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 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. Sign in to download full-size image
Figure 53.2. The SR, seen after Golgi “staining” (A) and in standard thin section (B), forms a complex, continuous network that surrounds the myofibrils. In these fibers from the frog the T-tubules (vertical arrows in B) are located at the Z-lines. The junctional domains of the SR (jSR, oblique arrows) are wide, contain calsequestrin and directly face the T-tubules. The triads are the sites of calcium release during muscle activation and thus they are also called calcium release units (CRUs).