Modulation of levamisole and nicotine toxicity in soil nematodes Caenorhabditis elegans and Caenorhabditis briggsae by moderate heat stress and ambient pH

Abstract

Abstract The influence of moderate heat stress and changes in ambient pH in the range of 6.0 to 8.0 was investigated on two soil nematodes (Caenorhabditis elegans and Caenorhabditis briggsae). Rise of ambient pH from 6.0 to 8.0 increased the sensitivity of nematodes to agonists of nicotinic cholinoreceptors levamisole (30–120 μM) and nicotine (1–4 mM) by 1.5– 5 folds, but not to acetylcholine esterase inhibitor aldicarb (60–240 μM). An increase in temperature up to 30°C caused a steep rise in sensitivity of C. elegans and C. briggsae to levamisole. The influence of ambient pH on sensitivity of C. elegans and C. briggsae to levamisole at 30°C was similar to that at 22°C. Therefore, mechanisms of sensitization of C. elegans to levamisole toxicity by an increase in pH or by temperature rise are different. The most likely mechanism for the increase in levamisole and nicotine toxicity in C. elegans and C. briggsae by a rise in ambient pH is deprotonation of levamisole and nicotine. This study shows that it is desirable to conduct the evaluation of the biological activity of toxicants in nematodes in the pH range 6.0–8.0, and not at a single pH.