Functionally polarized layers formed by epidermal cells on a permeable transparent collagen film.

Rat epidermal cells were cultured on a transparent collagen film, which was permeable to low Mr substances. Then the cells were bathed in both media (apical and basal), which were separated by the collagen membrane. The cells formed a multi-layered epidermal sheet with well-developed structures of desmosomes. This sheet on a permeable support was found to be an effective permeability barrier for glucose and amino acids. The epidermal layer showed functional polarity for the uptake and excretion of nutrients, metabolites and newly synthesized proteins: glucose and amino acids were taken up exclusively from the basal medium and lactate was secreted selectively into the same medium, whereas ammonia was secreted into the apical medium. The apical media became more acidic than the basal ones, presumably due to the preferential distribution of H+ transport systems on the apical side of the epidermal layer. The epidermal cells that expressed functional polarities in vitro as described above were able to proliferate and differentiate, and remained healthy for as long as at least 40 days even using a conventional culture medium with foetal calf serum, but without any special growth factors and feeder cells.