Endocytosis and Exocytosis in Rabbit Lacrimal Gland Acinar Cells

Abstract

The main function of the lacrimal gland is to maintain the surface of the eye moist, well lubricated, and free of irritants. It achieves this function by secreting ions, proteins, and water. Recent studies have shown that stimulation of lacrimal cells by carbachol, an acetylcholine analogue, not only triggers release of secretory products across the apical plasma membrane and activates various ion transporters involved in the trans-epithelial secretion of Na⁺ and Cl⁻, but it also causes Na⁺, K⁺-ATPase pump units to be mobilized from a cytoplasmic pool and inserted into the baso-lateral plasma membrane (Yiu et al., 1988). Recent studies suggest that carbachol also increases the rate of endocytosis at the baso-lateral surface (Lambert et al., 1993). We have analyzed the internalization and release of a fluorescent fluid phase marker, Lucifer Yellow, in order to learn more about the control of membrane trafficking in acinar cells from rabbit lacrimal glands and to discern the roles of distinct intracellular compartments. In an attempt to evaluate the extent to which fluid phase marker internalization reflects the retrieval of secretory vesicle membranes, we have also measured protein secretion.