BIOCHEMICAL, HISTOCHEMICAL AND ELECTRON-MICROSCOPIC STUDIES OF 5-HYDROXYTRYPTAMINE IN NEOPLASTIC MAST CELLS

¹ Departments of Pharmacology and Pathology, Yale University School of Medicine, New Haven, Connecticut

Neoplastic mast cells maintained in cell culture have been examined by biochemical, microfluorometric histochemical and electron-microscopic methods, in an investigation of the storage and disposition of endogenous and exogenous 5-hydroxytryptamine (5-HT). Endogenous 5-HT was found to be stored within multivesicular bodies which contained two hydrolytic enzymes (acid phosphatase and thiolacetic esterase) generally found associated with lysosomes. Treatment of neoplastic mast cells with reserpine (10^-7 M) produced a loss of 5-HT from most cells and a decrease in the number of multivesicular bodies. A clone of cells containing very low levels of endogenous 5-HT took up 5-HT from the culture medium, with the appearance of fluorescent cytoplasmic bodies on fluorescence histochemical examination, and increased electron-opacity of the multivesicular bodies seen by electron microscopy. Reserpine inhibited both morphologic changes, and in reserpine-treated cells a halo of 5-HT fluorescence was noted at the cytoplasmic membrane. The nature of amine storage bodies in these cells is discussed and the possibility of multiple sites of action of reserpine is indicated.