Calcium buffering capacity

The monoethanolamine-hydrochloric acid buffer has a buffering capacity equal to the ammonia-ammonium chloride buffer commonly employed for the titration of calcium and magnesium with EDTA and solochrome black (compare Section 10.54). The buffer has excellent keeping qualities, sharp end points are obtainable, and the strong ammonia solution is completely eliminated. 

Recent studies by Crompton et al. have shown that oxidant stress may open a Ca-sensitive, non-selective pore in the inner mitochondrial membrane that is blocked by cyclosporin A (Crompton, 1990 Crompton and Costi, 1990). This pore opening results in massive mitochondrial swelling, dissipation of the transmembrane proton gradient and disruption of mitochondrial energy production (Crompton et al., 1992). Since mitochondria may play a role as a slow, high-capacity cytosolic calcium buffer (Isenberg et al., 1993), disruption of mitochondrial function may also contribute to calcium overload and cell injury. 

During the lifetime of a root, considerable depletion of the available mineral nutrients (MN) in the rhizosphere is to be expected. This, in turn, will affect the equilibrium between available and unavailable forms of MN. For example, dissolution of insoluble calcium or iron phosphates may occur, clay-fixed ammonium or potassium may be released, and nonlabile forms of P associated with clay and sesquioxide surfaces may enter soil solution (10). Any or all of these conversions to available forms will act to buffer the soil solution concentrations and reduce the intensity of the depletion curves around the root. However, because they occur relatively slowly (e.g., over hours, days, or weeks), they cannot be accounted for in the buffer capacity term and have to be included as separate source (dCldl) terms in Eq. (8). Such source terms are likely to be highly soil specific and difficult to measure (11). Many rhizosphere modelers have chosen to ignore them altogether, either by dealing with soils in which they are of limited importance or by growing plants for relatively short periods of time, where their contribution is small. Where such terms have been included, it is common to find first-order kinetic equations being used to describe the rate of interconversion (12). 

When calcium carbonate goes into solution, it releases basic carbonate ions (COf ), which react with hydrogen ions to form carbon dioxide (which will normally remain in solution at deep-well-injection pressures) and water. Removal of hydrogen ions raises the pH of the solution. However, aqueous carbon dioxide serves to buffer the solution (i.e., re-forms carbonic acid in reaction with water to add H+ ions to solution). Consequently, the buffering capacity of the solution must be exceeded before complete neutralization will take place. Nitric acid can react with certain alcohols and ketones under increased pressure to increase the pH of the solution, and this reaction was proposed by Goolsby41 to explain the lower-than-expected level of calcium ions in backflowed waste at the Monsanto waste injection facility in Florida. 

The functions of the calcium-storage capacity of the ER are at least threefold the association of Ca2+ with Ca2+-binding proteins in the ER is part of a chaperone function that is essential for normal protein synthesis the rapid rate of Ca2+ uptake by endoplasmic pumps provides shortterm cytoplasmic Ca2+ buffering that resists untoward and transient changes in [Ca2+] and, finally, many signaling pathways employ elevated [Ca2+] to activate physiological processes. Extensive Ca2+ release from ER is coupled to activation of Ca2+ entry across the plasma membrane, a process known as capacitative calcium entry, which is discussed below. 

Selected entries from Methods in Enzymology [vol, page(s)] Chelation, 238, 74, 76, 297 buffers [for analysis of exocytosis, 221, 132 preparation, 219, 186 modulation of cytosolic buffering capacity with quin2, 221, 159] fluorescence assay, 240, 724-725, 740-742 fluorescence imaging, 225, 531 238, 303-304, 322-325, 334-335 free intracellular levels after bacterial invasion, 236, 482-489 free calcium in solutions for membrane fusion analysis, calculation and control, 221, 149 homeostasis mechanisms, 238, 80 hormonal elevation, 238, 79 inositol phosphate effect on release, 238, 207 determination of cytosolic levels [computer methods, 238, 73-75 with fura-2, 238, 73, 146 with indo-1, 238, 298, 316-317 with quin-2, 238, 297] hormone effects, 238, 79 ionomycin effects, 238, 79 membrane depolarization effects,... 

The symbols (g) and (7) in this equation indicate that the species shown, CO2 and H2O, exist as a gas and a liquid, respectively.) The removal of hydrogen ions by calcium carbonate tends to protect the lake from an increase in acidity. By contrast, lakes that are embedded in granite rock do not have this buffering capacity. They tend to become more acidic than do limestone lakes when exposed to the same level of acid deposition. 

Acid rain has resulted in the loss of life in a number of lakes. The ability of a lake to withstand the impacts of acid rain is related to the geology of the lake s basin. In areas with limestone (calcium carbonate) deposits, a lake has a natural buffering capacity. The buffering capacity refers to the ability to resist changes in pH. In well-buffered lakes, calcium carbonate reacts... 

Differences in pH and buffering capacity among individual lots of fresh milk reflect compositional variations arising from the functions of the mammary gland. In general the pH is lower in colostrum (down to pH 6.0 McIntyre et al. 1952) and higher in cases of mastitis (up to pH 7.5 Prouty 1940) than in normal milk of mid-lactation. As discussed in Chapter 1, colostrum and mastitis milks are known to differ radically in their proportions of the proteins and certain salts. Milks of lower phosphorus, casein, and Ca2+ tend to be low in titratable acidity, while excessive acidity is related to hyperketonemia, inadequate calcium and excessive concentrates in the ration (Bonomi 1978). 

In principle, it would be logical to combine plots of the buffer index curves of each of the buffer components of milk and thus obtain a plot which could be compared with that actually found for milk. It is not difficult, of course, to conclude that the principal buffer components are phosphate, citrate, bicarbonate, and proteins, but quantitative assignment of the buffer capacity to these components proves to be rather difficult. This problem arises primarily from the presence of calcium and magnesium in the system. These alkaline earths are present as free ions as soluble, undissociated complexes with phosphates, citrate, and casein and as colloidal phosphates associated with casein. Thus precise definition of the ionic equilibria in milk becomes rather complicated. It is difficult to obtain ratios for the various physical states of some of the components, even in simple systems. Some concentrations must be calculated from the dissociation constants, whose... 

Similarly, cooling water that is fully softened tends to lack sufficient buffering capacity and creates the potential for significant corrosion within the cooling system, so care and attention to design detail are needed if future corrosion problems are to be avoided. Also, most chemical treatments incorporate polymers or phosphonates of some sort to provide a measure of corrosion inhibition. These products usually require the presence of at least 25 to 35 ppm of calcium hardness to provide satisfactory inhibition. 

Separates aqueous phase without altering the ionic composition. Principally applied in studies on calcium and phosphate in cheese, buffering capacity, lysis of starter cultures Commonly used to extract short peptides and amino acids. Suitable for bacterially ripened cheeses... 

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