Abstract
In confirmation of previous reports, the thiolacetic acid technique represents a simple and reliable method for the demonstration of motor endplates in striated muscles. This type of esterase is present in many other locations as well. When its distribution pattern was compared with that for nonspecific esterase, it was found to be identical, although in some locations nonspecific esterase was active in additional sites. The effect of various inhibitors on the staining reaction, which was carried out in most instances in sections fixed in chilled Baker's CaCl2 formalin, was also quite similar. A notable exception, however, was observed in the pancreas of various species. In contrast to the marked activity of nonspecific esterase in the acinar cells, no staining was noticed in sections incubated in the thiolacetic acid medium. However, addition of sodium taurocholate converted this negative reaction into a strong positive one, indicating that under this circumstance a true lipase was visualized. Following the treatment of sections from rat kidney and liver with organophosphorous compounds, particularly E 600 (diethyl-p-nitrophenylphosphate), cytoplasmic activity was suppressed and staining in droplets became very noticeable in sections prepared for the demonstration of both nonspecific and thiolacetic esterase. Thus, these structures at present identified with de Duve's lysosomes contained a different kind of esterase (C esterase of Pearse with a cathepsin-like activity). The implications of these findings are discussed in reference to the significance of the intercellular localization of esterase and the differentiation of various esterases on the basis of organophosphorous inhibitors. It is concluded that thiolacetic acid esterase under histochemical conditions is hydrolyzed by acetylcholinesterase at least in the motor endplates, by B or aliesterase in the cytoplasm, and by type C esterase in the lysosomes and under appropriate circumstances also by pancreatic lipase.