Formation of endoplasmic reticulum networks in vitro

In vitro endoplasmic reticulum (ER) networks provide an accessible ER preparation, which can be utilized to study a variety of ER functions. As they are stabilized on a cover slip, they can be microscopically visualized even while the buffer is being exchanged. Biochemical amounts of network can be prepared for study by preparing networks that cover areas as large as 1 cm² on a single cover slip. There is considerable interest in the regional specialization of the ER. The dimensional similarity between the in vitro networks and in vivo ER networks supports the notion of functional similarity. This opens the possibility of studying ERs from many other systems, including the sarcoplasmic reticulum from muscle. There are many concerns about the dynamics of Ca²⁺ movement in the cytoplasm, which are thought to be controlled by the ER. Absolute levels of Ca²⁺ are difficult to measure because of the small luminal volume and only relative changes in Ca²⁺ concentration have been measured to date. Still, there are many issues that can be addressed. They provide a useful alternative to in vivo studies of ER functions because of the relative ease with which the networks can be produced. There are potential difficulties resulting from the loss of components in preparation of the components for reconstitution. This, however, can be an advantage if the lost components and lost activities can be recovered with other fractions.