The course of culture of human keratinocytes: increase of heat-labile fraction of glucose-6-phosphate dehydrogenase.

Human epidermal keratinocytes in cell culture are unique in reorganizing the formation of a stratified cellular sheet and performing terminal differentiation. The course of keratinocytes in culture was delineated over 50 days in the primary culture. The rapid increase in total DNA content commencing 2 weeks after plating corresponded to the appearance of small polygonal keratinocytes in groups. The DNA content reached its maximum after 25 days of cultivation, decreasing gradually thereafter. The protein content increase slowly until 16 to 18 days of cultivation, and then increased rapidly, though slightly behind the rapid increase in DNA. The maximum value of protein content was reached at 32 days, after which the value decreased when the keratinized cells of the uppermost layer began to detach. The heat-labile fraction of glucose-6-phosphate dehydrogenase was increased in 33- and 43-day cultures, when the DNA content was decreasing.