Free calcium

The industrial process for preparing the reagent usually permits a little hydrolysis to occur, and the product may contain a little free calcium hydroxide or basic chloride. It cannot therefore be employed for drying acids or acidic liquids. Calcium chloride combines with alcohols, phenols, amines, amino-acids, amides, ketones, and some aldehydes and esters, and thus cannot be used with these classes of compounds. 

In addition to the main acidulation reaction, other reactions also occur. Free calcium carbonate in the rock reacts with the acid to produce additional by-product calcium compounds and CO2 gas which causes foaming. Other mineral impurities, eg, Fe, Al, Mg, U, and organic matter, dissolve, the result being that the wet-process acid is highly impure. 

Calcium metal was produced in 1855 by electrolysis of a mixture of calcium, strontium, and ammonium chlorides, but the product was highly contaminated with chlorides (1). By 1904 fairly large quantities of calcium were obtained by the electrolysis of molten calcium chloride held at a temperature above the melting point of the salt but below the melting point of calcium metal. An iron cathode just touched the surface of the bath and was raised slowly as the relatively chloride-free calcium solidified on the end. This process became the basis for commercial production of calcium metal until World War II. 

The Ca(Il) coaceatratioa ia blood is closely coatroUed aormal values He betweea 2.1 and 2.6 mmol/L (8.5—10.4 mg/dL) of semm (21). The free calcium ion concentration is near 1.2 mmol/L the rest is chelated with blood proteias or, to a lesser extent, with citrate. It is the free Ca(Il) ia the semm that determines the calcium balance with the tissues. The mineral phase of bone is essentially ia chemical equiUbrium with calcium and phosphate ions present ia blood semm, and bone cells can easily promote either the deposition or dissolution of the mineral phase by localized changes ia pH or chelating... 

Calcium is the trigger behind the muscle contraction process (24,25). Neural stimulation activates the release of stored Ca(Il) resulting in a dramatic increase in free calcium ion levels. The subsequent binding of Ca(Il) resulting in a dramatic increase in free calcium ion levels. The subsequent binding of Ca(Il) to the muscle protein troponin C provides the impetus for a conformational change in the troponin complex and sets off successive events resulting in muscle contraction. 

These ate the main reactions ia Pordand cements because the two calcium siHcates constitute about 75% of the cement. The average lime—silica ratio (C S) may vary from about 1.5 to about 2.0 or even higher, the average value is about 1.7. The water content varies with the ambient humidity, the three moles of water being estimated from measurements ia the dry state and stmctural considerations. As the lime—silica ratio of the C—S—H iacreases, the amount of water iacreases on an equimolar basis, ie, the lime goes iato the stmcture as calcium hydroxide, resulting ialess free calcium hydroxide. 

BuHders, eg, sodium triphosphate and nonphosphate buHders such as zeoHte and citrate, remove free calcium from the washing solution. 

Excitation of smooth muscle via alpha-1 receptors (eg, in the utems, vascular smooth muscle) is accompanied by an increase in intraceUular-free calcium, possibly by stimulation of phosphoUpase C which accelerates the breakdown of polyphosphoinositides to form the second messengers inositol triphosphate (IP3) and diacylglycerol (DAG). IP3 releases intracellular calcium, and DAG, by activation of protein kinase C, may also contribute to signal transduction. In addition, it is also thought that alpha-1 adrenergic receptors may be coupled to another second messenger, a pertussis toxin-sensitive G-protein that mediates the translocation of extracellular calcium. 

Notes. (1) The usefulness of the HHSNNA indicator for the titration of calcium depends upon the fact that the pH of the solution is sufficiently high to ensure the quantitative precipitation of the magnesium as hydroxide and that calcium forms a more stable complex with EDTA than does magnesium. The EDTA does not react with magnesium [present as Mg(OH)2] until all the free calcium and the calcium-indicator complex have been complexed by the EDTA. If the indicator is added before the potassium hydroxide, a satisfactory end-point is not obtained because magnesium salts form a lake with the indicator as the pH increases and the magnesium indicator-lake is co-precipitated with the magnesium hydroxide. 

Either the Mohr titration or the adsorption indicator method may be used for the determination of chlorides in neutral solution by titration with standard 0.1M silver nitrate. If the solution is acid, neutralisation may be effected with chloride-free calcium carbonate, sodium tetraborate, or sodium hydrogencarbonate. Mineral acid may also be removed by neutralising most ofthe acid with ammonia solution and then adding an excess of ammonium acetate. Titration of the neutral solution, prepared with calcium carbonate, by the adsorption indicator method is rendered easier by the addition of 5 mL of 2 per cent dextrin solution this offsets the coagulating effect of the calcium ion. If the solution is basic, it may be neutralised with chloride-free nitric acid, using phenolphthalein as indicator. 

Cobbold, P. H. (1980). Cytoplasmic free calcium and amoeboid movement. Nature 285 441 146. 

Miller, A. L., et al. (1991). Imaging free calcium in cultured Aplysia bag cell neurons. Biol. Bull. 181 325. 

Shimomura, O., and Johnson, F. H. (1979a). Chemistry of the calcium-sensitive photoprotein aequorin. In Ashley, C. C., and Campbell, A. K. (eds.), Detection and Measurement of Free Calcium Ions in Cells, pp. 73-83. Elsevier/North-Holland, Amsterdam. 

Regulation of Intracellular Free Calcium Concentration (an n-Compartment System) 183... 

Although in in vivo circumstances an intracellular free calcium increase apparently acts as the primary modulator of contraction, it can be bypassed in highly permeabilized smooth muscle preparations where the active subunit of MLCK can be introduced to phosphorylate myosin and induce contraction. The MLCK catalyzed phosphorylation of serine-19 is seen as the necessary event in the activation of smooth muscle myosin to form crossbridges. Thus, the rising phase of force during an isometric smooth muscle contraction follows an increase in the degree of phosphorylation of myosin, and that in turn follows the transient rise of (a) cytosolic free Ca, (b) Ca-calmodulin complexes, and (c) the active form of MLCK. The regulation of the intracellular calcium is discussed below. The dynam-... 

Plasma membrane channels. The most common mechanism for the movement of into smooth muscle cells Ifom the extracellular space is the electrodiffusion of Ca " ions through highly selective channels. This movement can be significant in two quite different ways. First, Ca ions carry two positive charges and, in fact, most of the inward charge movement across the plasma membrane of smooth muscle myocytes is carried by Ca. Most smooth muscle action potentials are known to be Ca " action potentials. And second, the concentration of intracellular free calcium, the second messenger, is increased by inward calcium movement. 

Figure 1. Original records of tension and intracellular free calcium concentration Caf ) obtained from a single mouse muscle fiber during a fatigue run (modified from Westerblad and Allen, 1991). A continuous tension record in which each vertical line represents a tetanus. B (Ca ] (measured with fura-2) and tension records obtained from the individual tetani (a, b, and c) indicated above the record in A. Three major features are illustrated 1.) the initial tension decline is accompanied by an increase in tetanic ICa li, 2.) late in fatigue the tetanic [Ca li is reduced, and 3.) the resting [Ca li increases during fatiguing stimulation (dashed line indicates resting [Ca ] in control). Stimulation periods are shown below tension records in B. From Westerblad et al., 1991, with permission from the Amer. Physiol. Society.

Neutrophils represent an ideal system for studying osmotic effects on exocytosis. Stimulation of cytochalasin-B-treated neutrophils with the chemotactic peptide Jlf-formylmethionyl-leucyl-phenyl-alanine (FMLP) results in a rapid compound exocytosis up to 80% of lysosomal enzymes are released within 30 s (9-14). Secretion appears to be triggered by a rise in the level of cytosolic free calcium (15-18) promoted in part by entry of extracellular calcium through receptor-gated channels and in part by release of calcium that is sequestered or bound at some intracellular site (19-21). In this presentation, we augment our previously published data (22,23), which demonstrates that lysosomal enzyme release from neutrophils is inhibited under hyperosmotic conditions and that the rise in cytosolic calcium preceding secretion is inhibited as well. 

Figure 2. Reporting of cytosolic free calcium levels by indo-1. Increases in cytosolic calcium, due either to entry of extracellular calcium via calcium channels or to release of intracellular calcium sequestered in organelles such as smooth endoplasmic reticulum, results in formation of the indo-l-calcium complex. Fluorescence intensity at 400 nm (excitation at 340 nm) is proportional to the concentration of this complex the dissociation constant for this complex is about 250 nff (24), making this probe useful for detecting calcium activities in the range of 25 to 2500 nJ. ...

How pectic signals were transduced was unknown, but information suggested that cytosolic free Ca might be involved [22]. Fluorescence ratio imaging has then been used to follow the evolution of free calcium concentrations ([Ca " ] ) after stimulation of carrot protoplasts by oligogalacturonides [23]. 

Figure 12. Binding of calcium ions by pectate and apple pectin, measured by equilibrium dialysis gainst citrate to buffer the concentration of free calcium ions at low levels.

Table 6. Free calcium concentrations in equilibrium with common complexing agents. A low free calcium concentration implies effective complexation, whether the complex formed is soluble or insoluble. The data were derived from either stability constants (soluble complexes) or solubility products (insoluble complexes).

Hydrolytic decomposition of these cements is clinically advantageous. Free calcium hydroxide is present in excess so that large amounts of calcium are released which, together with high alkalinity, promotes... 

The modification of bentonite with alkylsilanes improves the dispersing properties [991]. Incorporation of phosphonate-type compounds in bentonites for drilling mud permits the blockage of free calcium ions in the form of soluble and stable complexes and the preservation or restoration of the initial fluidity of the mud [1222]. The phosphonates also have dispersing and fluidizing effects on the mud. 

Kanerud, L., Hafttrom, 1. and Ringertz, B. (1990). Effect of sulphasalazine and sulphapyridine on neutrophil superoxide production role of cytosolic free calcium. Ann. Rheum. Dis. 49, 296-300. 

Ca The chemical symbol far calcium [Ca li Intracellular free calcium concentration... 

For acute symptomatic hypocalcemia, 200 to 300 mg of elemental calcium is administered IV and repeated until symptoms are fully controlled. This is achieved by infusing 1 g of calcium chloride or 2 to 3 grams of calcium at a rate no faster than 30 to 60 mg of elemental calcium per minute. More rapid administration is associated with hypotension, bradycardia, or cardiac asystole. Total calcium concentration is commonly monitored in critically ill patients. Under normal circumstances, about half of calcium is loosely bound to serum proteins while the other half is free. Total calcium concentration measures bound and free calcium. Ionized calcium measures free calcium only. Under usual circumstances, a normal calcium level implies a normal free ionized calcium level. Ionized calcium should be obtained in patients with comorbid conditions that would lead to inconsistency between total calcium and free serum calcium (abnormal albumin, protein, or immunoglobulin concentrations). For chronic asymptomatic hypocalcemia, oral calcium supplements are given at doses of 2 to 4 g/day of elemental calcium. Many patients with calcium deficiency have concurrent vitamin D deficiency that must also be corrected in order to restore calcium homeostasis.2,37,38... 

Calcium salt. Calcium gluconate is the preferred salt in PN because it is has a low dissociation in solution with lesser free calcium available at a given time to bind phosphate (as opposed to calcium chloride, which dissociates rapidly in solution). 

The interest in colour indicators has recently increased as they are used for the direct determination of pH (acid-base indicators) and free calcium ions (fluorescent derivatives based on the calcium chelator EGTA as metallochromic indicators) in biological systems at cellular level. 

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