Receptor-mediated endocytosis of A14-125I-insulin by the nonfiltering perfused rat kidney.
The mechanism of insulin uptake and/or degradation in the peritubular circulation of the kidney was investigated using nonfiltering perfused rat kidneys, in which glomerular filtration was sufficiently reduced. After perfusion of A14-125I-insulin in the nonfiltering kidney for designated intervals, the acid-wash technique was employed to separately measure the acid-extractable and acid-resistant A14-125I-insulin, which were quantitated by HPLC and TCA-precipitability. HPLC profiles showed that the nonfiltering kidney metabolizes A14-125I-insulin only to a small extent during 1-h perfusion, suggesting that the peritubular clearance of A14-125I-insulin was not due to extracellular degradation but for the most part to uptake by the kidney. Acid-extractable A14-125I-insulin rapidly increased with time and reached pseudo-equilibrium with perfusate at approx. 10 min, whereas acid-resistant A14-125I-insulin increased continuously. An endocytosis inhibitor, phenylarsine oxide, inhibited significantly the acid-resistant A14-125I-insulin with no change in acid-extractable A14-125I-insulin, suggesting that the peritubular uptake of A14-125I-insulin largely represents endocytosis of the peptide into the intracellular space. Moreover, both the acid-extractable and acid-resistant A14-125I-insulin were significantly decreased in the presence of unlabeled insulin (1 microM). These lines of evidence suggest that insulin is taken up by the nonfiltering perfused kidney via receptor-mediated endocytosis (RME), which possibly occurs at the basolateral side of renal tubular cells, and that the peritubular clearance of insulin is largely accounted for by this mechanism.
Sato
H
H
Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
Yoshioka
K
K
Terasaki
T
T
Tsuji
A
A
D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004705:Endocytosis / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism*; D007444:Inulin / Q000378:metabolism; D007457:Iodine Radioisotopes; D007668:Kidney / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate / Q000502:physiology; D008954:Models, Biological; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000502:physiology*
D001152:Arsenicals; D007328:Insulin; D007457:Iodine Radioisotopes; C029341:oxophenylarsine; D007444:Inulin; D011972:Receptor, Insulin