33 



ware (Corniny). Transfer of cell stocks and experimental 

 procedures were performed in a laminar flow hood isolated 

 from other laboratory activities. 



Human amnionic cells, AV3 , were obtained from Dr. 

 G. Gifford, Department of Immunology and Medical Microbiology, 

 University of Florida, Gainesville, Florida. AV3 cells 

 were grown in Eagles MEM with Earle 's balanced salts, 10% 

 heat inactivated FCS (56°C, 30 minutes) and penicillin- 

 streptomycin. They were routinely passaged every two days 



4 2 



at a density of 1.25 x 10 cells/cm . For transfer of 



cells, the cell monolayer (approximately 80% confluent) 



was rinsed two times with 0.15M PBS containing 0.05mM EDTA. 



One milliliter of PBS containing 0.02% trypsin and 0.05M 



EDTA ( trypsin-EDTA) was added and the cells were allowed 



to detach from the culture vessel, generally within one 



to two minutes. Four milliliters of fresh 37°C media was 



added and cell counts were made with a hemocytometer . 



Cells were transferred to new flasks with fresh media after 



dilution and incubated. 



Chinese Hamster Ovary cells, CHO, were obtained from 



Dr. K. D. Noonan , Department of Biochemistry, University of 



Florida, Gainesville, Florida. Three CHO lines were used, 



M-7, II-7 and H-7Wcr. M-7 and H-7 differ primarily in their 



response to dibutryl cyclic adenosine monophosphate (db-cAMP) 



whereas H-7Wcr is a Con A resistant line derived from H-7. 



CHO cells were maintained in McCoy's 5A (modified) medium 



with 10% FCS, penicillin and streptomycin. They were 



