A detailed understanding of AP-evoked calcium entry in the axon initial segment of prefrontal pyramidal cells. Several interesting takeaways:
1) There are far more channel types in these cells than others we've examined in the past. Cartwheel cells have only 2 types of CaVs in their initial segments (T-type and R-type). Pyramidal cells, in contrast, have at least 4: T, R, P/Q, and N. L is the only one that is absent.
2) There appear to be hotspots for T-type mediated entry near intracellular stores. We need to examine these further, but it points to an idea that there is a microstructure to the arrangement of channels in this region, akin to how NaVs and KVs are distributed.