Intoxication of cells from different-aged embryos by diphtheria toxin

Different methods were used to assay diphtheria toxin sensitivity of fibroblast and heart cell cultures from chicken embryos of various ages. As defined by inhibition of protein synthesis, fibroblasts from 18-day and younger embryos respond more rapidly to toxin than fibroblasts from older embryos. The response of heart cells cultures is independent of the age of the embryos and is similar to the response of fibroblasts from 18-day embryos. Since the EF-2 content is 10-fold less in fibroblasts from 21-day-old embryos, the different responses of protein synthesis to intoxication appear to reside at the membrane level. Cytotoxicity assays in cell culture and in vivo toxin sensitivity assays show that cells from both young and old embryos, as well as whole embryos, are equally sensitive to toxin. Thus, short-term (5-h) measurements of inhibition of protein synthesis are insufficient for determining the relative sensitivity of cells to intoxication as defined by cell death.