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: We will also consider the possible role of the t-tubules in the functional changes that occur during cardiac development, hypertrophy, and failure. Occurrence and Morphology of the T-Tubules
T-tubules are present in the cardiac tissue of all species of mammals so far investigated (eg, mice, 1 rats, 2 guinea pigs, 3 rabbits, 4 dogs, 5 pigs, 1 and humans 6) but appear to be absent in avian, 7 reptile 8 and amphibian 8 cardiac tissue. Within mammalian cardiac tissue, t-tubules occur predominantly in ventricular myocytes, being either absent or far less developed in atrial, pacemaking, and conducting tissue, 9 although a recent report has suggested that ≈50% of atrial myocytes possess a sparse irregular tubular system. 10 The following discussion will concentrate on mammalian ventricular myocytes. The t-tubules are invaginations of the sarcolemma and glycocalyx, which appears to remain associated with the sarcolemma within the t-tubules. 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.