligt överstiger det antal som vid ett givet tillfälle kan frisättas varför regleringen av insulinfrisättningen till stor del kan ske genom att blåsornas frisättningsbarhet ökas eller minskas. Någon fysisk transport av vesiklar inuti cellen är alltså inte nödvändig, åtminstone inte i det korta perspektivet (<10 min). Vi har också kunnat visa att själva frisättningen av insulin är mycket (100-1000 gånger) långsammare än lagringsblåsornas sammansmältning med cellmembranet. Denna fördröjning beror på att det tar en viss tid (1-10 s) för att öppningen i membranet (fusionsporen) skall vidgas tillräckligt för att den i sammanhanget ganska stora insulinmolekylen (~0,000004 mm) skall kunna passera. Det framstår som troligt att en liknande fördröjning även sker i andra cellslag där äggviteämnen frisätts. Exempel på sådana celler är andra hormonproducerande celler men även frisättningen av s.k. neuropeptider i nervsystemet. Det är nu väsentligt att undersöka vad som normalt reglerar fusionsporen öppnande samt om denna process kan påverkas farmakologiskt.Endocrine cells as well as neurons release their hormones and transmitters by regulated exocytosis. In the pancreatic B-cell, stimuli like glucose initiate biochemical and electrical processes that culminate in influx of Ca2+, which then triggers exocytosis of insulin-containing granules. Fusion of the secretory vesicles occurs rapidly upon Ca2+-influx but requires a granule to be ?primed? by an ATP-, Ca2+- and temperature-dependent reaction. Only a small fraction of the B-cell's granules (~ 0.5 %) are in the primed state and can undergo exocytosis immediately upon Ca2+-influx. These granules are referred to as the readily releasable pool (RRP), whereas the remaining granules form a ?reserve? pool. The functional organization of the granules in a reserve pool and a readily releasable pool could account for the fact that glucose-stimulated insulin secretion follows a biphasic time course, with the early rapid component (1st phase secretion) corresponding to RRP release and the second slower component reflecting time- and ATP-dependent mobilization of granules from the reserve pool. The commonest form of human diabetes (type-2 diabetes) is associated with disturbances in this release pattern. In this thesis, electrophysiology, fluorescence microscopy and biochemistry were combined to explore mechanisms of granule trafficking, priming, exocytosis, and release in insulin-secreting B-cells. Three aspects are discussed in detail: 1) The importance of a tight interaction between L-type Ca2+-channels and the exocytotic machinery for efficient secretion; 2) A novel ATP-dependent priming reaction that is regulated by a granular 65-kDa sulfonylurea-binding protein, and involves granule acidification and ClC-3 chloride channels; and 3) A previously overlooked delay between fusion of the granule with the plasma membrane and insulin release. Since regulated secretion is very similar in all (neuro)-endocrine cells, the data obtained are likely to be relevant for peptide secretion in general
Mechanisms of insulin exocytosis and release
No full textEndocrine cells as well as neurons release their hormones and transmitters by regulated exocytosis. In the pancreatic B-cell, stimuli like glucose initiate biochemical and electrical processes that culminate in influx of Ca2+, which then triggers exocytosis of insulin-containing granules. Fusion of the secretory vesicles occurs rapidly upon Ca2+-influx but requires a granule to be ?primed? by an ATP-, Ca2+- and temperature-dependent reaction. Only a small fraction of the B-cell's granules (~ 0.5 %) are in the primed state and can undergo exocytosis immediately upon Ca2+-influx. These granules are referred to as the readily releasable pool (RRP), whereas the remaining granules form a ?reserve? pool. The functional organization of the granules in a reserve pool and a readily releasable pool could account for the fact that glucose-stimulated insulin secretion follows a biphasic time course, with the early rapid component (1st phase secretion) corresponding to RRP release and the second slower component reflecting time- and ATP-dependent mobilization of granules from the reserve pool. The commonest form of human diabetes (type-2 diabetes) is associated with disturbances in this release pattern. In this thesis, electrophysiology, fluorescence microscopy and biochemistry were combined to explore mechanisms of granule trafficking, priming, exocytosis, and release in insulin-secreting B-cells. Three aspects are discussed in detail: 1) The importance of a tight interaction between L-type Ca2+-channels and the exocytotic machinery for efficient secretion; 2) A novel ATP-dependent priming reaction that is regulated by a granular 65-kDa sulfonylurea-binding protein, and involves granule acidification and ClC-3 chloride channels; and 3) A previously overlooked delay between fusion of the granule with the plasma membrane and insulin release. Since regulated secretion is very similar in all (neuro)-endocrine cells, the data obtained are likely to be relevant for peptide secretion in general
2002 Albert Renold Career Development Award of the European Foundation for the Study of Diabetes
No full textIn-Situ Hollow Sample Setup Design for Mechanical Characterisation of Gaseous Hydrogen Embrittlement of Pipeline Steels and Welds
No full textThis work discusses the design and demonstration of an in-situ test setup for testing pipeline steels in a high pressure gaseous hydrogen (H2) environment. A miniature hollow pipe-like tensile specimen was designed that acts as the gas containment volume during the test. Specific areas of the specimen can be forced to fracture by selective notching, as performed on the weldment. The volume of H2 used was minimised so the test can be performed safely without the need of specialised equipment. The setup is shown to be capable of characterising Hydrogen Embrittlement (HE) in steels through testing an X60 pipeline steel and its weldment. The percentage elongation (%El) of the base metal was found to be reduced by 40% when tested in 100 barg H2. Reduction of cross-sectional area (%RA) was found to decrease by 28% and 11% in the base metal and weld metal, respectively, when tested in 100 barg H2. Benchmark test were performed at 100 barg N2 pressure. SEM fractography further indicated a shift from normal ductile fracture mechanisms to a brittle transgranular (TG) quasi-cleavage (QC) type fracture that is characteristic of HE
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