A possible reason for the phalloidin tolerance of hepatoma cells.

In contrast to normal liver cells, AS-30D hepatoma cells are insensitive to phalloidin. The lack of the typical phalloidin response in the latter cells is not due to a deficiency of contractile proteins. Actin prepared from hepatoma cells is able to form filamentous structures and is stabilized in a manner similar to muscle actin. Isolated liver cells were exposed to a medium containing phalloidin and removed after 20 min by centrifugation. The supernatant was incubated again with fresh cells. The procedure was repeated four times. The phalloidin response decreased to about 19% of the control because of the uptake of phalloidin during each incubation. When the same procedure was carried out with AS-30D hepatoma cells, and aliquots of the supernatants were tested with hepatocytes no marked decrease of the phalloidin response was seen. This indicates that hepatoma cells do not consume the toxin as do normal liver cells.