Plasma calcium levels, stability

In regards to necrosis, it is clear that the old adage an ounce of prevention is worth a pound of cure applies. Agents that stabilize ion homeostasis have proved to be effective in preventing necrosis in cell culture studies. For example, drugs that activate plasma membrane potassium ion channels or chloride ion channels can prevent membrane depolarization and so inhibit sodium and calcium ion influx. Agents that prevent large sustained increases in intracellular free calcium levels can also prevent neuronal... 

IV. It may be noted that although the concentration of ionic calcium has decreased only somewhat (from a normal range of about 49-52% to a level of 45%) there has been a redistribution of the non-ionic calcium from the plasma proteins to NTA. It can be anticipated for other chelates that the extent of this redistribution will be dependent upon the stability constants of the calcium chelates at phasma pH. Data for the effect of up to 1.5 M NTA on the ionic calcium level of plasma is provided in Figure 2. If... 

The extreme stability of the plasma calcium concentration is illustrated by the fact that, when an amount of calcium greater than that normally present in the whole of the extracellular fluids was injected into experimental animals, there was only a transient increase in the plasma calcium concentration, even though only half of the calcium was excreted during the experimental period. Conversely, alternate bleeding of experimental animals and transfusion with calcium-free blood merely causes a hypocalcaemia of short duration. Such experiments show that very efficient mechanisms exist for adding calcium to blood when the level falls and removing it when the level rises. 

Calcium-selective electrodes have long been in use for the estimation of calcium concentrations - early applications included their use in complexometric titrations, especially of calcium in the presence of magnesium (42). Subsequently they have found use in a variety of systems, particularly for determining stability constants. Examples include determinations for ligands such as chloride, nitrate, acetate, and malonate (mal) (43), several diazacrown ethers (44,45), and methyl aldofuranosides (46). Other applications have included the estimation of Ca2+ levels in blood plasma (47) and in human hair (where the results compared satisfactorily with those from neutron activation analysis) (48). Ion-selective electrodes based on carboxylic polyether ionophores are mentioned in Section IV.B below. Though calcium-selective electrodes are convenient they are not particularly sensitive, and have slow response times. 

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