Cell viability during log phase is approximately:
Exponential log phase represents period of maximal health for mammalian cultures. Under optimal conditions of adequate nutrients, pH maintained at 7.2-7.4 by CO2-bicarbonate buffering, temperature 37°C, and absence of waste accumulation, trypan blue exclusion tests reveal membrane intact viable cells at 90-100% because apoptotic signaling minimal, caspase-3 inactive, mitochondrial membrane potential high as indicated by JC-1 aggregation. Mitochondrial succinate dehydrogenase activity robust leading to efficient reduction of tetrazolium salts in MTT assay. Cells display high cloning efficiency and low spontaneous differentiation. In contrast, lag phase viability slightly lower due to trypsin-induced injury, plateau phase shows gradual decline as contact inhibition triggers quiescence and modest increase in annexin V positivity, and death phase viability drops below 50% with extensive debris. Accurate viability assessment during log phase is crucial before seeding plates for experiments, performing transfections requiring high viability, and virus production where defective particles increase from dying cells. Regular monitoring ensures high-quality inoculum and reproducible experimental outcomes.
Ref: Freshney Ch.18 Viability during log 90-100%; ATCC Cell Viability trypan blue exclusion exponential phase near maximal.