Title: T-tubule - Wikipedia
Headings: T-tubule
T-tubule
Contents
Structure
Regulators
Function
Excitation-contraction coupling
Calcium control
Detubulation
History
Clinical significance
See also
References

Content: Due to this complex orientation, some refer to T-tubules as the transverse-axial tubular system. The inside or lumen of the T-tubule is open at the cell surface, meaning that the T-tubule is filled with fluid containing the same constituents as the solution that surrounds the cell (the extracellular fluid). Rather than being just a passive connecting tube, the membrane that forms T-tubules is highly active, being studded with proteins including L-type calcium channels, sodium-calcium exchangers, calcium ATPases and Beta adrenoceptors. T-tubules are found in both atrial and ventricular cardiac muscle cells ( cardiomyocytes ), in which they develop in the first few weeks of life. They are found in ventricular muscle cells in most species, and in atrial muscle cells from large mammals. In cardiac muscle cells, T-tubules are between 20 and 450 nanometers in diameter and are usually located in regions called Z-discs where the actin filaments anchor within the cell. T-tubules within the heart are closely associated with the intracellular calcium store known as the sarcoplasmic reticulum in specific regions referred to as terminal cisternae. The association of the T-tubule with a terminal cistern is known as a diad. 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.