CA2-INDUCED CA2+ RELEASE IN INSECT NEUROSECRETORY NEURONS( RESTING CURRENT AND CA2+)

THE effect of a Ca2+ resting current on spiking and intracellular Ca2 concentration [Ca2+](i) of isolated cockroach dorsal unpaired median neurons was investigated by combining microfluometry (Fura2) with patc h-clamping. The resting current was reduced by 10 mu M 5-nitro-2-(3-ph enylpropylamino)benzoic acid (NPPB) and 10 mu M mefenamic acid, which caused slower spiking of cells. Up-modulation of the resting current b y neurohormone D (NHD, 100 fM to 10 pM) transiently increased [Ca2+](i ). This Ca2+ transient was largely reduced by the ryanodine receptor a ntagonist dantrolene (10 mu M) but it was not reduced by the IP3-recep tor antagonist heparin which indicates Ca2+-induced Ca2+ release. The NHD-effect on [Ca2+](i) was strongly attenuated by NPPB and mefenamic acid. Thus, NHD caused Ca2+-induced Ca2+ release by enhancing the Ca2 resting current. (C) 1998 Lippincott Williams & Wilkins.