Title: T-Tubule - an overview | ScienceDirect Topics
Headings: T-Tubule
T-Tubule
Ion Channel Trafficking
T-Tubules
Skeletal Muscle
T-tubules Are Surface Invaginations; the SR Is an Internal Membrane System
Structure and Function of Calcium Release Channels
2 T Tubules and CRUs Revert to More Primitive Forms Under Pathological Conditions
Muscles
Coupling Action Potentials to Contraction
The Cellular Basis of Cardiac Contractility
The SR Releases Stored Ca 2+ to Activate Contraction
Disorders of Muscle Excitability
Calcium couples muscle membrane excitation to filament contraction
Muscle physiology
Excitation–contraction coupling
EXERCISE | Muscle
Voltage-dependent Sarcoplasmic Reticulum Ca 2+ Release

Content: The mature position of T-tubules within planes perpendicular to the fiber long axis (Figure 53.1A,B) is acquired gradually during the coordinated differentiation of myofibrils and membrane system. This reorientation takes up to a month in chick and mouse muscles and the association of the whole triad assembly with the appropriate myofibril location drives it, perhaps via ankyrin and the giant protein obscurin. However, longitudinal remnants of the T network are still present in the adult. The T-tubules actually carry an action potential in some but perhaps not all fibers, but a depolarization of the tubules rather than the action potential is a triggering event in EC coupling (7). The initial description of the SR (2) correctly identified this organelle as a differentiated form of the ubiquitous endoplasmic reticulum (ER), characterized by its abundance and its precise positioning and relationship to the myofibrils ( Figure 53.2 ). The SR is composed of elements that repeat longitudinally with a period equal to that of the sarcomere. In the case of frog muscle, shown in Figure 53.2, for example, the SR shows a network of longitudinal elements opposite the A band, connected to the two enlarged cisternae on either side of the Z-line. The T-tubules are located in the space between the two SR cisternae ( Figure 53.2B) and the assembly of two SR and one T-tubule is called a triad. The SR, like the ER, is a totally internal membrane system that creates a segregated space: its lumen is not connected to either the cytoplasm or the extracellular space.