Two types of exocytosis evoked by ACh in salivary acinar cells: a morphological observation in perfused submandibular gland of rats.

Exocytosis in the perfused rat submandibular gland was studied using electron microscopy. Stimulation with 1 microM acetylcholine (ACh) evoked exocytosis; i.e., the secretory granules fused with the luminal membrane and their contents were extruded into the luminal space, and watery vacuoles were observed in some acinar cells. Stimulation with 1 mM ACh also induced exocytosis, and led to a marked increase in the number of watery vacuoles. Some watery vacuoles were connected to the lumen and were thus suggested to be formed by the fusion of the granules. On the other hand, no watery vacuoles were observed in the acinar cells during 1 microM isoproterenol stimulation, while isoproterenol induced exocytosis and led to a marked decrease in the number of intracellular granules. Thus, the watery vacuolation is a characteristic response to the cholinergic stimulation, is dependent on the ACh dose in the submandibular acinar cells, and is regarded as a kind of exocytosis.