Connexon
Connexon is the assembly of 6 subunits of protein connexin with a hollow center that forms a channel through the plasma membrane at a gap junction[1]. A single gap junction may consist of a few or as many as thousands of clustered connexons. Each connexon has a diameter of about 7 nm and a hollow center that forms a very thin hydrophilic channel through the membrane. The channel is about 3 nm in diameter which only allow small molecules and ions to pass through, while not large enough to provide passage for large molecules such as proteins. When the connexon from adjacent cells meet, the hollow cylinders in the two membranes join from end to end, forming direct channels of communication between two cells. When the channel open, the connected cells function like a single cell that contains multiple nuclei (a syncytium)[2].