Membrane channels are a family of
biological membrane
A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates the interior of a cell from the external environment or creates intracellular compartments by serving as a boundary between one part of the ce ...
proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
which allow the passive movement of
ions (
ion channels
Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...
),
water (
aquaporins) or other
solutes to passively pass through the membrane down their
electrochemical gradient. They are studied using a range of
channelomics experimental and mathematical techniques. Insights have suggested
endocannabinoids (eCBs) as
molecules
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
that can regulate the opening of these channels during diverse conditions.
Properties
Hemichannels
A hemichannel is a membrane channel made up of six subunits.
A hemichannel is defined as one-half of a
gap junction
Gap junctions are specialized intercellular connections between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulate ...
channel.
Hemichannels consist of
connexins.
Pannexin
Pannexin
Pannexins (from Greek 'παν' — all, and from Latin 'nexus' — connection) are a family of vertebrate proteins identified by their homology to the invertebrate innexins. While innexins are responsible for forming gap junctions in invertebr ...
s are involved in the process of
purinergic signalling. They release
adenosine triphosphate (ATP), which activate
purinergic receptor
Purinergic receptors, also known as purinoceptors, are a family of plasma membrane molecules that are found in almost all mammalian tissues. Within the field of purinergic signalling, these receptors have been implicated in learning and memory, lo ...
s. On the other hand, purinergic receptor activation can also lead to the opening of the channel, via a
positive feedback loop.
In addition,
P2Y receptor
P2Y receptors are a family of purinergic G protein-coupled receptors, stimulated by nucleotides such as adenosine triphosphate, adenosine diphosphate, uridine triphosphate, uridine diphosphate and UDP-glucose.To date, 8 P2Y receptors have been c ...
s activate
inositol trisphosphate, which leads to a transient increase in intracellular
calcium, and opens both connexin and pannexin channels, therefore contributing to the propagation of
calcium waves across
astrocytes and
epithelial cells.
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References
Further reading
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{{Ion channels
Membrane biology