Title: T-Tubule Function in Mammalian Cardiac Myocytes | Circulation Research
Headings: T-Tubule Function in Mammalian Cardiac Myocytes
T-Tubule Function in Mammalian Cardiac Myocytes
Abstract
Occurrence and Morphology of the T-Tubules
T-Tubule Development Is Labile
Proteins Present in the T-Tubule Membrane
Ca2+-Handling Proteins
Na+-Handling Proteins
K+-Handling Proteins
Anion-Handling Proteins
Second-Messenger Pathways
Interpretation of Immunohistochemical Data
Protein Colocalization Within, and With Proteins Adjacent to, the T-Tubules
Localization of Function
Cells Lacking T-Tubules
Diffusion Studies
Scanning Pipette
Detubulation
Functional Role
Electrical Properties of T-Tubules
Coupling of Ca 2+ Entry and Ca 2+ Release
Ca 2+ Efflux
Signal Transduction
Changes During Development and Disease
T-Tubule Development and Morphology in Hypertrophy and Failure
Changes in Protein Expression in Development, Hypertrophy, and Failure
Relevance of Changes in T-Tubule Structure and Protein Expression to Function
Conclusions and Unanswered Questions
Footnotes
References

Content: 11 Early studies of cardiac muscle showed that they occur at the Z line, at the end of each sarcomere 12; therefore, they occur at intervals of ≈2 μm along the longitudinal axis of the ventricular myocyte. Subsequent studies have shown that the t-tubular system also has longitudinal extensions. 13 Although the t-tubules leave the surface membrane at the Z line, forming an approximately rectangular array, only ≈60% of the tubular volume occurs near the Z line; the other 40% occurs between the Z lines. 2 Thus, the t-tubular system is not, as its name might suggest, a simple transverse system of tubules but is a complex system of branching tubules with both transverse and longitudinal elements ( Figure 1 ). Because of its complexity, it has been suggested that the transverse-axial tubular system, 14 sarcolemmal Z rete, 2 or sarcolemmal tubule network 11 might be a more appropriate name. However, t-tubule remains the standard term and will be used in the present review, and surface sarcolemma will be used to describe that part of the cell membrane not within the t-tubules. Download figure
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Figure 1. Three-dimensional structure of the t-tubular system in a living rat ventricular myocyte, reconstructed from a stack of images of dextran-linked fluorescein fluorescence within the t-tubules.