AbstractRecombinant rat CNTF (ciliary neurotrophic factor) at picomolar concentration prevents the death of P19 murine embryonic carcinoma cells that usually follows upon withdrawal of serum from the culture medium. For prolonged survival of P19 cells in serum‐free medium, insulin must also be present. In the presence or absence of serum, CNTF stimulates the differentiation of P19 cells, inducing the formation of neurites and synthesis of neurofilament. The results of radioautographic studies with radioiodinated CNTF indicate the presence of high‐affinity binding sites on P19 cells. Equilibration of P19 cells with 125ICNTF followed by incubation with cross‐linking reagents reveals evidence for at least two putative receptors of ∼78 and
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