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T-tubules (transverse tubules) are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells.With membranes that contain large concentrations of ion channels, transporters, and pumps, T-tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration.
Within the t-tubules, distinct ion channels and cellular proteins are present within the t- tubule bilayer that allow movement of calcium influx from the extracellular space into the myocyte to initiate depolarization and contraction. Once traveling through the t- tubules, the calcium arrives at the sarcoplasmic reticulum.
The conduction of action potentials along the T-tubules stimulates the opening of voltage-gated Ca 2+ channels which are mechanically coupled to Ca 2+ release channels in the sarcoplasmic reticulum. [9] The Ca 2+ then diffuses out of the sarcoplasmic reticulum to the myofibrils so it can stimulate contraction. The endplate potential is thus ...
The α 1 subunit of T-type channels is the primary subunit that forms the pore of the channel, and allows for entry of calcium. T-type calcium channels function to control the pace-making activity of the SA Node within the heart and relay rapid action potentials within the thalamus. These channels allow for continuous rhythmic bursts that ...
In skeletal muscle, there is a very high concentration of L-type calcium channels, situated in the T-tubules. Muscle depolarization results in large gating currents, but anomalously low calcium flux, which is now explained by the very slow activation of the ionic currents.
Early in development, there is a high amount of expression of T-type calcium channels. During maturation of the nervous system, the expression of N or L-type currents becomes more prominent. [15] As a result, mature neurons express more calcium channels that will only be activated when the cell is significantly depolarized.
It senses the voltage change caused by the end-plate potential from nervous stimulation and propagated by sodium channels as action potentials to the T-tubules. It was previously thought that when the muscle depolarises, the calcium channel opens, allowing calcium in and activating RyR1, which mediates much greater calcium release from the ...
This is followed by a hyperpolarization-activated "sag" current that contributes to slowly depolarizing the membrane potential. An inward Ca 2+ current through T-type calcium channels is the last phase, and the main current responsible for the large transient depolarization. This overrides the other currents once T-type channels are activated.