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: As well as T-tubules being a site for calcium entry into the cell, they are also a site for calcium removal. This is important as it means that calcium levels within the cell can be tightly controlled in a small area (i.e. between the T-tubule and sarcoplasmic reticulum, known as local control). Proteins such as the sodium-calcium exchanger and the sarcolemmal ATPase are located mainly in the T-tubule membrane. The sodium-calcium exchanger passively removes one calcium ion from the cell in exchange for three sodium ions. As a passive process it can therefore allow calcium to flow into or out of the cell depending on the combination of the relative concentrations of these ions and the voltage across the cell membrane (the electrochemical gradient ). The calcium ATPase removes calcium from the cell actively, using energy derived from adenosine triphosphate (ATP). Detubulation
In order to study T-tubule function, T-tubules can be artificially uncoupled from the surface membrane using a technique known as detubulation. Chemicals such as glycerol or formamide (for skeletal and cardiac muscle respectively) can be added to the extracellular solution that surrounds the cells. These agents increase the osmolarity of the extracellular solution, causing the cells to shrink. When these agents are withdrawn, the cells rapidly expand and return to their normal size.