Decreased Cellular Toxicity of Neomycin in a Clonal Cell Line Isolated from LLC-PK1

We have previously shown in LLC-PK1 cells, that apical membrane enzyme activity was inhibited by aminoglycoside antibiotics (Am. J. Physiol. 254, C251-C257, 1988). In the present study, the relationship between the lethal cytotoxic effect of aminoglycoside and its effect on apical membrane enzyme was examined by establishing aminoglycoside resistant cells. A clonal cell line, LLC-PK1/NRa3, was isolated from parent LLC-PK1 cells in the presence of neomycin. Neomycin inhibited colony formation and increased the number of floating dead cells in parent LLC-PK1 cultures. In contrast, these cytotoxic effects of neomycin were negligible or less pronounced in NRa3 cells, indicating that NRa3 cells were more resistant to neomycin compared with the parent cells. The inhibitory effect of neomycin on apical enzyme activity was significantly weaker in NRa3 cells than in the parent cells. These results suggest that a common mechanism is involved in the aminoglycoside-induced reductions in the apical enzyme activity and in cell viability of LLC-PK1 cells.