t-Tubules and sarcoplasmic reticulum function in cardiac ventricular myocytes.
Although the existence of t-tubules in mammalian cardiac ventricular myocytes has been recognized for a long time, it now appears that their structure and function are more complex than previously believed. Recent work has provided evidence that many of the key proteins underlying excitation-contraction coupling are located predominantly at the t-tubules. L-type Ca(2+) current (I(Ca)) flowing across the t-tubule membrane provides a rapidly inactivating Ca(2+) influx that triggers Ca(2+) release from the sarcoplasmic reticulum (SR), thereby allowing rapid and synchronous Ca(2+) release throughout the cell; I(Ca) at the t-tubules also appears to be more sensitive than that at the surface membrane to regulation by beta-adrenergic stimulation and intracellular Ca(2+). In contrast, although its density is lower, I(Ca) flowing across the surface membrane inactivates slowly, and thus may help load the SR with Ca(2+). There is also increasing evidence that many of the mechanisms that remove Ca(2+) from the cytoplasm are located predominantly at the t-tubules, which therefore play an important role in determining cellular, and hence SR, Ca(2+) content. Thus, the t-tubules appear to play a central role in the increase and subsequent decrease of Ca(2+) during the systolic Ca(2+) transient. Remodelling of the t-tubules has been reported in cardiac pathologies, and may play a role in the altered cellular, and hence cardiac, function observed in such conditions.
Orchard
Clive
C
Department of Physiology, University of Bristol, Bristol, BS8 1TD, UK. clive.orchard@bristol.ac.uk
Brette
Fabien
F
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000502:physiology; D006352:Heart Ventricles / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D032383:Myocytes, Cardiac / Q000502:physiology* / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000502:physiology*; D019831:Sodium-Calcium Exchanger / Q000502:physiology
D020746:Calcium Channels, L-Type; D019831:Sodium-Calcium Exchanger; D000252:Calcium-Transporting ATPases; D002118:Calcium