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.
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability / Q000187:drug effects*; D004175:Diptera / Q000033:anatomy & histology; D004594:Electrophysiology / Q000295:instrumentation; D007478:Iontophoresis; D008274:Magnesium / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D008962:Models, Theoretical; D012469:Salivary Glands
D008274:Magnesium; D002118:Calcium