Journal of Neurophysiology, Vol 72, Issue 4 1938-1948, Copyright © 1994 by APS
Properties of the sodium current in rat chromaffin cells exposed to nerve growth factor in vitro
L. Islas-Suarez, M. Gomez-Chavarin, R. Drucker-Colin and A. Hernandez-Cruz
Departamento de Neurociencias, Facultad de Medicina, Universidad Nacional Autonoma de Mexico, Mexico City.
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.
