Module 3: Figure hemichannels and gap junctions
Hemichannels and gap junctions.
Members of the connexin and pannexin families are membrane proteins that have similar transmembrane topologies with four transmembrane domains with the N- and C-termini located in the cytoplasm. Six of the pannexin subunits come together to form pannexons, whereas a similar assembly of connexins is known as a connexon. Pannexons and connexons form membrane channels with different functions. The pannexon, which is also known as a hemichannel, is activated by Ca2+ to release components from the cytosol such as ATP and glutamate. On the other hand, the connexons from neighbouring cells interact with each other to form gap junctions that act as intercellular channels permeable to ions and second messengers such as cyclic AMP and InsP3.