Putrescine Uptake by Alveolar Epithelial Cell Monolayers Exhibiting Differing Transepithelial Electrical Resistances

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Abstract
Rat alveolar type II cells were isolated following elastase digestion and cultured on polycarbonate filters at various densities and in different media. Two days after seeding, the cells formed a monolayer on the filters which consisted predominantly of type II cells, these then de-differentiated to a alveolar type I-like cell monolayer by day 6. The seeding density and media utilized affected the transepithelial electrical resistance (TEER) generated by the monolayer. Only certain culture conditions allowed the production of a monolayer that mimics, putatively, the in vivo alveolar epithelium (TEER greater than 1000 omega cm2). Vmax and K(m) values for the uptake of putrescine by monolayers exhibiting low and high TEERs on day 6 were determined. The capacity of the putrescine uptake mechanisms was greater in cell monolayers exhibiting a high TEER than those exhibiting a low TEER, suggesting that the TEER does not only measure the "tightness" of the monolayer but contains an element representative of the viability of the cell monolayer. The selection of appropriate TEERs for cell culture investigations is discussed.