Blood plasma, metal ions

Medical Uses. Citric acid and citrate salts are used to buffer a wide range of pharmaceuticals at their optimum pH for stabiUty and effectiveness (65—74). Effervescent formulations use citric acid and bicarbonate to provide rapid dissolution of active ingredients and improve palatabiUty. Citrates are used to chelate trace metal ions, preventing degradation of ingredients. Citrates are used to prevent the coagulation of both human and animal blood in plasma and blood fractionation. Calcium and ferric ammonium citrates are used in mineral supplements. 

Metal ions are particularly toxic in a complex with organic molecules, because the latter increase their lipid solubility so that they readily cross the plasma membrane to enter cells. They also cross the blood-brain barrier so that they very effectively gain access to nerve cells in the brain. 

The table also lists important globulins in blood plasma, with their mass and function. The a- and p-globulins are involved in the transport of lipids (lipoproteins see p. 278), hormones, vitamins, and metal ions. In addition, they provide coagulation factors, protease inhibitors, and the proteins of the complement system (see p. 298). Soluble antibodies (immunoglobulins see p. 300) make up the y-globulin fraction. 

The tetracyclines Form an important group of antibiotics. The activity appears to result from their ability to chelate metal ions since the extent of antibacterial activity parallels the ability to form stable chelates. The metal in question appears to be magnesium or calcium since the addition of large amounts of magnesium can inhibit the antibiotic effects. In addition, it is known that in blood plasma the tetracyclines exist as calcium and magnesium complexes.,JS... 

PLASMA. The portion of the blood remaining after removal of the white and red cells and the platelets it differs from serum in that it contains fibrinogen, which induces clotting by conversion into fibrin by activity of the enzyme thrombin. Plasma is made up of more than 40 proteins and also contains acids, lipids, and metal ions. It is an amber, opalescent solution in which the proteins are in colloidal suspension and the solutes (electrolytes and nonelectrolytes) are either emulsified or in true solution. The proteins can be separated from each other and from the other solutes by nltrafiltration, nltracentrifugation, electrophoresis, and immuno-chemical techniques. See also Blood. 

Citrate Since it occurs to the extent of about 0.1 nM in the blood plasma, citrate becomes the pre-eminent small molecule plasma binder of a metal ion like Al3+ that prefers oxygen donor ligands. Citrate complexion of Al3+ in the upper gastrointestinal tract with a pH of 2 to 5, may form a zero-charged complex that may pass through membranes. Sodium citrate as well as calcium citrate may cause a 100-fold enhancement of gastrointestinal Al absorption. The adsorption of Al from Al(OH)3-based antacid rises substantially upon intake of citrate, and therefore these antacids should not be taken with citrus fruit or juices [190]. 

The alkali metal ions are very important for the proper functioning of biological systems, such as nerves and muscles Na+ and K+ ions are present in all body cells and fluids. In human blood plasma the concentrations are... 

May P. M., Linder P. W., and Williams D. R. (1977) Computer simulation of metal-ion equilibria in biofluids models for the low-molecular-weight complex distribution of calciu-m(II), magnesium(II), manganese(II), iron(III), copper(II), zinc(II), and lead(II) ions in human blood plasma. J. Chem. Soc. Dalton Trans. 588—595. 

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