Junctional membrane uncoupling. Permeability transformations at a cell membrane junction

Area of Science:

• Cell Biology
• Membrane Physiology
• Ion Transport

Background:

• Junctional membranes facilitate cell-to-cell communication.
• The role of divalent cations in junctional membrane permeability is not fully understood.

Purpose of the Study:

• To investigate the influence of calcium (Ca++) and magnesium (Mg++) on junctional membrane permeability in Chironomus salivary glands.
• To elucidate the mechanisms by which these ions alter membrane conductance and their roles in cell coupling.

Main Methods:

• Iontophoresis of Ca++ into cells.
• Induction of cell surface membrane leaks.
• Experimental manipulation of perijunctional insulation using trypsin, anisotonicity, alkalinity, and chelation.

Main Results:

• Elevated Ca++ and Mg++ concentrations significantly reduce junctional membrane permeability (1-3 orders of magnitude).
• This permeability decrease approaches that of nonjunctional membranes.
• Three distinct mechanisms were identified for achieving this permeability transformation.

Conclusions:

• Ca++ and Mg++ are critical regulators of junctional membrane permeability.
• These ions play multiple roles in junctional coupling, including regulating junctional membrane permeability, perijunctional insulation, and mechanical stability.
• The regulation of junctional membrane permeability by Ca++ and Mg++ is independent of their roles in perijunctional insulation and mechanical stability.