Sarcoplasmic reticulum gene expression in cardiac hypertrophy and heart failure.

Structure of the Cardiac SRThe SR is an intracellular membrane network that is in close contact with the myofibrils and couples with the sarcolemma through transverse tubules (T tubules).The structure of the SR in cardiac muscle is very similar to that described in skeletal muscle (reviewed in Refer- ence 6).As in skeletal muscle, the cardiac SR is composed of two main components: the junctional SR (terminal cisternae) and the longitudinal tubules.How- ever, the structure of the cardiac SR is not as well organized in relation to the T tubule.7There are relatively few T tubules in cardiac muscle, and they are, in general, of large diameter.They are often coupled on only one side to the terminal cisternae, forming a dyad rather than a triad.Interestingly, many of these single couplings or dyads occur between the terminal cisternae and the sarcolemma.In avian ventricular myocytes, 80% of the terminal cisternae (corbular SR) are not associ-