Re: what role do gap junction play in cellular signalling

Gap junctions are composed of proteins that assemble to form pores in the
membranes of cells called connexons.  A connexon on one cells linked to a
connexon from a neighboring cell to form an open channel between the
cells.  This channel is wide enough to allow the exchange of small
intracellular signalling molecules between cells such as calcium and cyclic
AMP, but not larger macromolecules like proteins or nucleic acids.  In
tissues that contain electrically excitable cells (for example smooth
muscle, cardiac and nerve cells) allow actions potentials to spread rapidly
without having the delay associated with chemical synapses.  In addition it
is known that gap junctions play a role in embryonic development.  When
cells begin to differentiate they start to lose their gap junctions and
only maintain connections with cells of the same tissue type maintaining
the ability to behave as a cooperative assembly.  It is also thought that
gap junctions may play a role in long range signalling.  This would happen
for example when a signalling molecule is in high concentration in one area
within a given tissue, but low in a different area.  This concentration
gradient could provide cells with positional information to control
differentiation of a tissue.