Communication compartments in mixed cell cultures.

Mixed cultures of epithelial (BRL) cells and fibroblasts (BHK), which sort themselves out into separate domains of each cell type, form communication compartments. Electrical coupling, dye coupling and metabolic coupling measurements have been used to show that small ions and molecules can move freely via intercellular junctions between all the cells in a domain, while their movement across the boundaries between domains is severely restricted. Metabolic coupling is the most sensitive method for detecting trans-boundary communication but the results obtained from all three methods are compatible. The data suggest the reduced transfer across the boundaries is due to fewer channels, resulting from a lower frequency of junction formation between heterologous cells, rather than to channels of smaller diameter. Concentration gradients of small cytoplasmic molecules can be established within these communication compartments which are similar to those predicted to explain pattern formation in developing systems. It is suggested that the cell surface features which cause this sorting out are also responsible for the reduced frequency of heterologous junction formation and hence for compartmentalization.