The transfer of purine metabolites via the medium rather than through cell contacts

When the medium in which mouse B82 cells had been grown for 24 h with ³H]hypoxanthine was given to HGPRT⁻ Chinese hamster cells (CHW-1102), the acid-insoluble fraction of these cells became radioactive. When the medium in which mouse B82 cells had been grown for 24 h without ³H]hypoxanthine was given to CHW-1102 cells at the same time as ³H]hypoxanthine was added, the acid-insoluble fraction of the cells did not become radioactive. This indicates that CHW-1102 cells acquire from the B82 medium ³H material and not the ability to utilize hypoxanthine. Very little radioactivity was found in the acid-insoluble fraction of the B82 medium and when the medium was given to CHW-1102 cytoplasms, they did not become labelled. These results suggest that ³H purine metabolites (and not ³H nucleic acids) are responsible for the radioactivity in the CHW-1102 cells. Such ³H metabolites were also present in the medium of mouse L929 cells, but were absent in the medium of Chinese hamster (V79), mouse (A9), Syrian baby hamster kidney (BHK) and human fibroblasts. The cells were judged to be free of mycoplasma by three different criteria. This exchange of metabolites through the medium is referred to as contact-independent metabolite transfer (CIMT).