Permeabilization of hepatocytes by a saponin and the effects of dextran

The process by which a saponin derived from Gypsophila plants permeabilizes rat hepatocytes was studied. When monolayer cultures were incubated with 25 micrograms/ml saponin in phosphate buffered saline, the amount of cell-bound saponin increased for at least 90 min. Release of intracellular K+ started immediately, with a t1/2 of about 5 min. ATP and lactate dehydrogenase (LDH) began to appear in the medium only after lag periods of 10 to 20 min with t1/2s of 20 to 30 min. Removing the saponin from the medium after 15 min stopped any further release of ATP and LDH, showing that increased permeability to small ions alone does not lead to lysis by colloid osmotic pressure. However, the lysis that occurred upon 30 min continuous incubation with the saponin could be inhibited (delayed) by the addition of an osmotically active compound - a dextran. These results indicate that increasing binding of the saponin destabilizes the plasma membrane so that it will rupture from the colloid osmotic pressure.