Module 7: Figure ventricular junctional zone
Structural organization of the junctional zones in ventricular cardiac cells.
These electron micrographs illustrate the structural organization of the junctional zone and its relationship to the striated contractile fibres and mitochondria. (A) The arrowheads point to the T-tubules (T) lined up with the dark Z disc of the contractile elements. (B) Detail of a T-tubule with flattened sacs of junctional sarcoplasmic reticulum (jSR) indicated by the arrowheads. (C) Details of the free sarcoplasmic reticulum (fSR) running between the contractile fibres. (D) A tangential view at the level of the Z line illustrates how the contractile fibres are surrounded by jSRs (bracketed by arrowheads). (E) The arrows point to striations that are the ryanodine receptors that span the gap between the jSR and T tubule. (F) This drawing illustrates the relationship between the jSR, fSR and the T-tubule (T). Reproduced from Brochet, D.X.P., Yang, D., Di Maio, A.D., Lederer, W.J., Franzini-Armstrong, C. and Cheng, H. (2005) Ca2+ blinks: rapid nanoscopic store calcium signaling. Proc. Natl. Acad. Sci. U.S.A. 102:3099–3104. Copyright (2005) National Academy of Sciences, U.S.A; see Brochet et al. 2005.