Journal of Neuroscience, Vol 13, 2591-2600, Copyright © 1993 by Society for Neuroscience
Extrinsic factors influence the expression of voltage-gated K currents on neonatal rat sympathetic neurons
S McFarlane and E Cooper
Department of Physiology, McGill University, Montreal, Quebec, Canada.
Voltage-gated potassium (K) currents are important in controlling a
neuron's excitability. We have shown previously (McFarlane and Cooper,
1992) that neonatal superior cervical ganglia (SCG) neurons express three
voltage-gated K currents: a noninactivating delayed-rectifier type current
(IK), a rapidly inactivating A-current (IAf), and a slowly inactivating
A-current (IAs). When grown in culture for 4 weeks without other cell
types, SCG neurons lose their expression of IAf and IAs, suggesting that an
extrinsic factor(s) is involved in controlling the expression of these
currents. In vivo, SCG neurons are surrounded by non-neuronal cells.
Therefore, in this study we investigated whether the ganglionic
non-neuronal cells provide a factor required for A- current expression. We
show that postnatal day 1 (P1) SCG neurons continue to express IAf and IAs
when cocultured with their ganglionic non-neuronal cells. Medium
conditioned by ganglionic non-neuronal cells mimics the non-neuronal cell
influence on IAf and IAs expression, suggesting that the effects of
non-neuronal cells are mediated by way of a secreted factor. Ciliary
neurotrophic factor, a factor present in peripheral non-neuronal cells, had
similar effects to those of ganglionic cell-conditioned medium. Moreover,
we find that the dependence of IAf on a non-neuronal cell factor is
developmentally regulated; P14 neurons grown in culture without other cell
types continue to express IAf. However, IAs on P14 neurons maintains its
dependence on a factor from non-neuronal cells. Finally, in addition to
extrinsic control of voltage-gated K currents, we suggest that SCG neurons
use intrinsic mechanisms to coordinate their expression of IAf, IAs, and IK
such that changes in one K current are compensated for by reciprocal
changes in one or more of the other K currents.