Composition of the Intracellular Fluid

In contrast to the extracellular fluid, where sodium predominates, the quantitatively dominant intracellular cation is potassium (K+). The sodium concentration inside the cell is about 10 times smaller than that outside it. The major portion of the intracellular anions consists of proteins, while phosphates (HPO4
−/H2PO4 −) are present in lower concentrations.