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: Ca2+-Handling Proteins
The location of sarcolemmal Ca 2+ -handling proteins is important because of their role in excitation-contraction coupling and because the Ca 2+ -release channels (ryanodine receptors [RyRs]) of the sarcoplasmic reticulum (SR) are concentrated close to the t-tubule (see Protein Colocalization Within, and With Proteins Adjacent to, the T-Tubules). In the rabbit heart, an early study showed that a membrane fraction from the t-tubules had a higher density of L-type Ca 2+ channels than did membrane from the surface sarcolemma. 21 A more recent immunologic study also found this channel to be concentrated in the t-tubules of adult rabbit ventricular myocytes, with less staining of the surface sarcolemma, although the surface staining that did occur was punctate and associated with junctional SR. 22 In rat heart, the L-type Ca 2+ channel, and hence current ( ICa ), is also concentrated in the t-tubules, with estimates ranging from 3 to 9 times more concentrated in the t-tubule membrane than on the surface sarcolemma. 23–26 Comparative studies suggest that the t-tubular concentration of the L-type Ca 2+ channel is greater in rat ventricular myocytes than in those from the rabbit. 22
Although a high density of L-type Ca 2+ channel at the Z line has been reported in all studies of which we are aware, it has also been reported tha