CALCIUM-ACTIVATED POTASSIUM CHANNELS IN THE UCR-SE-1A LEPIDOPTERAN CELL-LINE FROM THE BEET ARMYWORM (SPODOPTERA-EXIGUA)

Ion channels in the UCR-SE-1a cell line from the beet armyworm (Spodoptera exigua) were studied using the patch-clamp technique in the cell-attached, the inside-out and the outside-out configurations. Contrarily to SF-9 cells from the fall armyworm (Spodoptera frugiperda) which did not display ion channel activity, UCR-SE-1a cells possess 120-pS (in the cell-attached configuration), voltage-dependent potassium channels that are activated in the inside-out configuration by calcium exposure of the cytoplasmic side of the membrane. In the cell-attached configuration, similar channel activation takes place in the presence of the calcium ionophore A23187. The channels are blocked by tetraethylammonium and cobalt ions but are insensitive to the scorpion venom charybdotoxin. They do not appear to belong to any of the well-characterized calcium-activated potassium channels found in mammalian cells. Identical channel activity was observed when UCR-SE-1a cells were exposed to Bacillus thuringiensis CryIC toxin, suggesting that intracellular calcium rises as a result of toxin interaction with the cells. This effect was directly demonstrated by fluorescence videomicroscopy experiments showing that like SF-9 cells, UCR-SE-1a cells loaded with the calcium probe Fura 2 respond to CryIC toxin exposure by an intracellular calcium surge.