Source Of Calcium Ions Research Articles

Meat & bone meal extract and gelatin as renewable flocculants

Readily available proteins were tested as renewable flocculants, and their actions were compared to that of anionic PAM, a common, commercial flocculant that requires the coaddition of a calcium ion source. Two soy proteins, a whey fraction, a porcine gelatin, and a meat & bone meal (MBM) extract were used in the flocculation test. It was found that MBM extract and porcine gelatin promoted clay flocculation, and flocculation was complete by 24 h with or without the addition of calcium chloride. The other tested proteins did not promote clay flocculation, but all of the proteins were found to be adsorbed to clay. The protein adsorptions were well described by the Langmuir model, and gelatin and MBM extract had higher maximum adsorption capacities than the other proteins. Zwitterionic buffer solutions at pH 5.5, 7.0, and 10.0 were tested in the flocculation experiments. Addition of the pH 5.5 buffer caused the two soy proteins to become clay flocculants and lowered the concentration of gelatin and MBM extract necessary to promote complete flocculation by 24 h. Calcium chloride was not required for flocculation. Under optimal testing conditions, the dried weight of gelatin or MBM extract was 2.6 and 17 times higher, respectively, than the weight of anionic PAM required for complete flocculation at 24 h.

FORMATION OF METASTABLE VATERITE CRYSTALS IN A POLYMER MATRIX BY GASEOUS DIFFUSION

A composite consisting of a polymer and calcium carbonate has been synthesized by allowing carbon dioxide to diffuse into a poly(ethylene oxide) film containing a source of calcium ions. The X-ray pattern of the synthetic composite material shows that the least thermodynamically stable polymorph of calcium carbonate, vaterite is the mineral phase which is formed, rather than the most thermodynamically stable calcite phase. This effect has been seen in other reports of crystallization of inorganic phases which have been mediated by a polymer matrix and/or other organic moieties. In this paper, some possible explanations are presented which may help explain this phenomenon.

Bone graft substitutes

Surgeons involved in skeletal repair, reconstruction, and oncology commonly encounter or create bone defects that are unlikely to heal if treated by fixation alone. Cancellous and cortical autografts have been used for decades to treat skeletal defects, but the amount of autograft is limited, and morbidity related to autograft harvesting can be considerable. Allograft can “extend” autograft, but has limited biological and mechanical properties, carries with it the potential for disease transmission, and has not been accepted for other reasons in some societies. The need for autograft substitutes has led to the development of a wide variety of skeletal substitute materials that are being introduced rapidly into skeletal surgery and are thus likely to be visualized with increasing frequency by radiologists and pathologists. These materials vary with respect to composition, biologic properties, mechanical strength, and radiographic appearance. Several important terms have been developed to describe the biologic properties of bone graft substitute/extender materials [1–3]. A material is osteoconductive if, due to its composition, shape, or surface texture, it promotes bone formation along its surface when it is placed into bone. Purely osteoconductive materials, such as hydroxyapatite, are usually not associated with bone formation when placed outside bone. A material is osteoinductive if it induces bone to form when placed into an extraskeletal site, usually by inducing stromal cells to differentiate into osteoblasts or osteoblast precursors. Osteoinductive materials, such as demineralized bone matrix or selected bone morphogenetic proteins, also form bone within the skeleton, but, as originally defined by Marshal Urist, a material is demonstrated to be osteoinductive by the formation of bone in an extraskeletal site such as skeletal muscle. A material is osteogenic if it causes bone formation because of the implantation of viable cells, such as autograft, aspirated or enriched bone marrow osteoprogenitor cells, or by the combination of those cells and some other synthetic substrate. While these three terms are thought to describe the principal mechanisms of many bone graft substitute materials, other mechanisms of enhancing bone formation also exist, such as the simple provision of a local source of calcium ions that, by re-precipitation as a carbonated apatite, may serve as a nidus for bone mineralization. Some investigators have introduced terms such as “osteopromotive” or “osteostimulatory” into the literature, in part via marketing studies, and they use those terms to imply enhanced bone formation by some other, usually undefined (and sometimes mythical), mechanism. It should also be noted that the terms osteoconductive, osteoinductive, and osteogenic are relative, not absolute. Bone graft materials can be classified in many different ways, including based on composition, biologic or mechanical properties, cost, or radiographic appearance. The table inserted below is not comprehensive, but it lists some examples of bone graft substitutes/extenders according to composition (Table 1). The appearance of these materials on imaging studies depends on the composition of the material, the extent to which it has become “incorporated” into bone, and, of course, the nature of the imaging study itself. It is important for radiologists to recognize that some of the preparations of bone graft substitutes are mineralized, or partially mineralized, at the time they are inserted into the bone. Skeletal Radiol (2007) 36:1105–1107 DOI 10.1007/s00256-007-0377-4

Endogenous Circannual Clock and HP Complex in a Hibernation Control System

Hibernation in mammals is a mysterious biological phenomenon that appears on a seasonal basis for surviving a potentially lethal low body temperature (Tb) near 0 degrees C and protecting organisms from various diseases and harmful events during hibernation. The exact mechanism by which such a unique ability is seasonally developed is still unknown. On the basis of our previous finding that the source of calcium ions for excitation-contraction coupling in myocardium of chipmunks, a rodent hibernator, is seasonally modulated for hibernation, the liver-derived hibernation-specific protein (HP) complex was discovered. Recently, the HP complex was identified as a promising candidate hormone that carries a hibernation signal to the brain independently of Tb and environmental changes for developing a capacity for tolerating low Tb. This finding will promote new approaches to understanding biological hibernation systems, including a circannual clock and its signaling pathway between the brain and the periphery. A new definition of hibernation and a possible model of a hibernation control system are proposed.

Effect of mineral trioxide aggregate on proliferation of cultured human dental pulp cells

To investigate the effect of mineral trioxide aggregate (MTA) on the proliferation of human dental pulp (HDP) cells ex-vivo. Human dental pulp cells were cultured with MTA or calcium hydroxide-containing cement (Dycal) using culture plate inserts. Control cells were cultured with culture plate inserts only. Cell proliferation was measured for up to 14 days using a Cell Counting kit, and the concentration of calcium ions released from the tested materials was assessed using a Calcium E-test kit. To confirm that the effect of MTA was attributable to released calcium ions, cell proliferation was measured in the presence of exogenous calcium chloride as a source of calcium ions while in the absence of MTA. Mineral trioxide aggregate significantly stimulated cell proliferation after 12 days, whereas Dycal had no such effect. The number of calcium ions released from MTA was significantly higher than that released from Dycal. Following the addition of calcium chloride, cell proliferation increased in a dose-dependent manner after 12 days. Moreover, cell proliferation showed a similar pattern whether a given concentration of calcium ions was produced by calcium chloride or by release from MTA. In this ex-vivo study, the elution components such as calcium ions from MTA had higher proliferation ability of HDP cells than control and Dycal.

Calcium hydroxyapatite, Ca 10(PO 4) 6(OH) 2 ceramics prepared by aqueous sol–gel processing

Aqueous sol–gel chemistry routes based on ammonium–hydrogen phosphate as the phosphorus precursor and calcium acetate monohydrate as source of calcium ions have been developed to prepare calcium hydroxyapatite samples with different morphological properties. In the sol–gel processes, an aqueous solutions of ethylene diamine tetra-acetic acid (EDTA) or tartaric acid (TA) as complexing agents were added to the reaction mixture. The monophasic Ca 10(PO 4) 6(OH) 2 samples were obtained by calcination of precursor gels for 5 h at 1000 °C. The phase transformations, composition and micro-structural features in the polycrystalline samples were studied by thermoanalytical methods (TGA/DTA), infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD) and scanning electron microscopy (SEM). It was shown that adjusting the nature of complexing agent in the aqueous sol–gel processing can be used to control the morphology of the ceramic samples.

Alginate rafts and their characterisation

Alginate/antacid anti-reflux preparations are designed to provide symptom relief by forming a physical barrier on top of the stomach contents in the form of a neutral floating gel or raft. This study tested the in vitro effectiveness of a range of liquid products in forming rafts that were cohesive, buoyant, voluminous, resistant to reflux and durable under conditions of movement (resilient). The products tested had a wide range of acid neutralising capacities (ANCs). It was found that products with a high ANC and no calcium ion source formed rafts of low strength, weight and volume, which appeared more as floating precipitates than coherent gels. Products with a high ANC and a calcium ion source formed medium strength, weight and volume rafts. Products with a low ANC formed strong coherent rafts with medium to large weight and volume, and those with low ANC and a calcium ion source formed the strongest rafts. Products with stronger rafts were found to be more resilient and more resistant to reflux in an in vitro reflux model. Significant overall differences in raft buoyancy were found between products forming coherent rafts but these could not be related to the product formulation or amount of available carbon dioxide.

Plasticity of calcium channels in dendritic spines.

Voltage-sensitive Ca2+ channels (VSCCs) constitute a major source of calcium ions in dendritic spines, but their function is unknown. Here we show that R-type VSCCs in spines of rat CA1 pyramidal neurons are depressed for at least 30 min after brief trains of back-propagating action potentials. Populations of channels in single spines are depressed stochastically and synchronously, independent of channels in the parent dendrite and other spines, implying that depression is the result of signaling restricted to individual spines. Induction of VSCC depression blocks theta-burst-induced long-term potentiation (LTP), indicating that postsynaptic action potentials can modulate synaptic plasticity by tuning VSCCs. Induction of depression requires [Ca2+] elevations and activation of L-type VSCCs, which activate Ca2+/calmodulin-dependent kinase II (CaMKII) and a cyclic adenosine monophosphate (cAMP)-dependent pathway. Given that L-type VSCCs do not contribute measurably to Ca2+ influx in spines, they must activate downstream effectors either directly through voltage-dependent conformational changes or via [Ca2+] microdomains.

Validity of the rapid buffering approximation near a point source of calcium ions

In the presence of rapid buffers the full reaction-diffusion equations describing Ca2+ transport can be reduced using the rapid buffering approximation to a single transport equation for [Ca2+]. Here we simulate the full and reduced equations, exploring the conditions necessary for the validity of the rapid buffering approximation for an isolated Ca2+ channel or a cluster of channels. Using a point source and performing numerical simulations of different durations, we quantify the error of the rapid buffering approximation as a function of buffer and source parameters as well as the time and spatial scale set by the resolution of confocal microscopic measurements. We carry out simulations of Ca2+ "sparks" and "puffs," both with and without the indicator dye Ca2+ Green-1, and find that the rapid buffering approximation is excellent. These calculations also show that the traditional calculation of [Ca2+] from a fluorescence signal may grossly underestimate the true value of [Ca2+] near a source. Finally, we use the full model to simulate the transient Ca2+ domain near the pore of an open Ca2+ channel in a cell dialyzed with millimolar concentrations of 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid or EGTA. In this regime, where the rapid buffering approximation is poor. Neher's equation for the steady-state Ca2+ profile is shown to be a reliable approximation adjacent to the pore.

A low-current discharge source for calcium ions

A low-power discharge source of calcium ions is discussed. The voltage-current characteristics of this source under different experimental conditions are presented. The population transfer between the lowest metastable states of the neutral calcium (Ca I) and the resonance states of Ca II is investigated through a study of spectral emission. The results may be of interest in the spectroscopy of metallic ions as well as for metal vapour lasers utilizing ionic transitions.

Crosslinking Kinetics of Thermally Preset Alginate Gels

ABSTRACTThe Sharp‐Interface model was used to describe the crosslinking kinetics of thermally preset calcium alginate gel at constant temperature. The model assumes diffusion of calcium ions through a preformed gel of sodium alginate and a selected carrier, and an instantaneous reaction between the calcium and sodium alginate. The proposed model was experimentally verified using two different carriers at the following concentrations: agar 0.6(g/100 mL)‐0.8(g/100 mL), and gelatine 4(g/100 mL); sodium alginate concentrations were 1(g/100 mL) and 1.5(g/100 mL), while a 2(g/100 mL) calcium lactate solution was used as calcium ion source. The diffusion coefficient of calcium ion was determined using a cell diffusion model. The model can be used to predict processing effects on food gels.

Elicitor-stimulated benzophenanthridine alkaloid biosynthesis in bloodroot suspension cultures is mediated by calcium

Addition of an elicitor derived from the fungus Penicillium expansum Link (PE-elicitor) or the calcium ionophore A23187, to a suspension-cell culture of Sanguinaria canadensis induced the production of the benzophenanthridine alkaloids, sanguinarine and chelerythrine, in a dose-dependent manner. Pretreatment of the cells with the specific calcium chelatant EGTA (3 mM) or the calcium channel inhibitor verapamil (100 μM), for 1 hr prior to the addition of the PE-elicitor, decreased the accumulation of both sanguinarine and chelerythrine. Moreover, A23187-stimulated alkaloid accumulation was almost completely inhibited by pretreating the suspension cells with EGTA (3 mM) for 1 hr and this suppression was reversed by the readdition of calcium ions to the medium. Furthermore, addition of trifluoperazine (100 μM) to the suspension-cell cultures 1 hr before the PE-elicitor (35 μg Glc equ ml −1) treatment suppressed the accumulation of benzophenanthridine alkaloids by 51% as compared to suspension cells treated with PE-elicitor alone. These results demonstrate that an external source of calcium ions is required for elicitor-induced benzophenanthridine alkaloid accumulation and suggest that calcium and possibly calmodulin and/or protein kinase C may participate in a signal transduction system that mediates this process.

Rhizoliths in ancient eolianites

Rhizoliths are abundant within Permo-Pennsylvanian eolian rocks of southeastern Utah. They are also present at the tops of several eolian sand bodies within the Pennsylvanian Fountain Formation of southeastern Wyoming and at a single stratigraphic level within the Jurassic Navajo Sandstone of southeastern Utah. Ranging in diameter from less than 1 mm to 15 cm, these cylindrical structures are composed of siliciclastic-free micrite and calcite spar. Cylinders ramify throughout the uppermost 2–3 m of thin, flat-topped sand bodies. Large cylinders are compound rhizoliths and display alveolar fabric, a feature resulting from rootlet calcification that is characteristic of modern and ancient calcretes. Development of rhizoliths required flat, geomorphically stable substrates for plant growth, highly permeable surficial sediments, and sources of calcium ions. The restriction of rhizoliths to planar deflation surfaces suggests that plants were unable to colonize or stabilize eolian bedforms. Paleozoic rhizoliths appear to be restricted to coastal areas with onshore winds. Associated evaporites suggest an arid to semi-arid paleoclimate. Rhizoliths formed when carbonate allochems derived from an upwind epeiric sea were dissolved and calcite reprecipitated around plant roots. Quaternary rhizoliths are best developed in similar sedimentologic and geographic settings. The abundance of rhizoliths and carbonate allochems in Quaternary and late Paleozoic low-latitude coastal dunes suggests that they are genetically related to glacio-eustatic sea-level fluctuations.

Influence of calcium-entry blockade on vasoconstrictor responses in feline mesenteric vascular bed.

The subtypes of postjunctional alpha-adrenoceptors activated by neuronally released and exogenous norepinephrine and the source of calcium used for vasoconstrictor responses were investigated in the feline mesenteric vascular bed. Under constant flow conditions, intra-arterial injections of phenylephrine and UK14304, alpha 1- and alpha 2-adrenoceptor agonists, increased mesenteric arterial perfusion pressure in a dose-related manner. Prazosin, an alpha 1-antagonist, reduced vasoconstrictor responses to phenylephrine without altering responses to UK14304. Yohimbine, an alpha 2-antagonist, reduced responses to UK14304 without altering responses to phenylephrine. The same pattern of blockade was observed in animals pretreated with 6-hydroxydopamine to destroy the integrity of adrenergic terminals. Responses to phenylephrine and UK14304 were reduced by nitrendipine, a calcium-entry blocking agent, and this agent decreased vasoconstrictor responses to sympathetic nerve stimulation, tyramine, and norepinephrine. Responses to sympathetic nerve stimulation were selectively blocked by prazosin, but responses to norepinephrine were selectively blocked by yohimbine. Vasoconstrictor responses to tyramine were reduced by both prazosin and yohimbine. Nitrendipine also reduced responses to angiotensin II, U46619, a prostaglandin endoperoxide analogue, Bay K 8644, and potassium chloride. These data suggest the presence of alpha 1- and postjunctional alpha 2-adrenoceptors and support the hypothesis that norepinephrine released by nerve excitation acts mainly on alpha 1-receptors but that exogenous norepinephrine acts primarily on alpha 2-receptors. However, norepinephrine released by tyramine acts on both receptor subtypes. Nitrendipine inhibited responses to the alpha 1- and alpha 2-adrenoceptor agonists as well as those to nerve released and exogenous norepinephrine, the calcium agonist, Bay K 8644, and to other vasoconstrictor agents. These data suggest that in the feline mesenteric vascular bed, an extracellular source of calcium ions is required for vasoconstriction induced by a variety of mechanisms including activation of alpha 1- and postjunctional alpha 2-adrenoceptors.

Phosphoprotein particles: calcium and inorganic phosphate binding structures.

Phosphoprotein particles were isolated in their native state from the physiological fluid of the estuarine clam Rangia cuneata , and the characteristics of the mineral ion-protein complex which constitutes the native particle were investigated by using mineral ion binding and mineral ion exchange techniques. The particles are aspartic acid rich, highly phosphorylated proteins containing calcium, magnesium, and inorganic phosphate ions and covalently cross-linked via histidinoalanine residues. Twenty-nine percent of the amino acid residues are phosphorylated. In their native state, the particles contain a protected pool of calcium and inorganic phosphate ions and an exchangeable pool of calcium and magnesium ions. The Ca/PO4 ratio in the protected pool is about 2.5. The number of binding sites for the protected mineral is unknown, but on the average, the native particles contain about 0.2 inorganic phosphate ion per organic phosphate residue. There is 1.0 exchangeable metal ion binding site per organic phosphate residue, and there is probably a phosphoserine residue at each site. These sites bind calcium with an apparent binding constant (KCa) of 4 X 10(3) M-1 at 50% saturation under physiological conditions, and KCa/ KMg is about 1.6. In vivo, about 85% of the exchangeable sites are occupied. The total number of calcium ion binding sites (N) in the phosphoprotein particles is related to the number of organic phosphate residues (Po) and the number of bound inorganic phosphate ions (Pi) by the equation N = Po + 2. 5Pi . The phosphoprotein particles probably serve as both the transporter and reserve source of calcium ions for shell development.

Encystment ofAzotobacter vinelandii in liquid culture

Cyst formation in liquid cultures ofAzotobacter vinelandii could be raised to 90% by including 0.6% CaCO3 in the Burk's basal salts solution. The cysts were resistant to desiccation and possessed exine and intine capsular components when observed by electron microscopy of ultrathin sections. Cells grown in liquid medium containing no CaCO3, but in which the pH was controlled by addition of 0.1m KOH, were not resistant to desiccation. The capsular material was loosely aggregated and not organized into the typical coat structure. The culture supernatant fluid became viscous and could be precipitated with CaCl2, yielding a thick, polysaccharide-like gel. Calcium carbonate in the liquid encystment medium served both as a means of acid neutralization and as a source of calcium ions. Calcium ions appear to be structural units necessary for coordination of the coat components into the rigid cyst structure. Other metal ions examined could not substitute effectively for calcium in the encysting system.