Quantitation of contact-feeding between somatic cells in culture

In search for genetic variation among strains of human fibroblasts, we have developed a quantitative assay for contact-feeding between HGPRT⁺ and HGPRT^- cells. The assay, based on the recovery of 6-thioguanine-resistant clones from mixtures of these cells, reflects the transfer of 6-thioguanylic acid from wild-type to mutant cells. Results indicate that contact-feeding is cell density dependent and a stable characteristic of adult human fibroblasts. No differences in the degree of contact-feeding were noted among 9 strains of Lesch-Nyhan fibroblast recipients, while skin fibroblasts from 17 adults and 9 children, either normal or with various genetic diseases, did not differ in their ability to act as donors. Using the contact-feeding assay as a potential indicator of mutations involving membrane functions, we noted no differences when fibroblasts from a child with Menkes syndrome and two children with cystic fibrosis were used as donor cells. However, when the human donor cell was of fetal origin, a small, but significant decrease in contact-feeding was noted. When this assay was carried out in the presence of cytochalasin B (0.5-0.7 μg/ml), a small decrease in contact-feeding resulted. The same effect also was observed in autoradiographs of cells exposed simultaneously to cytochalasin B (2 μg/ml) and ³H-hypoxanthine. The results of our studies of contact-feeding between Chinese hamster ovary cells and human fibroblasts are compatible with the hypothesis that gap junctions are the ultrastructural basis for this kind of intercellular communication between cells in vitro [1] and suggest that the extent of communication may be determined by the cell which forms the least number of gap junctions.