Structure of Cardiac T-Tubules

action potential through the heart. During the cardiac action potential, Ca2+ enters each cardiac myocyte through L-type Ca2+ channels [as the Ca2+ current (ICa)] and activates adjacent Ca2+ release channels [ryanodine receptors (RyR)] in the membrane of the intracellular Ca2+ store, the sarcoplasmic reticulum (SR), causing Ca2+ release from the SR (5). Ventricular myocytes, which cause contraction of the ventricles of the heart, have invaginations of the surface membrane, called transverse (t-) tubules, which are important in ensuring rapid and synchronous contraction of the cell, and hence of the heart (13). This brief review will describe recent evidence that t-tubules are regions of the cell membrane that play a specialized role in transmembrane ion flux, and hence cell function, and that this role may change, and hence contribute to the altered function observed, during heart failure.