Morphometric analysis of mucous granule depletion and replenishment in rat colon

Computer-assisted morphometric analysis was used to quantify mucous granule discharge and the subsequent replenishment of secretory granules in the rat colon following cholinergic challenge. Within 5 min of stimulation (250 micrograms/kg carbachol, subcutaneous), the volume of intracellular mucous granules decreased to 61.5% of the control. The apical plasma membranes of goblet cells in the midcrypt region became deeply cavitated, indicating that they had accelerated mucous granule secretion by a process of compound exocytosis. Goblet cells at the base of the crypt rarely showed cavitated apical membranes but clearly became depleted of intracellular mucous granules. At 60 min after stimulation, cavitated profiles were very rare (< or = 0.4%) but intracellular stores of mucous granules were still significantly depressed (54.7% of control). By 4 hr after stimulation, mucous granule stores recovered to 94.9% of control levels. Morphometric quantification was found to be a reliable and sensitive measure of recent goblet cell secretory activity.