Are T-tubules part of the sarcoplasmic reticulum?

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. T-tubules in skeletal muscle are associated with two terminal cisternae, known as a triad.

What is the role of the T-tubules?

T-tubules are invaginations of the plasma membrane, which are present exclusively in striated muscle. Their role is to maintain the SR calcium store under the tight control of membrane depolarization via the voltage sensor channel DHPR [2].

What happens when T-tubules are depolarized?

Waves of depolarization on the muscle cell surface descend to the myobrils via transverse T tubules, which are continuous with the surface cell membrane and pass into the muscle cell at the junctions between the thick and thin myofilaments. As a result, the concentration of Ca2+ ions around the myofilaments rises.

Do T-tubules release calcium?

Cardiac muscle cells also depend on extracellular calcium ions, that enter through the T-tubules and triggers release of calcium ions from the SR.

How big are the T tubules of cardiac muscle?

The t-tubules of cardiac muscle have a mean diameter of ≈200 to 300 nm, 13 although within a single rat ventricular myocyte, the diameter of individual tubules can vary from 20 to 450 nm, but with more than half the t-tubules having diameters between 180 and 280 nm.

Where are the transverse tubules located in the heart?

Unique to striated muscle cells, transverse tubules (t-tubules) are membrane organ- elles that consist of sarcolemma penetrating into the myocyte interior, forming a highly branched and interconnected network. Mature t-tubule networks are found in mam- malian ventricular cardiomyocytes, with the transverse components of t-tubules occurring near

Why are T tubules important to cardiac cell function?

Thus, the t-tubules are an important determinant of cardiac cell function, especially as the main site of excitation-contraction coupling, ensuring spatially and temporally synchronous Ca 2+ release throughout the cell.

Where are the T-tubules located in muscle cells?

Specific to striated muscle cells, t-tubules are invaginations of the sarcolemma, penetrating into the intracellular space of myocytes. These tubular invaginations form a complex network with transverse tubules that are interconnected within the cytoplasm by longitudinal tubules.