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We used ultrastructural autoradiographic and cytochemical methods to localize esterase activities in unstimulated guinea pig basophils and in basophils undergoing degranulation or recovery from degranulation. We used tritium-labeled diisopropylfluorophosphate (DFP) as a probe for serine enzymes and localized this probe by ultrastructural autoradiography to cytoplasmic granules of immature or mature unstimulated basophils, as well as to granules released by degranulating basophils. Ultrastructural cytochemistry using alpha naphthyl acetate (ANA) as substrate localized nonspecific esterase activity to extruded granules, either within the interiors of degranulation sacs or within granules completely separated from degranulating basophils. Extruded granules retained their esterase activity for as long as 24 hr after antigen-induced degranulation. The plasma membranes of unstimulated or degranulating basophils, as well as of basophils recovering from degranulation, displayed prominent cell surface ANA esterase ectoenzyme activity. Lipid bodies, organelles present in the cytoplasm of both control and recovering basophils, were also alpha naphthyl acetate esterase (ANAE)-positive. Thus, cytochemical and autoradiographic techniques localized esterase and/or [3H]-DFP-binding activities to cytoplasmic granules, lipid bodies, and cell surface of basophils, and these enzyme activities persisted during both degranulation and recovery from degranulation.

We studied the localization of nonspecific esterase activities in cloned guinea pig aortic endothelial cells using ultrastructural cytochemistry. Weibel-Palade bodies (WPB), which are known to contain von Willebrand protein, were positive for esterase, defining a heretofore unrecognized activity of these organelles. Esterase activity was also found localized to the external surface of the plasma membrane, to cytoplasmic lipid bodies, and to the outer (cytoplasm-facing) surface of certain membrane-bound cytoplasmic vacuoles. Localization of esterase activity to these four discrete sites probably reflects the presence of a number of endothelial cell enzymes capable of hydrolyzing alpha-naphthyl acetate or butyrate. The physiological substrate and biological function of these enzyme activities are not presently understood.