Search results for "CALCIUM"
showing 10 items of 1740 documents
Morphogenetically active scaffold for osteochondral repair (Polyphosphate/alginate/N,O-carboxymethyl chitosan)
2016
Here we describe a novel bioinspired hydrogel material that can be hardened with calcium ions to yield a scaffold material with viscoelastic properties matching those of cartilage. This material consists of a negatively charged biopolymer triplet, composed of morphogenetically active natural inorganic polyphosphate (polyP), along with the likewise biocompatible natural polymers N,O-carboxymethyl chitosan (N,O-CMC) and alginate. The porosity of the hardened scaffold material obtained after calcium exposure can be adjusted by varying the pre-processing conditions. Various compression tests were applied to determine the local (nanoindentation) and bulk mechanical properties (tensile/compressio…
Enzymatically Synthesized Inorganic Polymers as Morphogenetically Active Bone Scaffolds
2014
In recent years a paradigm shift in understanding of human bone formation has occurred that starts to change current concepts in tissue engineering of bone and cartilage. New discoveries revealed that fundamental steps in biomineralization are enzyme driven, not only during hydroxyapatite deposition, but also during initial bioseed formation, involving the transient deposition and subsequent transformation of calcium carbonate to calcium phosphate mineral. The principal enzymes mediating these reactions, carbonic anhydrase and alkaline phosphatase, open novel targets for pharmacological intervention of bone diseases like osteoporosis, by applying compounds acting as potential activators of …
A Basis Set of Elementary Operations Captures Recombination of Neocortical Cell Assemblies During Basal Conditions and Learning
2019
Cell assemblies — subgroups within neuronal networks — are believed to serve as functional entities underlying cognitive capabilities such as categorical perception or memory formation and storage. However, little is known about their long-term dynamics. Using chronic in vivo calcium imaging in the mouse auditory cortex, we find that cell assemblies undergo continuous recombination, even under behaviorally stable conditions. We identify a basis set of elementary operations capturing the dynamics of cell assemblies, which involve plasticity of both the stimulus tuning of particular assemblies as well as the cellular composition of an assembly. Auditory fear conditioning introduces biases in …
Mechanisms of nitric-oxide-induced increase of free cytosolic Ca2+ concentration in Nicotiana plumbaginifolia cells.
2005
In this study, we investigated a role for nitric oxide (NO) in mediating the elevation of the free cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) in plants using Nicotiana plumbaginifolia cells expressing the Ca(2+) reporter apoaequorin. Hyperosmotic stress induced a fast increase of [Ca(2+)](cyt) which was strongly reduced by pretreating cell suspensions with the NO scavenger carboxy PTIO, indicating that NO mediates [Ca(2+)](cyt) changes in plant cells challenged by abiotic stress. Accordingly, treatment of transgenic N. plumbaginifolia cells with the NO donor diethylamine NONOate was followed by a transient increase of [Ca(2+)](cyt) sensitive to plasma membrane Ca(2+) channel inhibitors …
Staphylococcal alpha-toxin: repair of a calcium-impermeable pore in the target cell membrane
2000
Staphylococcal alpha-toxin forms heptameric pores that render membranes permeable for monovalent cations. The pore is formed by an amphipathic beta-barrel encompassing amino acid residues 118-140 of each subunit of the oligomer. Human fibroblasts are susceptible to alpha-toxin but are able to repair the membrane lesions. Thereby, toxin oligomers remain embedded in the plasma membrane and exposed to the extracellular medium. In this study, we sought to detect structural changes occurring in the pore-forming sequence during lesion repair. Single cysteine substitution mutants were labelled with the environmentally sensitive fluorochrome acrylodan and, after mixing with wild-type toxin, incorpo…
Dynamics of Ca2+ and guanosine 5'-[gamma-thio]triphosphate action on insulin secretion from alpha-toxin-permeabilized HIT-T15 cells.
1994
The time course of Ca2+ and GTP-analogue effects on insulin secretion was investigated in HIT-T15 cells permeabilized with Staphylococcus alpha-toxin. These cells responded to Ca2+ in the range 0.1-10 microM and could be used in a dynamic perifusion system because of the minimal run-down of the secretory response. High Ca2+ (10 microM) elicited a monophasic ATP-dependent stimulation of insulin secretion that reached a peak within 5 min (approximately 20-fold increase) and rapidly decreased during the subsequent 15 min to a plateau remaining above basal rates (0.1 microM Ca2+). The decrease in Ca(2+)-induced insulin secretion with time could not be attributed to decreased capacity to respond…
Interaction of Neuronal Calcium Sensor-1 (NCS-1) with Phosphatidylinositol 4-Kinase β Stimulates Lipid Kinase Activity and Affects Membrane Trafficki…
2001
Phosphatidylinositol 4-kinases (PI4K) catalyze the first step in the synthesis of phosphatidylinositol 4,5-bisphosphate, an important lipid regulator of several cellular functions. Here we show that the Ca(2+)-binding protein, neuronal calcium sensor-1 (NCS-1), can physically associate with the type III PI4Kbeta with functional consequences affecting the kinase. Recombinant PI4Kbeta, but not its glutathione S-transferase-fused form, showed enhanced PI kinase activity when incubated with recombinant NCS-1, but only if the latter was myristoylated. Similarly, in vitro translated NCS-1, but not its myristoylation-defective mutant, was found associated with recombinant- or in vitro translated P…
Hypersusceptibility of neutrophil granulocytes towards lethal action of free fatty acids contained in enzyme-modified atherogenic low density lipopro…
2008
Abstract Objective The bulk of LDL entrapped in the arterial intima is modified by hydrolytic enzymes, leading to extensive cleavage of cholesterylesters and liberation of fatty acids. The latter induce apoptosis in endothelial cells but are far less cytotoxic towards macrophages. We have compared the cytotoxic effects of enzymatically modified LDL (E-LDL) on macrophages and polymorphonuclear granulocytes (PMN). Methods and results E-LDL displayed toxicity towards PMN at far lower concentrations than towards monocyte-derived macrophages. Native or oxidized LDL had no effect. Free fatty acids contained in E-LDL were the cause of the observed toxicity, which could be mimicked by linoleic acid…
Soluble N-ethylmaleimide-sensitive-factor attachment protein and N-ethylmaleimide-insensitive factors are required for Ca2+-stimulated exocytosis of …
1996
Ca2+ stimulates exocytosis in permeabilized insulin-secreting cells. To investigate the putative cytosolic components involved in the Ca2+ response, HIT-T15 cells (a pancreatic B-cell line) were permeabilized with streptolysin-O, a procedure that allows rapid exchange of soluble components including macromolecules. We found that in this cell preparation the secretory response to Ca2+ but not to guanosine 5'-[gamma-thio]triphosphate was lost as a function of time and could be restored by rat brain cytosol in a concentration-dependent manner. Reconstitutive activity of rat brain cytosol was found in a high-molecular-mass heat-labile partially N-ethylmaleimide(NEM)-sensitive fraction. The NEM-…
Polyphosphate, the physiological metabolic fuel for corneal cells: a potential biomaterial for ocular surface repair
2019
The regeneration of the epithelium, covering the avascular cornea, involves the processes of differentiation, proliferation and migration of cells originating from the corneal epithelial stem cells. We ask the question if these energy-consuming processes can be fueled by the physiological, inorganic polyphosphate (polyP), the main energy storage/donor molecule in the extracellular space. The ex vivo results reveal that addition of polyP, in the form of soluble Na-polyP, to the culture medium elicits a strong stimulatory effect on cell viability/growth and migration of corneal epithelial cells. Microscopic analyses of partially denuded cornea specimens show that in the presence of polyP, but…