The contribution of cell death to medium-released fractions of cell cultures.

Cell death was estimated by prelabeling primary chick embryo skeletal muscle cell cultures with [3H]thymidine and by subsequently measuring the release of label into complete culture medium or serum- and embryo-extract-free medium for a 6 h period. Cultures of the established muscle cell line L6 and the fibroblastic cell line 3T3 were used for comparative purposes. Comparison of the nigrosin exclusion test with the thymidine release test shows that the former underestimates cell death because it measures only the instantaneously occurring cell death. The [3H]thymidine release test estimates the cumulative amount of cell death. From cumulative cell death estimates it is calculated that 12.0 and 17.8% of the 3H-fucosylated medium-released fractions from primary cell cultures are the result of cell death contamination when release occurs in complete or macromolecule-free media, respectively. High speed centrifugation is shown to eliminate most contamination from cell death. Evidence is presented that the absence of macromolecules in the culture medium has little effect on the release process. Contamination of the released fraction resulting from cell death is much less in the established cell lines than in the primary cells. It is concluded that the release process can be studied in primary muscle cell cultures and especially in established cell lines if adequate precautions are taken and if corrections for cell death contamination are taken into account.