Phosphate-Buffered Saline (PBS) is a widely used laboratory solution designed to support cell integrity outside their natural environment. It helps maintain a stable and balanced medium, crucial for various biological procedures. While PBS provides a suitable temporary environment, cells cannot survive indefinitely in it due to its limited composition.
What is PBS?
PBS is an isotonic, water-based salt solution that mimics the osmolarity and ion concentrations found in the human body. This isotonic property prevents cells from swelling or shrinking due to osmotic imbalances, which can cause cell damage. PBS is also non-toxic to most cells, making it a common choice for biological applications.
The solution primarily consists of sodium chloride (NaCl), potassium chloride (KCl), disodium phosphate (Na2HPO4), and monopotassium phosphate (KH2PO4). These phosphate salts act as a buffer system, maintaining a stable physiological pH, typically around 7.2 to 7.4. This pH stability is important for cell viability and proper cellular function.
Factors Affecting Cell Survival
Several factors influence how long cells can remain viable in PBS. Temperature is a significant determinant; lower temperatures, such as 4°C, slow down cellular metabolic processes, extending cell survival.
The specific type of cell also plays a role in its tolerance to PBS. Some robust primary cells may exhibit greater resilience, while more delicate immortalized cell lines might be more sensitive. Cell density within the PBS solution can also affect survival, as higher concentrations of cells may deplete limited resources or accumulate waste products more rapidly.
PBS lacks essential nutrients like glucose, amino acids, and growth factors, necessary for long-term cell survival and metabolism. Contamination by bacteria or fungi can rapidly compromise cell viability in PBS, as these microorganisms can produce harmful byproducts. The initial health of the cells before being placed in PBS is also important, as healthier cells generally exhibit greater short-term resilience.
How Long Do Cells Survive?
The duration cells can survive in PBS varies considerably. At room temperature, most mammalian cells typically survive only a few hours, generally ranging from 1 to 4 hours, before experiencing significant viability loss.
When stored at lower temperatures, such as 4°C, cell survival in PBS can extend significantly. Under these conditions, some robust cell types might remain viable for several hours, potentially up to a day, but rarely beyond 24 to 48 hours without substantial cell death.
Signs of Cell Distress and Death
Recognizing signs of cell distress and death in PBS is important. Healthy cells appear bright and refractile. As cells experience distress, they might display cytoplasmic blebbing, small, bubble-like protrusions on the cell surface. Other signs include vacuolation, where fluid-filled sacs form within the cytoplasm, or changes in cell shape.
When cells die, they often appear dark, granular, or may undergo lysis, bursting open and releasing their contents. For adherent cells, loss of attachment to the substrate indicates declining health or death. The trypan blue exclusion test is a common laboratory method to assess cell viability; live cells with intact membranes exclude the dye, while dead cells with compromised membranes absorb it and stain blue.