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 neuron-like morphological differentiation in response to nerve growth factor (NGF). 2. Chromaffin cells display a large variability in the morphological changes after exposure to NGF. However, a marked tendency to neuronal phenotypic transformation prevails after two weeks in culture. 3. The voltage 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-inactivation parameters of Na currents were compared between control and NGF-treated cells, no significant differences were observed. 4. Peak Na currents in control cells remained < 1 nA throughout the 17 d of observation, 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 > or = 15 d, but inadequate voltage control and neurite spiking prevented a thorough examination. 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 significant changes were observed in control, untreated cells. 5. The increase in Na channel density induced by NGF in chromaffin cells in compatible with the acquisition of the neuronal phenotype. Interestingly, the increase in Na channel expression occurs in slower time scale than in their neoplastic correlate, the PC12 cells. Na channels newly expressed by chromaffin cells after NGF treatment are functionally indistinguishable from those already present before treatment.