Accumulation of ganglioside GM1 in a medium conditioned by the culture of rat hepatocytes

We studied the dynamics of accumulation of the ganglioside GM1 in a medium conditioned by the rat hepatocytes cultured in a serum-free medium on collagen-covered slides. GM1 was quantitated using ELISA and cholera toxin B-subunit conjugated with radish peroxidase. After 5 min conditioning of the medium, 24 h cultures of a certain density accumulated GM1 in the medium, whose concentration could correspond to 25% of the content of this ganglioside in the cultured cells. When the exposure time was increased, the rate of GM1 accumulation was sharply reduced. The culture density was established (0.4-0.9 x 10(-3) cells/cm(2)), when every thousand of cells released the highest amount of GM1 in the conditioned medium (about 0.035 pmol/1000 cells). Such cultures (109-295x10(-3) cells) accumulated 60-90 pM GM1 in 30 ml conditioned medium within 5-60 min.