Binding of insulin and insulin-like growth factor I in bovine chromaffin cells in primary culture.

1. Insulin and insulin-like growth factor I (IGF-I) receptors were studied in bovine chromaffin cells isolated from the medulla by collagenase digestion and kept in primary culture. 2. Specific 125I-labelled insulin binding increased with time in culture with no significant change in the dissociation constant, Kd approximately 0.3 nM. Insulin was nearly 100-fold more potent than IGF-I in displacing 125I-labelled insulin. 3. Affinity crosslinking and SDS gel electrophoresis revealed increased binding of 125I-labelled insulin and 125I-IGF-I with time in culture, the densities of the labelling indicating relatively a much higher expression of IGF-I than insulin receptors in the cells. The apparent molecular weight of both the hormone binding subunits were 135,000, suggesting that the insulin and IGF-I receptors in the adrenal medulla are of the peripheral types. 4. Both receptors thus appeared to be affected by the collagenase treatment but with a subsequent recovery when cells were kept in culture.