Cell-to-cell communication in monolayers of epithelioid cells (MDCK) as a function of the age of the monolayer.

We explore the existence of cell-to-cell communication in monolayers of MDCK cells plated at high densities so that they form a continuous monolayer in a few minutes. Lucifer Yellow CH is injected in the cytoplasm of a given cell by using a glass microelectrode with a fine tip (ca. 100 M omega) and passing square pulses of current of 1.0 nA that last 10 msec, every 20 msec, during 1 to 3 min. We then examine the monolayer with fluorescence microscopy. In 27 out of 111 cells injected during the first 4 to 15 hr after plating, the dye was transferred to neighboring cells. Electron micrographs of freeze-fracture replicas prepared at this time, show that 20 to 25% of the lateral surfaces present the aggregates of intramembrane particles typical of gap junctions. These early hours correspond to the formation of occluding junctions and polarization into an apical and a basolateral domain of the plasma membrane (Cereijido, Meza & Martínez-Palomo, 1981). Cell-to-cell coupling then decreases sharply and, in the period between the 1st and 3rd day (mature monolayers), only 4 out of 49 injected cells were able to transfer the dye to their neighbors in the monolayers. No image of gap junctions was found in freeze-fracture replicas of mature monolayers. The degree of coupling between cells, as well as the number of cells coupled to the injected one, were highly variable. The lack of coupling between cells in mature monolayers observed in this article with Lucifer Yellow CH and electron microscopy is in keeping with the absence of electrical coupling observed in a previous work (Stefani & Cereijido, 1983). The transient existence of communicating junctions observed in monolayers of MDCK cells is similar to that described in the literature for embryo tissues during development.