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: One region of membrane depolarises adjacent regions, and the resulting wave of depolarisation then spreads along the cell membrane. The polarisation of the membrane is restored as potassium ions flow back across the membrane from the inside to the outside of the cell. In cardiac muscle cells, as the action potential passes down the T-tubules it activates L-type calcium channels in the T-tubular membrane. Activation of the L-type calcium channel allows calcium to pass into the cell. T-tubules contain a higher concentration of L-type calcium channels than the rest of the sarcolemma and therefore the majority of the calcium that enters the cell occurs via T-tubules. This calcium binds to and activates a receptor, known as a ryanodine receptor, located on the cell's own internal calcium store, the sarcoplasmic reticulum. Activation of the ryanodine receptor causes calcium to be released from the sarcoplasmic reticulum, causing the muscle cell to contract. In skeletal muscle cells, however, the L-type calcium channel is directly attached to the ryanodine receptor on the sarcoplasmic reticulum allowing activation of the ryanodine receptor directly without the need for an influx of calcium. The importance of T-tubules is not solely due to their concentration of L-type calcium channels, but lies also within their ability to synchronise calcium release within the cell. The rapid spread of the action potential along the T-tubule network activates all of the L-type calcium channels near-simultaneously.