Cytolysis is a cell death which occurs as the result of a rupture in the cell's membrane. When a cell experiences cytolysis, it bursts, scattering its contents in the process. A number of things can cause cytolysis. This process is very different from apoptosis, or programmed cell death, in which a cell gradually shuts itself down, or is triggered to do so by another cell. The cytotoxic (or “toxic to cells”) cells in the immune system often utilize apoptosis to neutralize infected cells.
A common reason for cytolysis to occur is an interruption in the osmotic balance. Normally, bodily fluids make up an isotonic solution, meaning that their balance of salts is similar to the cells, and cells experience no net loss or gain as water and salts flow through them. This allows cells to stay healthy, and it provides a way for them to be flushed to remove toxins and refreshed with necessary minerals and other compounds.
If the body fluid becomes hypotonic, meaning that it is a solution of lower concentration than that found in the cell, the cell will tend to gain water. This is the result of osmotic pressure, which encourages solutions to flow from areas of low concentration to areas of high concentration. If the cell gains enough water, it can rupture, experiencing cytolysis and dying. This can happen to people experiencing water intoxication, as their body fluids become dangerously dilute, causing the cells in their bodies to swell.
Researchers can induce cytolysis in the laboratory setting by putting cells into a hypotonic solution which will cause them to swell and eventually burst. This can be used to prepare cells and solutions for various experiments and procedures, and to explore the boundaries of cytolysis to learn more about how specific types of cells work.
Some viruses can also initiate cytolysis by damaging the cell membrane. Viruses use this to their advantage, first colonizing a cell and forcing it to reproduce their DNA, and then causing the cell to rupture so that copies of the virus are scattered, allowing the virus to spread. By contrast, when an infected cell is attacked by the immune system, the immune system kills the cell without rupturing the cell membrane, ensuring that the virus cannot spread.
Some cells and organisms have measures in place which are designed to prevent rupture of the cell membrane. Plants, for example, have very rigid cell walls which resist bursting, although if a plant is frozen, the water in its cells can rupture the cell wall.