Abstract
Celangulin V (CV) is the main insecticidal constituent of Celastrus angulatus. The V-ATPase H subunit of the midgut cells of lepidopteran larvae is the putative target protein of CV. Here, we compared the effects of CV on the midgut membrane potentials of Mythimna separata and Agrotis ipsilon larvae with those of the Cry1Ab toxin from Bacillus thuringiensis and with those of inactive CV-MIA, a synthetic derivative of CV. We investigated the changes in the apical membrane potentials (V(am)) and basolateral membrane potentials (V(bm)) of the midguts of sixth-instar larvae force-fed with the test toxins. We also measured the V(am) and V(bm) of larval midguts that were directly incubated with the test toxins. Similar to the effect of Cry1Ab, the V(am) of CV-treated midguts rapidly decayed over time in a dose-dependent manner. By contrast, CV-MIA did not influence V(am). Meanwhile, the V(am) of A. ipsilon larval midguts directly incubated with CV decayed less than that of M. separata larval midguts, whereas that of larvae force-fed with CV did not significantly change. Similar to Cry1Ab, CV did not affect the V(bm) of isolated midguts. CV significantly inhibited V-ATPase activity in a dose-dependent manner. Therefore, CV initially inhibits V-ATPase in the apical membrane and affects intracellular pH, homeostasis, and nutrient transport mechanisms in lepidopteran midgut cells.