Trystan Casey
Gap junctions are membrane channels that bridge a 2-4 nm gap between cell membranes, allowing the direct exchange of cytoplasmic substances such as small molecules, substrates, and metabolites. They are composed of two hemichannels called connexons, which are made up of connexin proteins. Gap junctions are found in most or all tissues and are particularly important in cardiac muscle, allowing the signal to contract to be passed efficiently so that heart muscle cells contract in unison. They are also found in the brain, where they are called electrical synapses. Electrical synapses occur at what are called gap junctions, providing a direct pathway for the spread of electrical currents between cells.
| Characteristics | Values |
|---|---|
| Definition | Gap junctions are membrane channels between adjacent cells that allow the direct exchange of electrical impulses, small molecules, substrates, and metabolites. |
| Function | Gap junctions function as a direct cell-to-cell pathway for electrical currents, small molecules, and ions. |
| Location | Gap junctions are found in most or all tissues and are present throughout the central nervous system. |
| Structure | Gap junctions are composed of protein complexes called connexons, which are made up of connexin proteins. |
| Connexons | Each gap junction contains two connexons, each contributed by one cell at the synapse. Connexons are formed by six connexin proteins. |
| Connexins | There are more than 26 types of connexin and at least 12 non-connexin components that make up the gap junction complex. |
| Pore Size | The pore of a gap junction channel has a lumen diameter of about 1.2 to 2.0 nm, allowing the passage of ions and small to medium-sized molecules. |
| Electrical Transmission | Electrical transmission through gap junctions is faster than chemical transmission and occurs without the involvement of neurotransmitters. |
| Bidirectionality | Gap junctions are mostly bidirectional, allowing impulse transmission in both directions between cells. |
| Regulation | Gap junction regulation involves the interaction of gap junction channels with scaffold and regulatory proteins. |
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![[(Gap Junctions: Gap Junctions Molecular Basis of Cell Communication in Health and Disease Vol 49: Molecular Basis of Cell Communication in Health and Disease)] [Author: Dale J. Benos] published on (August, 2000)](https://m.media-amazon.com/images/I/41wwGX4+ZhL._AC_UY218_.jpg)
What You'll Learn
- Gap junctions are membrane channels that allow the exchange of ions, small molecules, and electrical impulses
- They are formed by connexons, which are composed of connexin proteins
- Gap junctions are found in most or all tissue, including the brain, where they are called electrical synapses
- They are involved in the development of cell polarity and left-right symmetry in animals
- Gap junctions are important for the synchronous firing of neurons and muscle contraction
Gap junctions are membrane channels that allow the exchange of ions, small molecules, and electrical impulses
Gap junctions are formed by two connexons, each contributed by one cell. Connexons are made up of six connexin proteins, which may be identical or slightly different. Gap junctions facilitate the direct exchange of cytoplasmic substances, including small molecules, substrates, and metabolites. They bridge a 2-4 nm gap between cell membranes.
The connexin proteins that make up gap junctions are structurally homologous between vertebrates and invertebrates but differ in sequence. There are more than 26 types of connexin, as well as at least 12 non-connexin components that make up the gap junction complex, or nexus. These include the tight junction protein ZO-1, which holds membrane content together and adds structural clarity to a cell, as well as sodium channels and aquaporin.
Gap junctions are the morphological substrate of one class of electrical synapse. Electrical synapses are found throughout the central nervous system and are particularly important in neural systems that require the fastest possible response, such as defensive reflexes. They allow for more rapid signaling than chemical synapses because there is no electrical-to-chemical-to-electrical transition necessary.
The bidirectional nature of electrical synapses allows impulse transmission in either direction, and the low resistance of gap junctions enables the spread of ionic currents between neurons. This electrical coupling can be relatively fast-acting and is used over short distances within an organism.
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They are formed by connexons, which are composed of connexin proteins
Gap junctions are membrane channels that allow the direct exchange of electrical currents, small molecules, ions, and metabolites between adjacent cells. They are found in most or all tissues and are particularly important in cardiac muscle.
Gap junctions are formed by connexons, which are composed of connexin proteins. Connexins are the core proteins of gap junction channels and are synthesized on ER-bound ribosomes. They are then inserted into the ER cotranslationally, followed by oligomerization into connexons. Connexons are delivered to the membrane via the actin or microtubule networks, where they may remain as hemichannels or dock with compatible connexons on adjacent cells to form gap junctions.
The term connexin refers to the molecular weight of the protein, for example, connexin43=GJA1, connexin30.3=GJB4. There are more than 26 types of connexin, and they can be classified into three groups (A, B, and C) or into α, β, and γ subgroups based on molecular weight and the length of the cytoplasmic domain. Connexins with molecular weights of 26 kDa, 32 kDa, and 43 kDa, for instance, are referred to as Cx26, Cx32, and Cx43, respectively.
When identical connexin proteins join to form a connexon, it is called a homomeric connexon, and when different connexin proteins join, it is called a heteromeric connexon. Two connexons, joined across a cell membrane, form a gap junction channel. The connexin proteins have a very short half-life, so the synthesis and delivery of new connexin proteins are coupled with the simultaneous internalization and degradation of gap junctions and connexins.
In vertebrates, two pairs of six connexin proteins form a connexon, while in invertebrates, six innexin proteins form an innexon. The connexin genes (DNA) are transcribed to RNA, which is then translated to produce a connexin.
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Gap junctions are found in most or all tissue, including the brain, where they are called electrical synapses
Gap junctions are membrane channels that allow the direct exchange of electrical currents, small molecules, substrates, and metabolites between adjacent cells. They are found in most or all tissues in the body of most animals, electrically coupling cells and facilitating intercellular signalling.
In the brain, gap junctions are called electrical synapses. Electrical synapses occur throughout the central nervous system and have been studied in the neocortex, hippocampus, thalamic reticular nucleus, locus coeruleus, inferior olivary nucleus, mesencephalic nucleus of the trigeminal nerve, olfactory bulb, retina, and spinal cord of vertebrates. They are also found in the striatum, cerebellum, and suprachiasmatic nucleus.
Electrical synapses are formed by gap junction channels, which are composed of two hemichannels called connexons. Each connexon is made up of six connexin proteins. Gap junctions allow for direct electrical communication between cells, and the transmission of electrical impulses without the need for transduction. This results in very fast communication, with neurons that are electrically coupled tending to have nearly synchronous electrical activity.
The role of neuronal gap junctions is often associated with providing a pathway for the spread of ionic currents between neurons, generally referred to as electrical coupling. Gap junctions are particularly important in cardiac muscle, allowing the signal to contract to be passed efficiently so that the heart muscle cells contract in unison.
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They are involved in the development of cell polarity and left-right symmetry in animals
Gap junctions are membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such as small molecules, substrates, and metabolites. They are composed of two hemichannels called connexons, which are made up of six connexin proteins. Gap junctions are found in most or all tissues and are particularly important in cardiac muscle, allowing the heart muscle cells to contract in unison.
Gap junctions are also key in the development of cell polarity and left-right symmetry in animals. Systematic studies have shown that gap junctions play a crucial role in the differentiation of cells and the determination of the position of body organs. By allowing direct electrical communication between cells, gap junctions enable the coordination of tissue functions with intercellular signaling happening in time frames of microseconds or less.
In the nervous system, gap junctions are called electrical synapses and are found in the brain, retina, spinal cord, and other areas. Electrical synapses are faster than chemical synapses because they do not involve neurotransmitters or synaptic delay. They are often found in neural systems that require the fastest possible response, such as defensive reflexes. Electrical synapses are also bidirectional, allowing impulse transmission in either direction.
The strength of electrical coupling at gap junctions is influenced by both gap junctional factors (gap junctional conductance) and non-junctional factors (passive and active neuronal properties). The dynamic regulation of gap junctional conductance by neurotransmitter modulators and nearby glutamatergic synaptic activity further highlights the complexity of these structures.
Overall, gap junctions are essential for the development of cell polarity and left-right symmetry in animals, facilitating electrical communication and coordination between cells in various tissues and systems throughout the body.
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Gap junctions are important for the synchronous firing of neurons and muscle contraction
Gap junctions are membrane channels that bridge a 2-4 nm gap between the membranes of adjacent cells. They are composed of protein complexes called connexons, which are made up of connexin proteins. Gap junctions allow for the direct exchange of electrical currents, small molecules, substrates, and metabolites between cells.
In the context of electrical impulses, gap junctions are important for the synchronous firing of neurons. They act as electrical synapses, providing a direct pathway for the spread of electrical currents between neurons. This electrical coupling allows for nearly synchronous electrical activity between neurons, enabling them to act as a syncytium. Gap junctions are particularly important in situations that require a fast response, such as defensive reflexes, as they facilitate rapid signaling without the need for electrical-to-chemical-to-electrical transitions.
The role of gap junctions in neuronal communication was first investigated in the 1980s, and it was found that blocking gap junctions in embryonic cells disrupted normal development. Further studies have shown that gap junctions are involved in the development of cell polarity and left-right symmetry in animals. Additionally, gap junctions are key in signaling that determines the position of body organs.
In the context of muscle contraction, gap junctions are crucial in the heart, where they enable the efficient transmission of the signal to contract. This allows heart muscle cells to contract in unison, ensuring the proper functioning of the heart. Gap junctions are also found in other muscle tissues, such as the striatum and cerebellum, and are involved in nerve-to-muscle impulses, contributing to muscle contraction.
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Frequently asked questions
Gap junctions are membrane channels between adjacent cells that allow the direct exchange of electrical currents, small molecules, substrates, and metabolites.
Gap junctions are formed by two connexons, each composed of a ring of six connexin proteins. Gap junctions allow for direct electrical communication between cells.
Gap junctions electrically couple cells throughout the body of most animals. Gap junctions are particularly important in cardiac muscle, allowing the signal to contract to be passed efficiently through gap junctions so that the heart muscle cells contract in unison.
Gap junctions are found in most or all tissue, and in the brain, they are called electrical synapses. Gap junctions are also found in the neocortex, hippocampus, thalamic reticular nucleus, and the spinal cord of vertebrates.
Gap junctions were first described as close appositions alongside tight junctions, however, electron microscopy studies in 1967 led to gap junctions being named as such to be distinguished from tight junctions. Gap junctions bridge a 2-4 nm gap between cell membranes, whereas tight junctions are protein complexes that hold membrane content together and add structural clarity to a cell.
