V/V0 is denoted by ○, and the frequency of exocytotic events is denoted by •. A, Ca2+-free solution evoked shrinkage in unstimulated antral mucous cells. Subsequent ACh stimulation evoked transient cell shrinkage, but did not activate exocytotic events (n = 6). B, Ni2+ also evoked cell shrinkage in unstimulated antral mucous cells. ACh stimulation subsequent to the addition of Ni2+ evoked both exocytotic events and cell shrinkage (n = 4). However, both the frequency of exocytotic events and the extent of cell shrinkage were reduced compared with those in control experiments.