DOSE EFFECTS OF ACETYLCHOLINE ON THE CELL-VOLUME OF RAT MANDIBULAR SALIVARY ACINI

The effects of acetylcholine (ACh) on the cell volume of the isolated rat mandibular acini were studied stereologically using video-enhanced contrast optical microscopy. The lengths of major and minor axes of the acini were measured in the successive video images, from which the relative volume change was estimated. ACh induced a rapid shrinkage of the acinar cell to reach minimum volume within 1 min. Simultaneously, the acinus and acinar clump shrunk in the same proportion as the acinar cell. The initial volume decrease induced by ACh was dose dependent: 0.92 at 10(-8) M, 0.91 at 10(-6) M, 0.77 at 10(-5) M, 0.78 at 10(-4) M, and 0.75 at 10(-3) M (the relative volume compared with the resting control). During sustained stimulation by ACh for 3 min, the volume of acinar cell remained at the plateau level at concentrations lower than 10(-5) M ACh, whereas the volume increased by 0.1-0.15 at concentrations higher than 10(-4) M ACh. The dose-dependent manner of the cell volume coincided with the fluid secretion measured in the isolated perfused gland. The findings on the dose effects of ACh are discussed in connection with the intercellular communication and the movement of electrolytes.