Communicating Junctions - Gap Junctions

Gap junctions and plasmodesmata are specialized sites of communication between adjoining cells in animals and plants respectively.

Gap Junctions

Gap junctions readily allow the passage of small molecules and ions required for rapid communication (such as heart tissue), but do not allow the passage of larger molecules such as proteins

Gap Junction

• Junctions that provide direct connections between cells
• Allows passage of small molecules from cell to cell in a tissue
• Channels or pores through the membranes of two cells and across the intercellular space.
• Form electrical synapses
• Direct transmission of action potential without transmitter, receptors etc
• Integrate the metabolism of the cells
• Metabolic coupling or metabolic cooperation transfer of molecules that the neighbouring cell cannot synthesize (second messengers, precursors of DNA and RNA)
  
  
  Molecular Structure of Gap junction

  

  Connexon

  • A ring of six transmembrane proteins called connexon proteins creating a pore that connects cells
  • Two connexons on neighbouring membranes form a transmembrane channel that interconnects the cytoplasm of two cells
  • Connexons are size filters
  Regulation of Gap junctions
  • Flip between open and closed states as other channels do
  • Cells may modulate the degrees of coupling
  • Cytoplasmic levels of Ca2+ and pH
  • Phosphorylation
  • Oleamide-close gap junctions and induces sleep
  Example-Excitable tissue such as heart and muscle