Gap junction

Gap Junction

Diagram of a gap junction.

Gap junctions are specialized intercellular connections that facilitate direct communication between cells. They are crucial for maintaining tissue homeostasis and enabling coordinated cellular functions. Gap junctions are composed of connexin proteins that form channels allowing the passage of ions, metabolites, and other small molecules between adjacent cells.

Structure

Gap junctions are formed by the alignment of two hemichannels, or connexons, from adjacent cells. Each connexon is composed of six connexin subunits. The connexins are integral membrane proteins that span the lipid bilayer four times, creating a pore in the center. The alignment of connexons from neighboring cells forms a continuous aqueous channel that bridges the intercellular space.

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Historical depiction of gap junction structure.

Function

Gap junctions play a vital role in cell communication by allowing the direct transfer of signaling molecules and ions. This direct communication is essential for various physiological processes, including cardiac muscle contraction, neuronal signaling, and embryonic development. Gap junctions also contribute to the maintenance of tissue homeostasis by enabling the distribution of nutrients and waste products.

Connexin Diversity

There are multiple types of connexins, each encoded by a different gene. The diversity of connexins allows for the formation of gap junctions with distinct properties, such as permeability and regulatory mechanisms. Different tissues express specific connexins, which tailor the gap junctions to the functional needs of the tissue.

Phylogenetic tree of pannexins, related to connexins.

Regulation

The permeability and function of gap junctions are regulated by various factors, including pH, calcium concentration, and phosphorylation of connexins. These regulatory mechanisms ensure that gap junction communication is modulated in response to physiological changes and cellular needs.

Pathophysiology

Dysfunction of gap junctions is implicated in several diseases, including cardiac arrhythmias, neuropathies, and certain types of cancer. Mutations in connexin genes can lead to impaired gap junction communication, contributing to the pathogenesis of these conditions.

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Dye diffusion assay used to study gap junction communication.

Gap Junctions in the Lens

Gap junctions are particularly important in the lens of the eye, where they facilitate the transport of nutrients and ions between lens fibers. This communication is essential for maintaining lens transparency and function.

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3D map of lens showing gap junction distribution.

Gap Junctions in the Heart

In cardiac tissue, gap junctions are critical for the propagation of electrical impulses, ensuring synchronized contraction of the heart muscle. Alterations in gap junction expression or function can lead to arrhythmias and other cardiac disorders.

Perinexial ephaptic coupling in cardiac tissue.

Gap Junctions in the Epithelium

In epithelial tissues, gap junctions contribute to barrier function and coordinated cellular responses to environmental stimuli. They are involved in processes such as wound healing and epithelial cell differentiation.

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Expression of Cx50 in epithelial cells.

Related Pages

• Connexin
• Intercellular junctions
• Cell communication
• Cardiac conduction system