The clonal smooth muscle cell line A10, derived from fetal rat aorta, binds 125I-insulin-like growth factor I at a Type 1 insulin-like growth factor receptor. Threonine-59 insulin-like growth factor I, multiplication stimulating activity, and insulin inhibit the binding with IC50 = 10 nM, 84 nM, and 500 nM, respectively. Insulin in high concentrations (greater than 5 microM) completely inhibits...