PROPERTIES OF THE SODIUM CURRENT IN RAT CHROMAFFIN CELLS EXPOSED TO NERVE GROWTH-FACTOR IN-VITRO

1. This paper examines the electrophysiological properties of cultured rat adrenal chromaffin cells at different stages of neuronlike morpho logical differentiation in response to nerve growth factor (NGF). 2. C hromaffin cells display a large variability in the morphological chang es after exposure to NGF. However, a marked tendency to neuronal pheno typic transformation prevails after two weeks in culture. 3. The volta ge dependence of the macroscopic Na currents, judged by the current to voltage relationship, did not change significantly as a result of NGF treatment. Moreover, when kinetics, half-activation, and half-inactiv ation parameters of Na currents were compared between control and NGF- treated cells, no significant differences were observed. 4. Peak Na cu rrents in control cells remained <1 nA throughout the 17 d of observat ion, whereas currents >1 nA became more frequent after the first week of NGF exposure. Cells with Na currents >2 nA were found routinely in cultures exposed to NGF for greater than or equal to 15 d, but inadequ ate voltage control and neurite spiking prevented a thorough examinati on. Sodium current density in the population of NGF-treated chromaffin cells increased progressively over time, until an apparent plateau (3 .5-fold increase) was reached by the end of the second week. No signif icant changes were observed in control, untreated cells. 5. The increa se in Na channel density induced by NGF in chromaffin cells is compati ble with the acquisition of the neuronal phenotype. Interestingly, the increase in Na channel expression occurs in a slower time scale than in their neoplastic correlate, the PC12 cells. Na channels newly expre ssed by chromaffin cells after NGF treatment are functionally indistin guishable from those already present before treatment.