Slide 1-4 : Mechanisms of Intercellular Communication
Direct Communication :
o Gap Junctions: When two cells are in close proximity, but because of opposite
charges, cannot touch, protein structures can connect the two. Called a connexon.
Important in growth and differentiation. The down regulation in cancer cells implies
that because there is no communication, resulting in uncontrolable cell division.
Intercalated disks are found in cardiac. Pore size is very small, permits the passage
of sugars, amino acids and ions.
o Nanotubes: Nanotubes are formed from the plasma membrane. They are longer
than gap junctions, and have a larger pore diameter. Involved in transfer of nucleic
acids, even small organelles, between cells. May be involved in the transfer of
pathogens or virus (such as HIV) and prions (“mad cow disease”). Prions are
misfolded proteins that are infectious. They act by serving as a template for native,
properly folded proteins, thereby converting them into a misfolded state. Diseases
usually work by hijacking the cells, this is usually done through the nanotube. Mad
cow disease targets the central nervous system
o Mechanosignals: Mechanosignalling can occur in a few ways:
1. A filamentous network between cells acts as a sensor. It can be bent by cells,
particles or fluid moving past; filaments can also be tugged by the movement of attached
2. Direct physical stress to the cells, as commonly occurs on vascular endothelial
cells and the underlying smooth muscle. This involves “cyclical” strain due to the pulsatile
nature of blood flow in arteries/arterioles; shear stress of blood flow, and the hydrostatic
pressure exerted back by the cell wall. Thought to be a mediator in vascular inflammation
and progression of atherosclerosis. Excess pressure leads to cardiac issues.
Slide 5 - 7 : Indirect Communication : Chemical Messengers
a) A cell releases it’s hormone, and a receptor on another cell
Examples of paracrine signaling:
• clotting factors, growth factor
• Secreted proteins and hormones can act in a paracrine