The distribution of four lysosomal integral membrane proteins (LIMPs) in rat basophilic leukemia cells

The intracellular distribution of four distinct lysosomal integral membrane proteins (LIMPs), recognized by four monoclonal antibodies, was determined in rat basophilic leukemia (RBL) cells. The monoclonal antibodies were generated against hepatocyte LIMPs and have been characterized previously (Barriocanal et al., 1986a, b). Indirect immunofluorescence microscopy revealed that all four LIMPs are found in secretory vesicles of RBL cells. Ultrastructural immunolocalization, using a pre-embedding peroxidase technique, confirmed these results and also showed the distribution of LIMPs 1 and 4 at the cell surface. The relative, cell surface concentrations of the four LIMPs was determined using a fluorescence activated cell sorter (FACS). In resting RBL cells the concentration of LIMP 1 at the cell surface was highest, followed by LIMP 4. LIMPs 2 and 3 could not be detected at the cell surface. Following stimulation of secretory vesicle exocytosis by A23187, the cell surface concentration of LIMP 4 was increased, whereas the concentration of LIMPs 1-3 remained unchanged. These results are discussed within the context of intracellular sorting during the biogenesis of membrane, secretory vesicle components.