Ca2+ currents in cockroach neurones: properties and modulation by neurohormone D.

In dorsal unpaired median (DUM) neurones isolated from the terminal ganglion of the cockroach Periplaneta americana two types of Ca2+ currents were found: a transient one activated by lower depolarizations (LVA) and a sustained one activated by higher voltage jumps (HVA). Both currents were strongly reduced by 100 microM Cd2+; Ni2+ was less effective. The HVA currents were insensitive to dihydropyridines, but sensitive to phenylalkylamines. The LVA component was sensitive to omega-conotoxin GVIA and SK&F96365 whereas the HVA component was insensitive to both blockers. The octapeptide neurohormone D (NHD), a member of the family of adipokinetic hormones (AKH-peptides), is known to increase the spiking frequence in these DUM cells. We demonstrate that NHD increases the LVA current component and decreases the HVA current component. These effects of NHD can explain the previously found NHD-induced stimulation of Ca2+ dependent K+ currents.