Selectivity in metabolic cooperation between cultured mammalian cells

Selective communication between cultured mammalian cells was detected as selectivity in metabolic cooperation. Whilst the majority of the cell types examined (human skin fibroblast, PC13, G3, Don, PyY) showed metabolic cooperation at almost all (>95%) of their homotypic cell-to-cell contacts, they did not necessarily show cooperation at such a high proportion of their heterotypic contacts. Less than 10% of G3/human fibroblast contacts, and usually less than 30% of G3/PC13 contacts were observed to be positive for metabolic cooperation. L cells differed from these other cell types in that they formed permeable junctions at a greater proportion of their heterotypic cell-to-cell contacts (contacts between L and PyY cells) than their homotypic contacts. We question why it was that the contacts between any two poorly-compatible cell types were positive for metabolic cooperation in only a small proportion of cases. We could find no indication that this phenomenon was attributable to heterogeneity within the cell stocks. Time course studies upon PC13 and G3 cells showed that the proportion of cooperation-positive contacts was not constant but that it continued to increase over many hours of co-culture. In comparing the homotypic and heterotypic interactions of these cell types, selectivity manifested as a difference in the rate of appearance of permeable junctions. We discuss possible explanations for these findings.