An immunocytochemical and in situ hybridization analysis of annexin 1 expression in rat mast cells: modulation by inflammation and dexamethasone.

The presence and localization of the anti-inflammatory protein annexin 1 (also known as lipocortin 1) in perivenular rat mast cells was investigated here. Using the rat mesenteric microvascular bed and a combination of morphologic techniques ranging from immunofluorescence to electron microscopy analyses, we detected the presence of annexin 1 in discrete intracellular sites, both in the nucleus and in the cytoplasm. In resting mast cells, most of the protein pool (approximately 80% of the cytosolic portion) was localized to cytoplasmic granules. In agreement with other cell types, treatment of rats with dexamethasone (0.2 mg/kg, ip) increased annexin 1 expression in mast cells, inducing a remarkable appearance of clusters of protein immunoreactivity. This effect was most likely the result of de novo protein synthesis as determined by an increase in mRNA seen by in situ hybridization. Triggering an ongoing experimental inflammatory response (0.3 mg of carrageenin, ip) increased annexin 1 mRNA and protein levels. In conclusion, we report for the first time the localization of annexin 1 in connective tissue mast cells, and its susceptibility not only to glucocorticoid hormone treatment, but also to an experimental acute inflammatory response.

Demonstration of mitochondrial mineral deposits in osteoblasts after anhydrous fixation and processing.

The fine structure of early developing bone was examined using a modification of a new non-aqueous processing method in which anhydrous glutaraldehyde dissolved in dimethylsulphoxide (GLUT-DMSO) is used as a fixative. Preliminary results show that the basic morphological features of the cellular and extracellular compartments of developing bone were preserved. The cytoplasm of osteoblasts revealed numerous well-preserved mitochondria and other membranous organelles. Inside the mitochondria there were large and conspicuous electron-opaque granules of mineral which were more prominent and numerous than in specimens prepared by conventional aqueous procedures. The collagenous matrix also revealed electron-opaque deposits of mineral. These results support the evidence for the existence of mitochondrial calcium phosphate in osteoblasts in the form of granules.