Decreased 3H-uridine incorporation and increased 3H-adenosine incorporation by HeLa cells exposed to autologous culture fluid.

Actively growing HeLa monolayer cultures briefly exposed to the culture fluids (CF) from confluent HeLa cultures and labeled simultaneously or subsequently, incorporated less 3H-uridine (3H-UR) but more 3H-adenosine (3H-AR) than control cultures similarly exposed to fresh medium and labeled. Exposure to CF inhibited the uptake as well as the incorporation of 3H-UR by cultures. The inhibition of 3H-UR incorporation by CF-exposed cultures could be reduced by increasing the concentration of 3H-UR in the labeling medium. Both the inhibition of 3H-UR incorporation and the stimulation of 3H-AR incorporation were prevented by washing the CF-treated cultures with phosphate buffered saline before labeling. Similarly, both effects could be producted in HeLa cultures exposed to fresh medium containing 1 X 10(-5) M uridine instead of to CF. Therefore, the observed effects of CF on label incorporation were probably due to the presence of uridine or a related compound, and the inhibition of 3H-UR incorporation resulted from reduced uptake of 3H-UR rather than from reduced RNA synthesis by exposed cells. The active agent in the CF, formed only when cultures were incubated at physiological temperatures, was not a product of medium decay. It was a cellular product formed equally well by cultures incubated in medium containing dialysed or whole serum.