Osmolysis

Osmolysis, also called osmotic lysis, is the rupture of cells caused by osmotic pressure differences across a semi-permeable membrane. It occurs when cells are placed in a solution with lower osmolarity than their cytoplasm (a hypotonic environment), causing water to diffuse into the cell. If the influx increases the cell’s volume beyond the membrane’s capacity, the cell may burst, releasing its contents.

Cell type and structural features influence osmolysis. Animal cells and many bacteria are susceptible to lysis in hypotonic solutions because they lack rigid cell walls; plant and fungal cells with intact cell walls are more resistant, though extreme osmotic shifts can damage them as well. Hypertonic environments cause the opposite effect, water efflux, leading to cell shrinkage (crenation in some cells) and, in plants, plasmolysis.

In laboratory settings, osmotic lysis is used to disrupt cells to release intracellular components, such as nucleic acids or proteins. It is often achieved by exposure to distilled water or hypoosmotic buffers, sometimes in combination with detergents or mechanical disruption. Osmotic lysis is also employed to selectively remove red blood cells from blood samples or as a first step in cell fractionation protocols.

Limitations include incomplete lysis of cells with strong cell walls, potential premature release of degrading enzymes, and the need to control osmolarity to avoid unintended damage to target molecules. For complete disruption, osmotic lysis is commonly paired with other methods such as sonication, enzymatic digestion, or detergent-based lysis.