Insulin binding, internalization, and degradation by a cultured kidney cell line
Yagil, C.; Ehmann, U.K.; Frank, B.H.; Rabkin, R.
American Journal of Physiology 254(5 Pt 1): E601-E608
1988
ISSN/ISBN: 0002-9513 PMID: 2834959 Document Number: 313192
Proximal tubules are a key site of insulin metabolism, which is in part a receptor-mediated process. To explore the interaction between insulin and the kidney and to evaluate the role of receptors in insulin uptake and processing, a study was carried out with a cultured proximal-like opossum kidney (OK) cell line. 125I-insulin associated with confluent monolayers in a specific manner, and this interaction was competitively inhibited by insulin; unrelated peptides were relatively ineffective. Insulin degradation exhibited time and temperature dependency and up to a concentration of 5 .times. 10-8 M was not saturable. Degradation exhibited partial hormone specificity. Separation of plasma membrane bound from internalized insulin was achieved by lowering extracellular pH. At 4.degree.C, 94% of cell-associated radioactivity was membrane bound, whereas at 37.degree.C, in the steady state, 33% was membrane bound and 67% was internalized. There was a significant corelation between membrane-bound insulin and the rate of degradation. These findings reveal that the binding and processing of insulin by the kidney cell line are compatible with the description f the uptake of filtered insulin by the proximal tubule in the intact kidney. Accordingly we conclude that this cell line provides a good model for studying renal epithelial uptake and metabolism of insulin.