A hemichannel is essentially one half of a gap junction channel, which can function independently and perform distinct physiological roles. These hemichannels are primarily made of connexins, but can also be formed by pannexins, which are proteins similar to invertebrate gap junction proteins.
Hemichannels Explained
Think of gap junctions as bridges between cells. A hemichannel is half of that bridge, residing on the membrane of one cell. When two hemichannels from neighboring cells dock together, they form a complete gap junction channel, allowing direct communication between the cells. However, hemichannels don't always need to be connected to another cell to perform their job.
Composition: Connexins and Pannexins
The building blocks of hemichannels are proteins.
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Connexins: These are the most well-known proteins that form hemichannels.
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Pannexins: These proteins are homologous to invertebrate gap junction proteins, and they can also assemble to form hemichannels.
Independent Roles: Beyond Gap Junctions
While hemichannels contribute to gap junction communication, they also have independent functions. This means they can operate and influence cellular processes even when they're not connected to a hemichannel on another cell. This is significant because it expands their role beyond simple cell-to-cell communication.
Hemichannel vs. Gap Junction Channel
To clarify the difference:
| Feature | Hemichannel | Gap Junction Channel |
|---|---|---|
| Structure | One half of a complete channel | Formed by two docked hemichannels |
| Location | Plasma membrane of a single cell | Bridge between two adjacent cells |
| Primary Proteins | Connexins, Pannexins | Connexins, Pannexins |
| Function | Can function independently; contributes to gap junction formation. | Facilitates direct communication between cells |
