The Effects of Some Heavy Metals On the Kinetics of Pharyngeal Pumping in Panagrellus Silusiae

Free-living nematodes are relatively resistant to many toxic substances, especially heavy metals. To test whether a cessation of the feeding system is a primary strategy for protection, the effect of chromium, cadmium and copper on the kinetics of pharyngeal pumping of Panagrellus silusiae was studied. As the duration in heavy metal increases, the proportion of worms that are feeding decreases significantly. In this study, a feeding period is defined as 10 or more contractions of the posterior bulb of the pharynx with no more than five seconds between contractions. A contraction is denoted by the inversion of the cuticular flaps of the posterior bulb. In nonfeeding worms (i.e., foragers) virtually all pharyngeal pumping is curtailed. On the other hand, feeding worms, notwithstanding a 24 h duration in the presence of heavy metal, have (1) the same rate of pumping, (2) the same numbers of feeding periods and (3) the same number of contractions per feeding period as untreated organisms. Thus, treatment with heavy metal suppresses pharyngeal pumping either completely or not at all. However, other protective mechanisms must be utilized by the worms because (1) the blockade of the feeding mechanism is not immediate and neither (2) the muscular activity as defined by movement of the organisms nor (3) the quantitative aspects of pharyngeal pumping are altered in worms that continue to feed in the presence of heavy metal.