Autoradiography of gentamicin uptake by the rat proximal tubule cell

Rats were injected with 25 microCi (14.2 microgram) of tritiated gentamicin and were killed 10 min, 1 hour, or 24 hours after the injection. Renal tissue was preserved by intravascular perfusion of a glutaraldehyde-containing solution. In a preliminary experiment, glutaraldehyde was found to fix gentamicin to bovine serum albumin, and this property probably accounted for the negligible loss of label during specimen preparation. By light microscopy, gentamicin appeared to be confined almost entirely to the proximal tubules. Autoradiographic grains appeared initially over the apical cytoplasm of the proximal tubule cells and, with time, moved progressively into the interior of the cell. Electron-microscopy revealed that the grains were associated with apical vesicles at 10 min and lysosomes at 1 and 24 hours. The specificity of labeling was confirmed by quantitative grain analysis. These results indicate that gentamicin is transported into the proximal tubule cell by pinocytosis and becomes sequestered in lysosomes. This process may account for the accumulation of myeloid bodies in the proximal tubule lysosomes of gentamicin-treated rats, but whether this mechanism contributes the nephrotoxicity of this drug cannot be ascertained at this time.