Module 7: Figure SA node junctional zone
Sinoatrial node junctional zone between the sarcolemma and sarcoplasmic reticulum (SR).
The electron micrograph on the left illustrates a contact between two sinoatrial cells. Note the thin stacks of sarcoplasmic reticulum (SR) membranes closely apposed to the sarcolemma. The diagram on the right shows how Ca2+ released from the SR is directed towards the sarcolemma, which has an array of channels and Na+/Ca2+ exchangers. Reproduced from Lipsius, S.L., Hüser, J. and Blatter, L.A. (2001) Intracellular Ca2+ release sparks atrial pacemaker activity. News Physiol. Sci. 16:101–106, with permission from the American Physiological Society; see Lipsius et al. 2001.