Transport of gentamicin and fluid-phase endocytosis markers in the LLC-PK1 kidney epithelial cell line.

In order to characterize the transport of aminoglycoside in the cultured kidney epithelial cell line LLC-PK1, cellular uptake of gentamicin was studied in comparison with those of fluid-phase endocytosis markers, lucifer yellow and horseradish peroxidase. The uptake of gentamicin and fluid-phase markers were time-dependent and were reduced at low temperature. The rate of gentamicin uptake was, however, faster than those of lucifer yellow and horseradish peroxidase, and was saturable. The accumulation of gentamicin in the cells was increasing even after 6 days of incubation, whereas that of lucifer yellow reached a steady state by 1 day. Release of intracellular gentamicin from LLC-PK1 cells was much slower than that of lucifer yellow. Gentamicin uptake, but not lucifer yellow uptake, was increased by reducing the ambient ionic strength. Under the low ionic strength conditions, gentamicin uptake was inhibited by the presence of other aminoglycosides, lysozyme, polyamines such as spermine and inorganic cations such as calcium. These results indicate that gentamicin electrostatically binds to the cell apical membrane and is subsequently taken up by an adsorptive endocytosis in LLC-PK1 cells.