Abstract
Subsurface cistern (SSC) in neuronal soma and primary dendrites is a specialized compartment of endoplasmic reticulum (ER) that is in close apposition (10 nm) with the plasma membrane (PM). ER-PM contact areas are thought to be involved in intracellular calcium regulation. Here, structural changes of SSC in hippocampal neurons were examined by electron microscopy upon depolarization with high K+ (90 mM) or application of NMDA (50 μM) in rat dissociated cultures as well as organotypic slice cultures. The number and average length of SSC-PM contact areas in neuronal somas significantly decreased within 30 s under excitatory condition. This decrease in SSC-PM contact area progressed with time and was reversible. These results demonstrate a structural decoupling between the SSC and the PM upon stimulation, suggesting that there may be a functional decoupling of the calcium regulation. Because SSC-PM contact areas may mediate calcium influx, the decrease in contact area may protect neurons from calcium overload upon heightened stimulation.
Highlights
Specialized contact areas between endoplasmic reticulum (ER) and plasma membrane (PM) are termed as ER-PM connections, contact sites, or junctions, which have welldefined structural characteristics and are involved in calcium regulation and lipid transport [1, 2]
The length of SSC is the linear measurement of the PM-SSC contact area where the two membranes are rigidly apposed (e. g., the edges of Ultrastructure of subsurface cisterns (SSCs) SSC in neurons is composed of an ER stack closely apposed to the plasma membrane
The SSC-PM contact area significantly decreased upon excitatory stimulation in dissociated rat hippocampal neuronal cultures One striking observation is that the SSC-PM contact area in neuronal somas conspicuously decreased upon depolarization with high K+ (Fig. 3)
Summary
Specialized contact areas between endoplasmic reticulum (ER) and plasma membrane (PM) are termed as ER-PM connections, contact sites, or junctions, which have welldefined structural characteristics and are involved in calcium regulation and lipid transport [1, 2]. One of the most studied functions of ER-PM contact areas is storeoperated calcium entry (SOCE), a fundamental signaling mechanism in majority of cell types including neurons [3, 4]. Store depletion induces increased formation of ER-PM contact areas, and this dynamic process is often visualized by live observation of overexpressed STIM1 (stromal interaction molecule 1), an ER protein closely involved in SOCE [5]. ER-PM contact can be induced by different mechanisms as well as by overexpression of different proteins in many cell types. Few such studies [3, 8] were carried out in neurons
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