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Donnan effect on chloride ion distribution as a determinant of body fluid composition that allows action potentials to spread via fast sodium channels

DOI: 10.1186/1742-4682-8-16

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In many excitable cells, the spreading of action potentials is mediated through fast, voltage-gated sodium channels. Tissue cells share similar concentrations of cytoplasmic proteins and almost the same exposure to the interstitial fluid (IF) chloride concentration. The consequence is that similar intra- and extra-cellular chloride concentrations make these cells share the same Nernst value for Cl-.Further extrapolation indicates that cells with the same chloride Nernst value and high chloride permeability should have similar resting membrane potentials, more negative than -80 mV. Fast sodium channels require potassium levels >20 times higher inside the cell than around it, while the concentration of Cl- ions needs to be >20 times higher outside the cell.When osmotic forces, electroneutrality and other ions are all taken into account, the overall osmolarity needs to be near 280 to 300 mosm/L to reach the required resting potential in excitable cells. High plasma protein concentrations keep the IF chloride concentration stable, which is important in keeping the resting membrane potential similar in all chloride-permeable cells. Probable consequences of this concept for neuron excitability, erythrocyte membrane permeability and several features of circulation design are briefly discussed.This theoretical paper seeks to interpret similarities in pH, electrolyte and protein compositions of body fluids among diverse animals as requirements imposed by their excitable tissues, particularly neurons and muscle cells.The logic that follows is based on a previously published argument that similar body fluid osmolarity in various animals is dictated by the opposed Donnan effects of cell proteins and of sodium ions sequestered in the extracellular fluid (ECF) [1]. The conclusion of the cited paper is that the ubiquitous ECF Na+ concentration is determined by the average osmotic burden on animal tissue cells.The presence of proteins in any solution exerts two effects on the traff


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