LIMITED DIVISION OF LOW-DENSITY ADULT-RAT TYPE-II PNEUMOCYTES IN SERUM-FREE CULTURE

A previously reported serum-free medium for the culture of adult rat type II pneumocytes has been further defined by the addition of 10 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer and 700 U/ml catalase. Both additions significantly enhanced [H-3]thymidine incorporation into pneumocyte DNA between days 5 and 6 of culture. In the presence of 100-mu-g/ml bovine pituitary extract, both insulin-like growth factor (IGF) I (20 ng/ml) and II (25 ng/ml) further increased [H-3]thymidine incorporation into pneumocyte DNA over that observed with the basal medium. When type II pneumocytes were plated at 2.75 x 10(5) cells/cm2 there was a plating efficiency of 50 +/- 5%, and the increased DNA synthesis in response to IGFs was not associated with an increase in cell number. When the plating number was reduced to 1.6 x 10(5) cells/cm2 the plating efficiency was only 23 +/- 2%. At this low cell density a doubling of cell number was observed in response to IGF-I between days 4 and 9 of culture.