Immunocytochemical localization on β-hexosaminidase and electron-microscopic characterization of human fibroblasts following treatment with monensin and nigericin

Immunocytochemical localization of beta-hexosaminidase in cultured human skin fibroblasts was performed in the presence or absence of the Na+/K+ ionophores monensin and nigericin. In the presence of monensin, beta-hexosaminidase accumulated in the periphery of swollen vesicles in the paranuclear region of fibroblasts from normal individuals and from patients with mucolipidosis II. Nigericin-treated cells had more extensive vacuolization of the cytoplasm and the localization of the enzyme was more diffuse within these vacuoles. Morphological studies at the ultrastructral level indicated that a perturbation of the Golgi region occurred during ionophore treatment. These findings suggest that beta-hexosaminidase in ionophore-treated fibroblasts is trapped in a time- and dose-dependent manner in the paranuclear region presumed to be the swollen cisternae of the Golgi region, or adjacent vesicles derived from the Golgi region. Furthermore, fibroblasts are more sensitive to perturbation by nigericin than by monensin at similar concentrations and exposure times. These data support biochemical findings that the two ionophores differentially inhibit the transport of lysosomal enzymes in the Golgi region.