Gap and low-resistance junctions between cells in culture.

In vitro cultured cells are connected by different membrane junctions which may serve as a matrix for the monolayer, but which may also enable intercellu­ lar communication. Some of these intercellular infor­ mation exchanges may be detected by ionic coupling between the cells through so-called “low-resistance junctions” . Gilula and cow orkers1, for instance, have shown that metabolic cooperation between inosinic guanylic pyrophosphorylase(IPP)-positive chinese hamster cells and their IPP-negative sublines is only present in ionically coupled fibroblasts, and only between these coupled cells could gap junctions be found. Such gap junctions have also been de­ scribed by other authors 2-5 for different ionically coupled fibroblastoid cell types. Recently evidence has been given 6 for a correlation between the gross morphology of established cell lines and ionic coupling: Fibroblastoid cells are ionically coupled, epithelioid cells are not. We have, therefore, in­ vestigated epithelioid cells as well as fibroblastoid cells of normal and malignant origin in order to test whether epithelioid cells also have gap junctions, or whether the correlation between low-resistance junctions and gap junctions could be confirmed. The freeze-fracture technique was employed preferentially to thin sectioning since it allows the examination of large areas of membrane surface. By this method the coupled fibroblastoid cells (3T3 and BICR/ M1R-K) have been shown to possess gap junctions, whereas, with the same method and with as much as a three times longer investigation period, we could