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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 emphasized by a secondary ephaptic pathway for the signal to contract also being associated with the gap junction plaques.
Interstitial cells of Cajal (ICC) are interstitial cells found in the gastrointestinal tract.There are different types of ICC with different functions. ICC and another type of interstitial cell, known as platelet-derived growth factor receptor alpha (PDGFRα) cells, are electrically coupled to smooth muscle cells via gap junctions, that work together as an SIP functional syncytium. [2]
Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle. Most smooth muscle is of the single-unit type, and is found in the walls of most internal organs (viscera); and lines blood vessels (except large elastic arteries), the urinary tract , and the digestive tract .
Gap junctions are collections of intercellular channels that allow ions and other tiny molecules to move directly between cells. [1] [14] These junctions are made up of a number of gap junction channels that consist of two connexons, each with six protein subunits called connexin, and a gene family of nearly 20 members encodes the connexins found in mammals [14] [15]
Smooth muscle effectors are bundles rather than single cells, that are connected by gap junctions which allow electrotonic spread of activity between cells. Many smooth muscle cells in a transverse section through a muscle bundle show regions of very close apposition to adjacent cells at which connexins form junctions between the cells.
The muscle cell that makes up animal skeletal muscle is a classic example of a syncytium cell. The term may also refer to cells interconnected by specialized membranes with gap junctions, as seen in the heart muscle cells and certain smooth muscle cells, which are synchronized electrically in an action potential.
Intercalated discs are complex structures that connect adjacent cardiac muscle cells. The three types of cell junction recognised as making up an intercalated disc are desmosomes, fascia adherens junctions, and gap junctions. [2] Fascia adherens are anchoring sites for actin, and connect to the closest sarcomere. [3]
Gap junctions have been demonstrated in rare circumstances as one coupling mechanism between ICC and smooth muscle cells. [6] Another potential coupling mechanism is the "Peg and Socket" theory which demonstrates that the membranes of smooth muscle cells have the ability either form physical narrow "sockets" or "pegs" to lock onto other smooth ...