The action potential of chick dorsal root ganglion neurones maintained in cell culture.

Abstract

The directly evoked action potential of dissociated, embryonic chick dorsal root ganglion (DRG) neurons maintained in cell culture was prolonged compared to spinal cord cell spikes and the re-polarization phase was marked by a plateau. Both Ca2+ and Na+ carried inward current across the active soma membrane. Ca2+ because overshooting spikes persisted in tetrodotoxin (TTX) or Na+-free media; in the presence of TTX (or absence of Na+) spike size varied directly with extracellular Ca2+ and spikes were eliminated by Co2+.cntdot.Na+ because spikes persisted in the presence of Co2+ or Ca2+-free media; in the presence of Co2+ (or absence of Ca2+) spike size varied directly with extracellular Na+ and spikes were blocked by TTX. Ca2+ played less if any role in action potentials conducted along sensory nerve cell processes. Conducted spikes could not be evoked in TTX-containing or Na+-free media. A long-lasting depolarization followed the action potential in some neurons. This depolarization was associated with an increase in membrane conductance and appeared to drive the membrane potential to about -30 mV. It persisted when conducted impulses were blocked so it was probably not a recurrent synaptic potential. Combined Ca2+-Na+ spikes observed in isolated sensory neurons in vitro reflect the action potential of adult sensory cells but the possibility that they represent an early stage in development is also discussed.