Age-dependent differences in 125I-nerve growth factor binding properties of rat adrenal chromaffin cells

Nerve growth factor (NGF) has been shown to influence survival, morphology, and transmitter phenotype of young postnatal rat chromaffin cells in vitro. Significant differences in NGF responses of chromaffin cells from newborn rats compared to 8-10-day-old ones have been reported. For this reason we studied equilibrium binding and dissociation kinetics of 125I-NGF on newborn (D1) and 10-day-old (D10) rats. Under equilibrium conditions no differences were found between the two cell types, with respect to dissociation constant (approximately 2.5 X 10(-9) M) and receptor number (10-22,000 per cell). In dissociation experiments D10 chromaffin cells exhibited two classes of NGF receptors, similar to those found in other NGF-responsive cells. From fast receptors 125I-NGF was released rapidly both at 4 degrees C and at 37 degrees C, whereas dissociation from "slow" receptors was observed only at 37 degrees C. The slow receptor class was not found on D1 cells. Instead, more than 50% of specifically bound 125I-NGF did not dissociate in the presence of excess unlabeled NGF at 37 degrees C. These age-dependent differences seem to indicate regulatory developmental changes in NGF-binding properties of rat chromaffin cells.