Distinct receptors for insulin-like growth factor I in rat renal glomeruli and tubules

Academic Article

Abstract

  • Purified preparations of renal glomeruli and tubules were obtained by a procedure involving perfusion of rat kidneys with magnetic iron oxide particles to selectively separate the iron-containing glomeruli from the nonmagnetic tubules. Detergent-soluble extracts of both renal glomerular and tubular membranes showed high-affinity, specific binding of 125I-labeled insulin-like growth factor I (125I-IGF-I), whereas degradation of this peptide hormone was minimal during a 90-min incubation at 22°C in the presence of 2.5 mM EDTA and 5 mM N-ethylmaleimide. The affinity of these receptors for IGF-I appeared identical in the two types of renal tissue, since 50% inhibition of 125I-IGF-I binding to both glomerular and tubular tissue occurred in the presence of ~3 x 10-9 M unlabeled IGF-I. In contrast, insulin was much less effective at blocking 125I-IGF-I binding to either tissue, with 1 x 10-6 M insulin required to produce 50% inhibition of binding. Relative to 125I-IGF-I binding, 125I-insulin binding to glomerular and tubular tissue was significantly lower per milligram protein. 125I-IGF-I was specifically cross-linked to a glomerular receptor subunit that migrated as two discrete bands with relative molecular weight (M(r)) of 140,000-150,000 on sodium dodecyl sulfate polyacrylamide gels in the presence of 40 mM dithiothreitol. In contrast, 125I-IGF-I was cross-linked to a tubular receptor subunit that migrated as two discrete bands but at a slightly different position, with M(r) of 120,000-140,000. Cross-linking studies with 125I-insulin yielded a single band on sodium dodecyl sulfate polyacrylamide gels, M(r) 130,000, in both renal glomeruli and tubules. These results provide evidence for the existence of distinctive high-affinity receptors for IGF-I in both glomeruli and tubules.
  • Published In

    Author List

  • Pillion DJ; Haskell JF; Meezan E
  • Volume

  • 255
  • Issue

  • 4