Modulation of Na⁺ transport across leech skin by pesticides and heavy metals

Abstract

The aim of the present study was to investigate the effects of environmental pollutants, such as heavy metals and pesticides on ion transport across the skin of the leech (Hirudo medicinalis). We wanted to examine the suitability of this epithelium as a model system for studies concerning the mechanisms of toxic action caused by environmental pollutants. For this purpose we performed Ussing chamber experiments to test three representative heavy metals and pesticides, respectively, for their effects on current flow across leech dorsal integument. Two representatives of each substance class showed distinct effects on ion transport across this epithelium. The heavy metal ions Pb²⁺ and Hg²⁺ produced a significant inhibition of amiloride-sensitive Na⁺ transport across leech skin in concentrations below or close to their limiting values in waste water. Therefore, it seems feasible to use leech skin for future investigations of the toxic actions of these heavy metals. The fact that Pb²⁺ and Hg²⁺ exerted their effects only when applied apically points to a specific action of these divalent cations on ion channels in the apical membrane. However, this inhibition does not seem to be a general feature of divalent cations because Cd²⁺ did not influence ion transport across leech skin at all. Since current flow through amiloride-sensitive Na⁺ channels in typical vertebrate tight epithelia is stimulated by numerous divalent cations, the pronounced inhibition of amiloride-sensitive Na⁺ channels in leech skin by Pb²⁺ and Hg²⁺ might lead to a further differentiation of amiloride-sensitive Na⁺ channels. The two widespread pesticides lindane and promecarb exerted their effects only at comparativ high concentrations. This low sensitivity restricts the usefulness of leech skin as a subject for further analysis of toxicity mechanisms, at least for these two pesticides.