Dynamic, temperature-sensitive association of 125-i-nerve growth factor in vitro with ganglionic and non-ganglionic...

125-I-NGF was found to associate with embryonic chick dorsal root ganglia (DRG) through two processes. A time-saturable process included the binding of NGF to surface receptors with an apparent affinity constant in the range of 10(-7)M minus 1 and at a level of 4 f moles/mug tissue protein. The second process was time-linear, temperature-sensitive, and included both bound and non-competable NGF. While metabolic inhibitors had little effect, histone and insulin considerably increased the uptake. A comparison of 125-I-NGF and 125-I-peroxidase uptake suggested that the time-linear uptake of 125-I-NGF must include only bound NGF and incubation medium. Sequestration of the proteins taken up was indicated by the lack of release of radiolabeled material at 4 degrees C, even in the presence of native proteins. All these characteristics are consistent with an interpretation that DRG cells can take up NGF and other proteins by a pinocytotic process. Similar NGF binding and uptake properties were found to occur in cells from a variety of other embryonic chick tissues.