Similarity of junctions between plasma membranes and endoplasmic reticulum in muscle and neurons.

TLDR

Freeze‑fracture microscopy was used to examine the membrane architecture at junctions between the plasma membrane and underlying endoplasmic reticulum cisterns in amphioxus muscle and mouse cerebellar neurons. The study revealed that subsurface cisterns in amphioxus muscle and mouse cerebellar neurons form junctions with the plasma membrane, characterized by large particle aggregates on the protoplasmic leaflet and complementary pits on the external membrane, indicating a shared specialization that likely couples intracellular activity to membrane electrical activity.

Abstract

The structure of membranes at junctions between the plasma membrane and underlying cisterns of endoplasmic reticulum in amphioxus muscle and mouse cerebellar neurons was studied using the freeze-fracture technique. In amphioxus muscle, subsurface cisterns of sarcoplasmic reticulum form junctions with the surface membrane at the level of the sarcomere I bands. On the protoplasmic leaflet of the sarcolemma overlying these junctions were aggregates of large particles. On the protoplasmic leaflet of the membranes of cerebellar basket, stellate and Purkinie cells there were similar aggregates of large particles. In both tissues, the corresponding external membrane halves had arrays of pits apparently complementary to the aggregates of large particles. Cross fractures through junctions showed that the particle aggregates in neuronal and muscle membranes were consistently located over intracellular cisterns closely applied to the plasma membrane. Thus, a similar plasma membrane specialization is found at subsurface cisterns in mammalian neurons and amphioxus muscle. This similarity supports the hypothesis that subsurface cisterns in neurons, like those in muscle, couple some intracellular activity to the electrical activity of the plasma membrane.