The significance of ionic concentrations in the internal media of animals

Burton, R. F. (1973) The significance of ionic concentrations in the internal media of animals. Biological Reviews, 48(2), pp. 195-231. (doi:10.1111/j.1469-185X.1973.tb00980.x) (PMID:4592990)

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1. The electrical and ionic gradients across a cell membrane depend on its permeability properties, on the concentration and net valency of the organic constituents of the cytoplasm and on the critical energy barrier to the extrusion of sodium. Such considerations do not, however, explain the small extent to which the concentration of potassium varies in myoplasm which may, instead, be related to the effects of potassium on particular enzymes. 2. The fact that the apparent optimum level of potassium cannot usually be maintained in animals in which the extracellular level of sodium is below about 140 mM may explain why so many non-marine animals have internal media of about that concentration, for more concentrated body fluids would require more work for their regulation. 3. In axoplasm, the concentration of potassium is more nearly proportional to the concentration of sodium in the internal medium and this may partly explain the general correlation between the extracellular levels of sodium and potassium. 4. The relation between pH and temperature in poikilothermic vertebrates is such as to suggest that the prime function of acid-base regulation is to control the ionization of imidazole groups. 5. High tensions of carbon dioxide cannot be maintained in water-breathing animals because of the high solubility of this gas in water as compared with oxygen. Bicarbonate levels are correspondingly low to give a suitable pH. Higher tensions are possible in air-breathing animals, and also necessary if water and heat are to be conserved, but an uncertain upper limit is set by the need for oxygen. The associated higher levels of bicarbonate confer the advantage of better buffering. 6. Calcium and bicarbonate levels are not obviously limited by the solubility of calcium carbonate and a more general limitation on the composition of body fluids seems to arise from the low solubilities of calcium phosphates. 7. The pattern of ionic balance in vertebrate plasma, reflected in a nearly constant value to the molar ratio ([Ca] + 5 × 10--4)/([K] +0.034 [Na]), may be explained in terms of the maintenance of a constant electrical gradient across certain areas of cell membrane, between the inner and outer double layers. 8. The patterns of cation balance in the haemolymphs of molluscs, crustacea and insects are also reviewed, with emphasis on the correlations existing between the concentrations of different cations. An attempt is made to relate the correlations in the mollusca to the concentrations of cations at the surfaces of cells.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Burton, Dr Richard
Authors: Burton, R. F.
College/School:College of Medical Veterinary and Life Sciences > School of Life Sciences
Journal Name:Biological Reviews
ISSN (Online):1469-185X

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