Ultrastructural localization of secretory glycoconjugates in the gallbladder epithelium of the Richardson’s ground squirrel before and during cholesterol gallstone formation

Hypersecretion of mucin is a critical feature of gallbladder epithelial cells in ground squirrels fed a 2% cholesterol-enriched diet for the induction of cholesterol gallstone formation. The timing of this physiological response indicates a potential role for mucin as an initiator of cholesterol crystal nucleation from supersaturated bile. There is little information regarding the specific type of glycoprotein secreted by gallbladder epithelia and routine light microscope histochemistry proved unproductive for detection of specific glycoprotein types being synthesized as the intracellular accumulations were not large enough to permit visualization of a colored precipitate. Ultrastructural histochemistry was utilized to differentiate between the two main mucin types secreted by the gastrointestinal tract - sulphated and sialomucins.Two ultrastructural methods utilizing the histochemical basis of the high and low iron diamine techniques were used. The high iron diamine (HID) technique imparts density to sulphated complex carbohydrates while the low iron diamine (LID) method imparts density to acidic glycoconjugates.