Junctional Membrane Uncoupling

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Abstract
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 1 to 3 orders, as they approach the nonjunctional membranes in conductance. This permeability transformation is achieved in 3 ways: by iontophoresis of Ca++ into the cell; 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 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 3 roles in the junctional coupling processes: in the permeability of the junctional membranes; in the permeability of the perijunctional insulation; and a role long known[long dash]in the mechanical stability of the cell junction. The 2 latter roles may well be closely interdependent, but the 1st is clearly independent of the others.