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The longitudinal SR are thinner projects, that run between the terminal cisternae/junctional SR, and are the location where ion channels necessary for calcium ion absorption are most abundant. [4] These processes are explained in more detail below and are fundamental for the process of excitation-contraction coupling in skeletal , cardiac and ...
There are several mechanisms directly linked to the terminal cisternae which facilitate excitation-contraction coupling. When excitation of the membrane arrives at the T-tubule nearest the muscle fiber, a dihydropyridine channel (DHP channel) is activated. [2] This is similar to a voltage-gated calcium channel, but is not actually an ionotropic ...
The shape of the T-tubule system is produced and maintained by a variety of proteins. The protein amphiphysin-2 is encoded by the gene BIN1 and 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. [9]
In between two terminal cisternae is a tubular infolding called a transverse tubule (T tubule). T tubules are the pathways for action potentials to signal the sarcoplasmic reticulum to release calcium, causing a muscle contraction. Together, two terminal cisternae and a transverse tubule form a triad. [58]
The cisternae are shaped by the cytoskeleton of the cell through a lipid bilayer. [4] Post-translational modifications such as glycosylation, phosphorylation and cleavage occur in the Golgi and as proteins travel through it, they go through the cisternae, which allows functional ion channels to be created due to these modifications. [5]
Excitation-contraction coupling in myocardium relies on sarcolemma depolarization and subsequent Ca 2+ entry to trigger Ca 2+ release from the sarcoplasmic reticulum.When an action potential depolarizes the cell membrane, voltage-gated Ca 2+ channels (e.g., L-type calcium channels) are activated.
L-type calcium channels are also enriched in the t-tubules of striated muscle cells, i.e., skeletal and cardiac myofibers. When these cells are depolarized, the L-type calcium channels open as in smooth muscle. In skeletal muscle, the actual opening of the channel, which is mechanically gated to a calcium-release channel (a.k.a. ryanodine ...
The plasma membrane protein "Orai" (ORAI1 and ORAI2 in humans) forms the pore of the CRAC channel. The protein ORAI1 is a structural component of the CRAC calcium channel. ORAI1 interacts with the STIM1 protein. STIM1 is a transmembrane protein of the endoplasmic reticulum (ER). STIM1 can sense the concentration of Ca 2+ inside the ER.