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Intracellular accumulation of a fluorescent derivative of paromomycin in human fibroblasts

Human fetal lung fibroblasts grown in the presence of dansyl‐paromomycin (DNS‐Pm), a fluorescent derivative of the aminoglycoside antibiotic, paromomycin, probably accumulate DNS‐Pm in the lysosomes. The intracellular concentration of DNS‐Pm is proportional to the extracellular concentration and to the length of time cells are exposed to the compound. The accumulation of DNS‐Pm by human fibroblasts continued to increase for several days, reaching a saturation after 7 days. The kinetic data are consistent with the establishment of a steady state in the cell between fluid‐phase pinocytosis and exocytosis of DNS‐Pm. About 80% of the intracellular DNS‐Pm was released in 24 hr when fresh medium without the analogue was added. The residual 20% remained within the cells, suggesting that it may be irreversibly bound to the lysosomes, endoplasmic reticulum, or ribosonius. The uptake of paromomycin by cells in culture may be a useful means to study error propagation during growth and lifespan of cells in vitro.