CA2- PROPERTIES AND MODULATION BY NEUROHORMONE-D( CURRENTS IN COCKROACH NEURONS )

IN dorsal unpaired median (DUM) neurones isolated from the terminal ga nglion of the cockroach Periplaneta americana two types of Ca2+ curren ts were found: a transient one activated by lower depolarizations (LVA ) and a sustained one activated by higher voltage jumps (HVA). Both cu rrents were strongly reduced by 100 mu M Cd2+; Ni2+ was less effective . The HVA currents were insensitive to dihydropyridines, but sensitive to phenylalkylamines. The LVA component was sensitive to omega-conoto xin GVIA and SK&F 96365 whereas the HVA component was insensitive to b oth blockers. The octapeptide neurohormone D (NHD), a member of the fa mily of adipokinetic hormones (AKH-peptides), is known to increase the spiking frequence in these DUM cells. We demonstrate that NHD increas es the LVA current component and decreases the HVA current component. These effects of NHD can explain the previously found NHD-induced stim ulation of Ca2+ dependent K+ currents.