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Content: The association of the T-tubule with a terminal cistern is known as a diad. [ 5]
In skeletal muscle cells, T-tubules are between 20 and 40 nm in diameter and are typically located either side of the myosin strip, at the junction of overlap between the A and I bands. T-tubules in skeletal muscle are associated with two terminal cisternae, known as a triad. [ 1][6]
Regulators[edit]
The shape of the T-tubule system is produced and maintained by a variety of proteins. The protein amphiphysin-2is encoded by the gene BIN1and is responsible for forming the structure of the T-tubule and ensuring that the appropriate proteins (in particular L-type calcium channels) are located within the T-tubule membrane.[7] Junctophilin-2 is encoded by the gene JPH2and helps to form a junction between the T-tubule membrane and the sarcoplasmic reticulum, vital for excitation-contraction coupling.[5] Titin capping protein or Telethonin is encoded by the gene TCAPand helps with T-tubule development and is potentially responsible for the increasing number of T-tubules seen as muscles grow. [ 5]
Function[edit]
Excitation-contraction coupling[edit]
See also: Excitation-contraction coupling
T-tubules are an important link in the chain from electrical excitation of a cell to its subsequent contraction (excitation-contraction coupling). When contraction of a muscle is needed, stimulation from a nerve or an adjacent muscle cell causes a characteristic flow of charged particlesacross the cell membrane known as an action potential. At rest, there are fewer positively charged particles on the inner side of the membrane compared to the outer side, and the membrane is described as being polarised. During an action potential, positively charged particles (predominantly sodium and calcium ions) flow across the membrane from the outside to the inside.