Role Played by GAP Junctions in Cell-Cell Communication

Abstract

Intercellular communication is a necessary prerequisite for the evolution of complex multicellular organisms. Without information exchange neither plants nor animals would have developed. The different possibilities of intercellular communication can be classified as three independent signal pathways: 1.) indirect signal transfer by secreted molecules, 2.) direct signal transfer by plasma membrane bound molecules (receptors) and 3.) direct signal transfer from cell to cell by channels which span the plasma membranes of adjacent cells. Whereas in the first two cases the signal flow is unidirectional (hormone, neurotransmitter; sperm-egg-binding, immune system), in the latter case no rectification is observed. These cell to cell channels — called gap junctions — not only allow an intercellular pathway for the transfer of information between cells but also connect adjacent cells mechanically. They must, therefore, well be discriminated from desmosomes which anchor cells together to form structural or functional units as well as from tight junctions which seal membranes of epithelial cells to each other so that the paracellular path becomes impermeable to molecules and a polarity of apical and basolateral surface is maintained.