Electron microscopy of watery vacuole formation in rat parotid acinar cells during reflex stimulation

Reflex stimulation from eating hard chow caused variable degrees of watery vacuolation, most conspicuously in animals that had eaten the most food; this was accentuated by eating in the cold. Some vacuolation occurred in the absence of sympathetic impulses but there was much more in glands receiving both parasympathetic and sympathetic impulses. Vacuole formation was often associated with, but not dependent upon, a degree of acinar degranulation. The vacuoles appeared to originate either from the inner side of the Golgi apparatus, near condensing vacuoles, or from ballooning within the rough endoplasmic reticulum; some vacuoles appeared to arise close to secretory granules. Certain cellular components, including secretory granules, entered the contents of vacuoles, which also often had connections with lumina. Many basally-located vacuoles were large and bounded only by a tenuous layer of cytoplasm which was contained by the basal lamina. Vacuole formation may be related to strong stimulation of susceptible cells, which occurs to a variable extent during natural reflex secretion, as well as during artificial stimulation. Thus, under normal conditions, certain macromolecular components might enter saliva via this route and not solely by exocytosis. Leakages from acinar vacuoles could also occur into the glandular interstices, accounting for some of the parotid amylase found in peripheral blood.