Bovine chromaffin cells have insulin-like growth factor-I (IGF-I) receptors: IGF-I enhances catecholamine secretion

The binding of 125I-insulin-like growth factor-I (125I-IGF-I) to bovine chromaffin cells was measured. Chromaffin cell cultures contained 111,000 +/- 40,000 IGF-I binding sites/cell. These sites bound IGF-I with a KD of 1.1 +/- 0.3 nM and had a much lower affinity for insulin. Cross-linking studies showed that 125I-IGF-I bound to a protein that had an Mr of approximately 125,000, similar to the Mr of the alpha subunit of the IGF-I receptor in other tissues. Cells cultured with IGF-I (10 nM) for 4 days exhibited an almost twofold increase in high K+-evoked catecholamine secretion. Insulin was much less potent than IGF-I in enhancing catecholamine secretion. These data indicate that binding of IGF-I to its receptors on chromaffin cells can modulate the function of these cells.