Biochemical mechanisms of aminoglycoside cell toxicity. I. The uptake of gentamicin by cultured skin fibroblasts and the alteration of lysosomal enzyme activities.

In order to study the toxicity of aminoglycoside, human skin fibroblasts were used as a model for basic studies, since they are known to have a specific aminoglycoside-binding site and to translocate the drug into the cells. Following the exposure of fibroblasts to gentamicin for 3 days, the cells formed many osmiophilic lamellar materials (myeloid bodies) in the lysosomes, while the other cellular structures appeared to remain normal. Although gentamicin was intensively accumulated within the lysosomes, intralysosomal pH, determined by the fluorescence intensity ratio method using fluorescein-isothiocyanate-labeled dextran, did not alter. Among the lysosomal enzymes, the activities of six different glycosidases were unchanged. On the other hand, sphingomyelinase and acid lipase activities were greatly decreased, while phospholipase A activity was increased. These results indicate that the lipid metabolism of fibroblasts is altered by gentamicin treatment, and that perturbation of intralysosomal pH can not be the cause of the changes observed in cell lysosomal enzyme activities.