Measures of viability in isolated cells.

A well-recognized essential requirement of most biological investigations using cellular preparations is the assertion of cell viability. However, there seems to be little agreement on the criteria to be applied in establishing this cellular property. Cell viability has been assessed as morphological integrity and metabolic capacity, or interpreted as a specific cellular function, e.g., phagocytosis. If viability is identified as the ability of the cells to carry out a particular metabolic function, e.g., a biosynthetic reaction, cell integrity is of lesser importance in characterizing these cells. On the other hand, whenever the biological event under investigation is dependent upon an intact plasma membrane, assertion of this condition during the experiment is of primary importance in assuring an unequivocal interpretation of the data. The most widely applied criterion for investigation of cell permeability is the exclusion by cells of dyes with high molecular weights (“vital stains”), e.g., trypan blue or eosin (1,2). In the course of our investigations of mechanisms of cellular drug transport (3-6) and in conjunction with recently developed procedures for the separation of human and rat blood cells (7,8), estimation of viability was carried out considering various criteria. Results of these experiments suggested that trypan blue was a relatively poor and insensitive indicator of the presence of a morphologically intact, nonleaking plasma membrane. In view of these findings and considering the increasing utilization of isolated cells in clinical investigations, it was of interest to reevaluate frequently applied measures of cell viability.