Intratubular microinjection study of gentamicin transport in the rat

The intratubular microinjection technique was used to determine the absorptive flux of radioactive gentamicin the rat. Microinjection into the early tubule and late proximal tubule resulted in recoveries of proximal 66.6 +/- 3.6% and 80.4 +/- 3.4%, respectively. Recoveries after microinjection into the distal convoluted tubule averaged 101.0 +/- 4.3%. The addition of tobramycin, phospholipase A, spermine or probenecid to the microinjection solution inhibited gentamicin absorption. These studies indicate that an absorptive flux of gentamicin is present in the superficial proximal tubule and at a nephron site or sites between the superficial proximal and distal tubules. Gentamicin absorption is mediated by a phospholipid carrier with specificity for polyamines and other aminoglycosides. The presence of probenecid in the perfusion solution inhibited the tubular absorption of gentamicin.