Multitubular bodies in intestinal cells of Amphiuma means/tridactylum (Urodela): ultrastructural characterization.

The jejunal absorptive cells of the salamander Amphiuma, when examined using transmission electron microscopy, were found to possess a unique type of intracellular vacuole containing membranous tubules. These vacuoles, tentatively named multitubular bodies, were located in the cytoplasm between the nucleus and the brush-border membrane, and were seen with greatest frequency in the summer and fall. The vacuoles containing multitubular bodies had an average diameter of 0.6 microns, and the membranous tubules within had an average diameter of 30 nm. The tubules differed morphologically from the vesicles in the multivesicular bodies, and from the primary lysosomes in the polylysosomal vacuoles. The tubules did not exhibit acid phosphatase activity, and were of similar diameter and membrane thickness as the Golgi saccules. In contrast to the multivesicular bodies, the multitubular bodies did not take up exogenous horseradish peroxidase. Early forms of autophagosomes resembling these vacuoles were often seen in the para-Golgi region of the cell. The multitubular bodies may represent a distinct type of autophagosome. Although the exact origin of the tubules as well as their role in cellular activity is unclear, their seasonal appearance within the multitubular bodies of the absorptive cells suggests a unique means of selective down-regulation of Golgi-like organelles.