ASCARIS-SUUM - CHARACTERIZATION OF TRANSMURAL AND HYPODERMAL POTENTIALS

Electrophysiological measurements demonstrate that an electrochemical potential exists across the body wall of parasitic nematodes. The ioni c dependence of this transmural electrical potential (E(tm)) in the ga strointestinal nematode Ascaris suum was investigated using convention al electrophysiological techniques. E(tm) recorded from intact A. suum maintained in artificial pseudocoelomic fluid (APF) was -40 +/- 12 mV . This potential was more sensitive to external acetate than to Na+, K +, or Cl-, although elimination of most Na+ from the medium significan tly hyperpolarized the body wall. An Ussing chamber and isolated segme nts of A. suum body wall were used to delineate the barrier characteri stics of the individual components of the body wall: the cuticle and t he inward- and outward-facing membranes of the hypodermis. The cuticle (i.e., muscle and hypodermis scraped away) is highly permeable to bot h inorganic and organic ions, with the rank-order of permeability amon g ions tested being K+ > Na+ = Cl- > acetate(-) > gluconate(-). The in ward- and outward-facing membranes of the hypodermis were more polariz ed than the body wall complex, exhibiting potentials in APF of -47.6 /- 6 mV (E(i)) and -74.9 +/- 7 mV (E(o)) versus -26 +/- 8 mV (E(tm) fo r isolated body wall segments), respectively. The electrical potential across the hypodermal membranes became depolarized when high K+ mediu m or low acetate medium was added to the muscle side, but not when add ed to the cuticle side of isolated body wall segments. E(tm), E(o), an d E(i) were unaffected by reduction of Na+, K+, or Cl- concentrations in the recording medium. All three potentials, however, became markedl y depolarized when the temperature of the incubation medium was reduce d. These results indicate that the cuticle/hypodermis complex of A. su um is differentially permeable to both inorganic and organic ions and suggest that active transport of ions or outward diffusion of metaboli c end-products contributes extensively to the maintenance of transmura l electrochemical gradients. (C) 1995 Academic Press, Inc.