Special relationship between mitochondria and hypolemmal nerve terminals in salivary glands of some bats.

Background: Hypolemmal nerve terminals, which are abundant in many types of salivary glands, are naked axons that have penetrated the basement membrane to take up a position between adjacent parenchymal cells. Although they may form vesicle-filled varicosities, there usually are no obvious morphological indications as to which cell actually is being innervated.
Methods: Specimens of over 200 species of bats were live-trapped and their major salivary glands extirpated and prepared for electron microscopic examination.
Results: In 13 species of bats out of the more than 200, mitochondria-hypolemmal nerve terminal complexes were observed in different sites in different salivary glands. In these 13 species, mitochondria in epithelial cells that abut nerve varicosities are closely applied to the plasma membranes of their cells to follow the contours of these nerve elements. The complexes so formed often consist of a varicosity flanked by two mitochondria in separate cells. In intensely innervated glandular segments, mitochondria may be opposed not only to varicosities, but to the axonal portions of these nervous elements as well.
Conclusions: The physiological significance of such complexes is unknown; it is conceivable that the mitochondria facilitate signal transmission or play a role in local calcium homeostasis related to nerve function.