Molly Ayala
Gap junctions are membrane channels that form direct passageways between adjacent cells, allowing the exchange of small molecules, substrates, and metabolites. They are found between neurons and are often referred to as electrical synapses. These electrical synapses are highly dynamic and modifiable, and their strength is influenced by both gap junctional and non-junctional factors. Gap junctions facilitate electrical coupling by allowing the transfer of ions and electrical currents between cells, resulting in coordinated functions in various tissues. They are particularly important in cardiac muscle, enabling the heart muscle cells to contract in unison.
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What You'll Learn
Electrical synapses are dynamic and modifiable
Gap junctions electrically couple cells throughout the body of most animals. They are membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such as small molecules, substrates, and metabolites. A gap junction located between neurons is often referred to as an electrical synapse. Electrical synapses are present throughout the central nervous system and have been studied in various parts of the brain, such as the neocortex, hippocampus, and spinal cord.
The strength of electrical transmission through gap junctions is influenced by factors such as the conductance of the gap junction channels and the passive properties of the coupled neurons, including their resistance and capacitance. The impact of gap junctional currents on a neuron's excitability, or its "synaptic strength", is significantly influenced by non-junctional factors.
Additionally, the appearance of gap junctional coupling in the nervous system is developmentally regulated and persists after the establishment of chemical synapses. This suggests that gap junctions may play a functional role in cell-to-cell signaling, working alongside chemical transmission rather than serving as an alternative. The dynamic nature of electrical synapses is further highlighted by their ability to synchronize network activity in the brain and create chaotic network-level dynamics.
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Gap junctions facilitate intercellular signalling
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 formed by the docking of two ion channels or connexons, each contributed by a neighbouring cell, allowing the direct transfer of signalling molecules and providing a pathway of low resistance for the spread of electrical currents.
Gap junctions electrically couple cells throughout the body of most animals. Electrical coupling can be relatively fast-acting and can be used over short distances within an organism. Tissues in this section have well-known functions coordinated by gap junctions, with intercellular signalling happening in time frames of microseconds or less.
Gap junctions are particularly important in cardiac muscle. The signal to contract is passed efficiently through gap junctions, allowing the heart muscle cells to contract in unison. The importance is emphasised by a secondary ephaptic pathway for the signal to contract, which is also associated with the gap junction plaques. This redundancy in signal transmission associated with gap junction plaques is the first to be described and involves sodium channels rather than connexins.
The formation of gap junctions promotes communication between neighbouring myocytes, which facilitates the transfer of small molecules such as secondary messengers, metabolites, and small ions for electrical coupling. Gap junctions also help generate, propagate, and regulate neural oscillations, filter electrical signals, and can be modulated in a variety of ways.
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Electrical coupling is faster and shorter-ranged
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 formed by the docking of two ion channels or connexons, each contributed by a neighbouring cell, allowing the direct transfer of signalling molecules and providing a pathway of low resistance for the spread of electrical currents.
The strength of electrical coupling is affected by gap junctional and non-junctional factors. The amplitude of the "coupling potential" does not solely depend on the conductance of the gap junction channels but also on the passive properties determined by the resistance and capacitance of the coupled neurons.
The impact of gap junctional currents on a neuron's excitability, or its "synaptic strength", is dramatically influenced by non-junctional factors. For example, changes in the membrane resistance and capacitance of the postsynaptic neuron would also affect chemical synaptic transmission, but their influence seems more critical in the case of electrical synapses, which lack postsynaptic mechanisms of amplification of presynaptic signals.
In summary, electrical coupling via gap junctions is a fast and short-ranged process that facilitates intercellular communication and signalling within the body. The strength of electrical coupling is influenced by various factors, including the conductance of gap junction channels and the passive properties of coupled neurons.
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Gap junctions are important in cardiac muscle
Gap junctions are membrane channels between adjacent cells that allow the direct transfer of signalling molecules and provide a pathway for the spread of electrical current. They are formed by the docking of two ion channels or connexons, each contributed by a neighbouring cell.
Gap junctions have been found to play a role in cardiac conduction and heart morphogenesis. Studies have shown that changes in gap junction distribution, density, and properties may be involved in the initiation and persistence of various cardiac arrhythmias. For example, "gap junction remodelling", where connexins are reduced in number or redistributed, is considered arrhythmogenic.
Additionally, gap junctions are important in the development of the heart. Knockout mouse models with the Cx43 gene knocked out, for example, die neonatally from pulmonary outflow obstruction. This highlights the importance of gap junctions in the formation and function of the heart.
Overall, gap junctions are vital for the proper functioning of cardiac muscle, allowing for the coordinated contraction of heart muscle cells and helping to maintain a regular heartbeat.
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Gap junctions are formed by connexons
Gap junctions are membrane channels that electrically couple cells by allowing the direct exchange of small molecules, substrates, and metabolites. They are formed by the docking of two connexons, which are protein complexes composed of connexin proteins. Connexons connect one cell to another, and there are more than 26 types of connexin proteins.
Connexons are made up of two ion channels, each contributed by a neighbouring cell, which allow the direct transfer of signalling molecules and provide a pathway of low resistance for the spread of electrical currents. This electrical coupling can be relatively fast-acting and can be used over short distances within an organism.
The importance of gap junctions is particularly evident in cardiac muscle, where the signal to contract is passed efficiently through gap junctions, allowing the heart muscle cells to contract in unison. Gap junctions are also important in the uterine muscle (myometrium) during labour. The formation of gap junctions between individual myometrial cells promotes communication between neighbouring myocytes, facilitating the transfer of small molecules for electrical coupling.
Gap junctions are also referred to as electrical synapses, and they are found throughout the nervous system. They are best known for linking inhibitory neurons into large, effective networks within vertebrate brains. Electrical synapses are more dynamic and modifiable than generally perceived, and their strength is determined by both gap junctional and non-junctional factors.
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Frequently asked questions
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 sometimes referred to as electrical synapses.
Gap junctions are formed by the docking of two ion channels or connexons, contributed by neighbouring cells. This allows for the direct transfer of signalling molecules and provides a pathway for the spread of electrical currents.
Gap junctions electrically couple cells throughout the body of most animals. They are particularly important in cardiac muscle, allowing the signal to contract to pass efficiently, resulting in the heart muscle cells contracting in unison.
Neurons within the retina show extensive coupling. During labour, the myometrium (uterine muscle) increases expression of connexin-43, facilitating gap junction formation between individual myometrial cells. This promotes communication between neighbouring myocytes, facilitating the transfer of small molecules for electrical coupling.
