cisternae

Cisternae are flattened, membrane-bound sacs that form a common structural unit in several organelles of eukaryotic cells. They consist of a phospholipid bilayer enclosing a continuous lumen and are interconnected by tubules and vesicular transport. The term cisterna (plural cisternae) is used to describe these sacs in particular organelles such as the endoplasmic reticulum and the Golgi apparatus.

In the endoplasmic reticulum, cisternae create a network that extends throughout the cytoplasm. The rough endoplasmic reticulum contains ribosome-studded cisternae, whereas the smooth endoplasmic reticulum lacks ribosomes. The ER lumen is connected to the perinuclear space. Rough ER cisternae synthesize and fold membrane and secreted proteins; rough ER also initiates post-translational modifications. Smooth ER cisternae synthesize lipids, metabolize carbohydrates, and detoxify certain substances; in muscle cells, an ER-derived network called the sarcoplasmic reticulum stores and releases calcium.

Within the Golgi apparatus, cisternae are arranged in stacked, flattened sacs organized into cis, medial, and trans regions. Cargo arrives at the cis face in vesicles from the ER; successive cisternae modify cargo through glycosylation, sulfation, and processing enzymes; final products exit from the trans face in vesicles to lysosomes, the plasma membrane, or secretory pathways. There are two main models of Golgi transport: the vesicular transport model, where vesicles ferry cargo between static cisternae; and the cisternal maturation model, where cisternae themselves mature and move cargo forward, with retrograde vesicles recycling enzymes.

Because cisternae are a general term for membrane-bound sacs, the concept also appears in other organelles and tissues and varies in size and composition between cell types. Electron microscopy is typically used to study cisternal structure.