Endoplasmic Reticulum–Plasma Membrane Junctions as Sites of Depolarization-Induced Ca<sup>2+</sup>Signaling in Excitable Cells
Rose E. Dixon, James S. Trimmer
Abstract
Membrane contact sites between endoplasmic reticulum (ER) and plasma membrane (PM), or ER-PM junctions, are found in all eukaryotic cells. In excitable cells they play unique roles in organizing diverse forms of Ca 2+ signaling as triggered by membrane depolarization. ER-PM junctions underlie crucial physiological processes such as excitation-contraction coupling, smooth muscle contraction and relaxation, and various forms of activity-dependent signaling and plasticity in neurons. In many cases the structure and molecular composition of ER-PM junctions in excitable cells comprise important regulatory feedback loops linking depolarization-induced Ca 2+ signaling at these sites to the regulation of membrane potential. Here, we describe recent findings on physiological roles and molecular composition of native ER-PM junctions in excitable cells. We focus on recent studies that provide new insights into canonical forms of depolarization-induced Ca 2+ signaling occurring at junctional triads and dyads of striated muscle, as well as the diversity of ER-PM junctions in these cells and in smooth muscle and neurons.