INTERCELLULAR MATERIAL IN THE BASAL AND LATERAL FOLDS OF PAROTID SEROUS CELLS IN 4 SPECIES OF BATS

Background: Basal folds are slender plications at the basal surface of acinar cells in the salivary glands of many mammalian species. These largely organelle-free folds increase the surface area of the basal pl asmalemma manyfold and are unquestionably involved in the translocatio n of organic and inorganic molecules and water into the acinar cells. Methods: Specimens of salivary glands were obtained from over 230 spec ies of live-trapped bats fi om major areas of the globe. Tissues for e lectron microscopy were fixed and processed by conventional means. Res ults: A number of the bat species examined had dense material in the i ntercellular spaces between basal and lateral folds of serous cells in the parotid gland. This intercellular material was particularly promi nent in three species of New World bats, viz., Pteronotus parnellii, P . quadridens, and Phyllostomus latifolius, and in one species of Old W orld bats, Chalinolobus argentatus. This dense material, which has a f arinaceous texture, appears not to pass through tight junctions, so it is excluded from the lumina of intercellular canaliculi and acini. Th e dense material originates in the acinar cells-it is carried to the m embranes of the folds via coated vesicles, which empty their dense con tent by exocytosis into the intercellular space. Similar dense materia l is present in the intercellular spaces of the basal labyrinth of str iated ducts in the two species of Pteronotus. The manner in which this material accumulates in the striated duct is unclear. Conclusions: Al though the function of the intracellular dense material is undetermine d, it appears to be placed strategically to influence molecular traffi c into acinar cells or to modulate the paracellular pathway. From a co mparative evolutionary perspective, we hypothesize that, in bats, the combination of basal folds and extracellular densities is associated w ith insectivory. Similar morphologies appear to be lacking in frugivor ous or nectarivorous species. (C) 1998 Wiley-Liss, Inc.