Résumé
Analysis of neuronal development has emphasized the importance of voltage-activated Ca
2+ currents during the initial period of differentiation. We investigated non-N, non-L Ba
2+ currents through Ca
2+ channels in freshly dissociated large diameter embryonic mouse dorsal root ganglion neurons using the whole-cell patch-clamp technique. Two types of ω-agatoxin IVA-sensitive currents were clearly distinguished at embryonic day 13: a sustained P-type current blocked selectively at 30
nM (IC
50=3
nM) and an inactivating Q-type current blocked in the range 50–500
nM (IC
50=120
nM). The P-type Ca
2+ current disappears at day 15 whereas the Q-type Ca
2+ current increased two- to three-fold during the same embryonic period. In contrast, the contribution of the non-L, non-N, ω-agatoxin IVA-resistant current (R-type) was constant during this developmental span. In conclusion, our results clearly show that P- and Q-type Ca
2+ currents are differentially expressed during ontogenesis in large diameter dorsal root ganglion neurons.
The developmental change, which occurs during the period of target innervation, could be related to specific key events such as natural neuron death and onset of synapse formation.