Volume Regulation in Carp Kidney Tissue as Influenced by Various Osmotic Agents

To what extent does the sodium pump (the plasma membrane Na,K-ATPase)contribute to volume regulation of animal cells? According to the original concept of Wilson (1954) and Leaf (1956) the sodium pump solves entirely the problem of volume maintenance in isotonic media, since “effectively impermeant” sodium ions (continually extruded by the pump) compensate for the Donnan excess of osmotic pressure, resulting mostly from the high concentration of diffusible counterions of macromolecules in the cytoplasm.