Junctional Membrane Uncoupling Permeability transformations at a cell membrane junction

The permeability of the membrane surfaces where cells are in contact (junctional membranes) in Chironomus salivary glands depends on Ca ++ and Mg++. When the concentration of these ions at the junctional membranes is raised sufficiently, these normally highly permeable membranes seal off; their permeability falls one to three orders, as they approach the nonjunctional membranes in conductance. This permeability transformation is achieved in three ways: (a) by iontophoresis of Ca ++ into the cell; (b) by entry of Ca ++ and/ or Mg ++ from the extracellular fluid into the cell through leaks in the cell surface membrane (e.g., injury); or (c) by entry of these ions through leaks arising, probably primarily in the perijunctional insulation, due to trypsin digestion, anisotonicity, alkalinity, or chelation. Ca++ and Mg++ appear to have three roles in the junctional coupling processes: (a) in the permeability of the junctional membranes; (b) in the permeability of the perijunctional insulation; and (c) a role long known--in the mechanical stability of the cell junction. The two latter roles may well be closely interdependent, but the first is clearly independent of the others. I N T R O D U C T I O N A wide variety of epithelial tissues are now known in which cells are in close communication. At the junctions of these cells, surface membrane permeability is so modified that many kinds of ions and molecules can move freely from one interior to another (Loewenstein and Kanno, 1964; Loewenstein et al., 1965; Potter et al., 1966; Loewenstein, 1966). This paper deals with the question of the stability of cell communication. The question is obviously linked with that of structural (mechanical) stability of the junctional elements which hold the ceils together, and our first steps in exploring the question were guided by procedures long in use for mechanical dissociation of cells: Ca ++ removal, trypsin digestion, and application of solutions of high p H (Ringer, 1890; Herbst, 1900; Roux and Jones, 1916; Chambers, 1940; Holffreter,