title: Characterization of insulin-like growth factor I receptor on human erythrocytes.
abstract: [125I]Insulin-like growth factor I (IGF-I) specifically bound to erythrocytes; the binding was saturable, and time and temperature dependent. Steady state binding was reached at 16 h at 4 C, and specific binding averaged 14.3 +/- 0.7% (+/- SEM) at a concentration of 3.6 X 10(9) cells/ml in seven normal subjects. [125I]IGF-I binding to the cells was displaced by unlabeled IGF-I in a dose-dependent manner. Scatchard analysis indicated a linear plot, and Ka and number of binding sites/cell were 1.43 +/- 0.07 X 10(9) M-1 and 20.7 +/- 2.2, respectively. Compared to IGF-I, the relative potencies of multiplication-stimulating activity and insulin for displacing [125I]IGF-I binding were 20% and 1%, respectively. [125I]IGF-I binding to erythrocytes from patients with acromegaly was lower than binding to cells from pituitary dwarfs. An inverse correlation between plasma IGF-I level and the number of IGF-I-binding sites per cell was found (r = -0.75; P less than 0.005). These results demonstrate that [125I]IGF-I binding to erythrocytes can be used for clinical measurement of the IGF-I receptor.
mesh_terms: D000172:Acromegaly / Q000097:blood; D000293:Adolescent; D000328:Adult; D001667:Binding, Competitive; D004393:Dwarfism, Pituitary / Q000097:blood; D004912:Erythrocytes / Q000378:metabolism*; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000097:blood*; D013696:Temperature
chemical_list: D007328:Insulin; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I