Studies on the formation of a permeable cell membrane junction

Summary

Individual cells (macroblastomeres) of newt embryo were brought into contact, and electrical coupling was monitored during the formation of permeable membrane junction. In one set of experiments, the cells were allowed to establish contact at random membrane spots by spontaneously moving cell processes. Coupling became detectable 8–14 min after contact. In another set, contact was imposed, by micromanipulation, at membrane spots of known junctional history. The basic experiment was (i) to make a junction (conditioning junction) at randomly chosen membrane spots, (ii) to pull the cells apart interrupting their electrical coupling (uncoupling), and (iii) to make a new junction (test junction) either at the same spots that contained the conditioning junction or at different ones. The times required for coupling onset at test junctions fell into two classes, depending on whether in the uncoupling step the membrane continuity between the two cells had been broken or preserved. When all membrane continuity had been broken, coupling through the test junctions became detectable within 4–20 min after membrane contact. This was so when the spots of membrane contact contained conditioning junction as well as when they did not. When membrane continuity (but not coupling) had been preserved in the form of submicroscopic strands, coupling through the test junction set in within 1 sec of joining the cells at spots containing conditioning junction. This capacity for rapid coupling persisted for roughly 10 min following the uncoupling step; thereafter the time of coupling onset was of the class with broken membrane continuity. During development of junction, the coupling coefficients rose gradually over 10–30 min from the detectable level (0.03 or 0.05) to a plateau (0.3–0.9). The cells were capable of developing and of maintaining coupling throughout their entire 100-min division cycle. Treatments with colchicine (0.2–1.1mm) and with cytochalasin B (0.5–1 μm), blocking cytokinesis and division, did not prevent the development or maintenance of coupling. Treatment with dinitrophenol (1mm) prevented the development of coupling, but not that of cell adhesion, and (3mm) blocked reversibly the coupling in established junction.