Sodium in biological systems

See also Acid-Base Regulation (Blood) Blood and Potassium and Sodium (In Biological Systems). 

POTASSIUM AND SODIUM (In Biological Systems). Potassium and sodium play major roles in biological processes. Because of the numerous parallels between these two elements in metabolism, they are treated in a single entry, with appropriate distinctions made. 

Sodium in Biological Systems. Sodium is essential to higher animals which regulate the composition of their body fluids and to some marine organisms. The several important roles played by the sodium cation in biological systems, frequently in concert, with the potassium cation are described in file entry oil Potassium and Sodium (In Biological Systems). 

It is interesting to note that the main cation present in ICF is the potassium ion, whereas the principal cation in ECF is the sodium ion. The role of potassium and sodium ions in the biological system is described in the entry on Potassium and Sodium (In Biological Systems). 

The role of sodium in biological systems is quite important, thla has been the main reason for the extensive investigations of sodium NMR in the last decade. A comprehensive review on the subject was recently pidillshed (1). Ue would like to emphasize here that the main reason for the determination of sodium NMR in the systems studied was its biological Importanca and not the vast information one can derive from the amasurement. The chemical shifts of sodium are very small so that information can be deduced mainly from relaxation times (Tj and T2) line intensity and quadrupola coupling constants or splittings. 

Human subjects suffering from myasthenia gravis have received daily doses of 25 mg. for 3 months with beneficial results and no toxic symptoms. Under neutral conditions it is estimated2 that the half-life in water is some 100 years. Hydrolysis is catalysed by acids with fission of a N—P link and the half-life in normal acid is 200 min. Hydrolysis is catalysed by alkali with fission of the POP link the half-life in n sodium hydroxide is 70 days. At biological pH it would appear that it should be indefinitely stable, but as we shall see, other factors besides pH must be taken into account in biological systems. 

An electrochemical system, important particularly in biological systems, is one in which the species are ions and the system is separated into two parts by a rigid membrane that is permeable to some but not all of the species. We are interested in the conditions attained at equilibrium, the Donnan equilibrium. Two cases, one in which the membrane is not permeable to the solvent (nonosmotic equilibrium) and the other in which the membrane is permeable to the solvent (osmotic equilibrium), are considered. The system is at constant temperature and, for the purposes of discussion, we take sodium chloride, some salt NaR, and water as the components. The membrane is assumed to be permeable to the sodium and chloride ions, but not to the R-ions. We designate the quantities pertinent to the solution on one side of the membrane by primes and those pertinent to the solution on the other side by double primes. 

Yelinova et al. reported the oxidation of iV-[2-hydroximino-2-methyl-l-(2-pyridyl)propyl-2]hydroxylamine 239 using sodium hypobromide, generated from bromine and sodium hydroxide in cold condition (0°C), to furnish 3-bromo-3,4-dihydro-4,4-dimethyl-3-(2-pyridyl)-l,2-diazet-l,2-dioxide 240 in 26% yield (Equation 30) <2003MI395>. These oxides were evaluated for their NO donor activities in biological systems. During the last decade, not many new syntheses of diazetidines have been reported. 

The enzymes called ATP phosphohydrolase are widely distributed in the evolutionary chain and in biological systems. In some cases the ATPase is activated either by magnesium (Mg2+ ATPase) or by calcium (Ca2+ ATPase), and in other cases by both calcium and magnesium (Ca2+ Mg2+ ATPase). Another class of ATPase is stimulated by sodium and potassium and is inhibited by ouabain being denominated Na+ K+ ATPase. There are some ATPases that hydrolyze other nucleotides than ATP, however, with a high preference for ATP. 

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