Nerve growth factor binding sites on hepatic parenchymal cells.

Nerve growth factor (NGF) binding sites on rat hepatocytes (HCs) in culture for 24 to 48 h were characterized using 125I-NGF. Specific binding of 125I-NGF to HCs was saturable. Scatchard analysis indicated a single population of binding sites with a Kd of 5.5 nM and a Bmax of 540 fmol/mg protein. In isolated hepatocyte membranes, specific binding of 125I-NGF was also apparent with Kd and Bmax values of 10.8 nM and 3740 fmol/mg protein, respectively. Specific binding of 125I-NGF to HCs was displaced by excess, unlabeled NGF but not by up to 1000-fold excess of either insulin or epidermal growth factor. Internalization/sequestration of 125I-NGF into HCs was measured as radioactivity present in solubilized cells after exposure to high salt and acid. These studies indicated 83 +/- 11% of 125I-NGF was accumulated by internalization/sequestration at a concentration of 1 nM 125I-NGF. Internalization was reduced to 43 +/- 4% when incubations were carried out at 4 degrees C. These results indicate the presence of a specific, low-affinity binding site for NGF on hepatocytes in culture.