Insight into the Mode of Action of Celangulin V on the Transmembrane Potential of Midgut Cells in Lepidopteran Larvae

Abstract

Celangulin V (CV) is the main insecticidal constituent of <i>Celastrus angulatus</i>. 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 <i>Mythimna separata</i> and <i>Agrotis ipsilon</i> larvae with those of the Cry1Ab toxin from <i>Bacillus thuringiensis</i> and with those of inactive CV-MIA, a synthetic derivative of CV. We investigated the changes in the apical membrane potentials (<i>V_am</i>) and basolateral membrane potentials (<i>V_bm</i>) of the midguts of sixth-instar larvae force-fed with the test toxins. We also measured the <i>V_am</i> and <i>V_bm</i> of larval midguts that were directly incubated with the test toxins. Similar to the effect of Cry1Ab, the <i>V_am</i> of CV-treated midguts rapidly decayed over time in a dose-dependent manner. By contrast, CV-MIA did not influence <i>V_am</i>. Meanwhile, the <i>V_am</i> of <i>A. ipsilon</i> larval midguts directly incubated with CV decayed less than that of <i>M. separata</i> larval midguts, whereas that of larvae force-fed with CV did not significantly change. Similar to Cry1Ab, CV did not affect the <i>V_bm</i> 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.