Intracellular enzyme localization in the epithelium of the bovine glandular stomach

The intracellular localization of calcium adenosine triphosphatase (Ca2(+)-ATPase) was studied ultracytochemically in the pyloric glands of the abomasal mucosa of cattle. A remarkable staining pattern exhibited the Golgi apparatus, as there was a gradation in staining of the interior sides of dictyosomal cisternae from the not or weakly stained cis to the heavily stained trans face. Membranes of Golgi-endoplasmic reticulum lysosome complex-secretory vesicles showed either no or strong enzyme activity. Membranes of secretory vesicles accumulated in the cell apex stained positive for ATPase activity. This accounts also for the apical cortical cytoplasm. From these results it is speculated that Ca2(+)-ATPase may play an important role in the pathway of exocytotic secretion, especially in the process of membrane sorting and biogenesis of secretory vesicles, in the steps of vesicle accumulation and transport to the site of exocytosis as well as in membrane fusion events.