When liver slices immediately after their removal from the body are immersed in graded solutions of sodium chloride, movement of water does not follow a course determined by movement of sodium ions. From hypotonic solutions sodium enters slowly and swelling proceeds rapidly but with increasing concentration entrance of sodium increases and swelling diminishes in accord with the osmotic relations between tissue and the medium.
The extracellular fluid of liver has the same osmotic pressure as blood plasma, and entrance of water into liver slices from media with greater molar concentration is determined by the intracellular pressure of the parenchymatous cells of the tissue.
The plasma membrane of the liver cell is semipermeable to electrolytes but its semipermeability is imperfect, may be impaired, and when in media isotonic with the cells some of the electrolyte enters them. With continued entrance permeability to both electrolyte and water increases and in case of sodium become evident after 15 or 20 minutes.
A medium more favorable to the tissue prolongs the period of isotonicity. In solutions with electrolytes otherwise similar to those of the blood plasma, e.g. Krebs-Ringer solution, but with molar concentration of electrolytes approximately doubled by addition of sodium chloride isotonicity may be prolonged during a period of 1 hour or more.
When potassium chloride is added to the Krebs-Ringer solution so that its potassium content has been increased 10-fold the water intake of liver cells has not varied in accord with the potassium content of the medium.
In a medium with the electrolyte contents of blood plasma (Krebs-Ringer solution) liver cells after 1 hour gain sodium and lose potassium, but later potassium maintains a nearly constant level though swelling increases.
Less sodium enters and less potassium is lost from liver cells at 0°C. than at 38° and 0°C. swelling is greater.
Movement of water between cells and extracellular fluid may occur independently of changes in the sodium or of potassium content of cells and doubtless is in part determined by substances associated with metabolism.